Patterns of asexual reproduction of the soybean aphid, Aphis glycines (Matsumura), with and without the secondary symbionts Wolbachia and Arsenophonus, on susceptible and resistant soybean genotypes

Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1 + 2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W-). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1 + 2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations.

Characterization and genetics of multiple soybean aphid biotype resistance in five soybean plant introductions

KEY MESSAGE

Five soybean plant introductions expressed antibiosis resistance to multiple soybean aphid biotypes. Two introductions had resistance genes located in the Rag1, Rag2, and Rag3 regions; one introduction had resistance genes located in the Rag1, Rag2, and rag4 regions; one introduction had resistance genes located in the Rag1 and Rag2 regions; and one introduction had a resistance gene located in the Rag2 region. Soybean aphid (Aphis glycines Matsumura) is the most important soybean [Glycine max (L.) Merr.] insect pest in the USA. The objectives of this study were to characterize the resistance expressed in five plant introductions (PIs) to four soybean aphid biotypes, determine the mode of resistance inheritance, and identify markers associated with genes controlling resistance in these accessions. Five soybean PIs, from an initial set of 3000 PIs, were tested for resistance against soybean aphid biotypes 1, 2, 3, and 4 in choice and no-choice tests. Of these five PIs, PI 587663, PI 587677, and PI 587685 expressed antibiosis against all four biotypes, while PI 587972 and PI 594592 expressed antibiosis against biotypes 1, 2, and 3. F2 populations derived from PI 587663 and PI 587972 were evaluated for resistance against soybean aphid biotype 1, and populations derived from PIs 587677, 587685, and 594592 were tested against biotype 3. In addition, F2:3 plants were tested against biotypes 2 and 3. Genomic DNA from F2 plants was screened with markers linked to Rag1, Rag2, Rag3, and rag4 soybean aphid-resistance genes. Results showed that PI 587663 and PI 594592 each had three genes with variable gene action located in the Rag1, Rag2, and Rag3 regions. PI 587677 had three genes with variable gene action located in the Rag1, Rag2 and rag4 regions. PI 587685 had one dominant gene located in the Rag1 region and an additive gene in the Rag2 region. PI 587972 had one dominant gene located in the Rag2 region controlling antixenosis- or antibiosis-type resistance to soybean aphid biotypes 1, 2, or 3. PIs 587663, 587677, and 587685 also showed antibiosis-type resistance against biotype 4. Information on multi-biotype aphid resistance and resistance gene markers will be useful for improving soybean aphid resistance in commercial soybean cultivars.

Differential Reactions of Soybean Isolines With Combinations of Aphid Resistance Genes Rag1 , Rag2 , and Rag3 to Four Soybean Aphid Biotypes

With the discovery of the soybean aphid ( Aphis glycines Matsumura) as a devastating insect pest of soybean ( Glycine max (L.) Merr.) in the United States, host resistance was recognized as an important management option. However, the identification of soybean aphid isolates exhibiting strong virulence against aphid resistance genes ( Rag genes) has highlighted the need for pyramiding genes to help ensure the durability of host resistance as a control strategy. In this study, soybean isolines with all possible combinations of the resistance and susceptibility alleles at Rag1 , Rag2 , and Rag3 were evaluated for their effectiveness against the four characterized soybean aphid biotypes. All soybean isolines, including the susceptible check carrying none of the resistance alleles (S1/S2/S3), were infested with each biotype in no-choice greenhouse tests, and the aphid populations developed on each isoline were enumerated 14 d after infestation. All gene combinations, with the exception of Rag3 alone, provided excellent protection against biotype 1. Isolines with Rag2 alone or in combination with Rag1 and Rag3 had greater levels of resistance to biotype 2 than those with either Rag1 alone, Rag3 alone, or the Rag1/3 pyramid. For biotype 3, the Rag1/3 and Rag1/2/3 pyramided lines significantly reduced aphid populations compared with all other gene combinations, while the Rag1/2/3 pyramid provided the greatest protection against biotype 4. Overall, the Rag1/2/3 pyramided line conferred the greatest protection against all four biotypes.

Soybean aphid intrabiotype variability based on colonization of specific soybean genotypes

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the most destructive insect pests on soybeans in the United States. One method for managing this pest is through host plant resistance. Since its arrival in 2000, 4 aphid biotypes have been identified that are able to overcome soybean aphid resistance (Rag) genes. A soybean aphid isolate collected from Moline, Illinois readily colonized soybean plants with the soybean aphid resistance gene Rag2, unlike biotypes 1 and 2, but similar to soybean aphid biotype 3. Two no-choice experiments compared the virulence of the Moline isolate with biotype 3. In both experiments, differences in aphid population counts were not significant (P > 0.05) on soybean genotypes LD08-12957a (Rag2) and LD11-5413a (Rag2), but the aphid counts for the Moline isolate were significantly (P < 0.05) lower than the aphid counts for the biotype 3 isolate on the soybean genotypes Dowling (Rag1), LD05-16611 (Rag1), LD11-4576a (Rag1), and PI 567598B (rag1b and rag3). The Moline isolate was a variant of aphid biotype 3, which is the first report showing that soybean aphid isolates classified as the same biotype, based on virulence against specific Rag genes, can differ in aggressiveness or ability to colonize specific host genotypes.

Comparison of Pathogenic Variation among Phakopsora pachyrhizi Isolates Collected from the United States and International Locations, and Identification of Soybean Genotypes Resistant to the U.S. Isolates

A major constraint in breeding for resistance to soybean rust has been the virulence diversity in Phakopsora pachyrhizi populations. In greenhouse experiments, reactions of 18 soybean genotypes to 24 U.S. isolates from 2007 and 2008 and 4 foreign isolates were compared. Reactions of four differentials (Rpp1 to Rpp4) to these U.S. isolates were also compared with reactions to nine foreign isolates and three U.S. isolates from 2004. Principal component analysis (PCA) of the reaction types grouped the U.S. isolates into a single virulence group, whereas each of the foreign isolates had a unique virulence pattern. In another experiment, reactions of 11 differentials to the 24 U.S. isolates were compared and significant interactions (P < 0.001) were found between the isolates and host genotypes for rust severity and uredinia densities. PCA of these two measures of disease placed the 24 isolates into seven or six aggressiveness groups, respectively. In a third experiment, evaluation of 20 soybean genotypes for resistance to the previously established aggressive groups identified 10 genotypes resistant to isolates representing most of the groups. This study confirmed the pathogenic diversity in P. pachyrhizi populations and identified soybean germplasm with resistance to representative U.S. isolates that can be used in breeding.

Inhibitory effects of stilbenes on the growth of three soybean pathogens in culture

The effects of resveratrol and pterostilbene on in vitro growth of three soybean pathogens were tested to determine whether these stilbenic compounds could potentially be targets to increase innate resistance in transgenic soybean plants. Growth of Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum was measured on solid and in liquid media amended with resveratrol and pterostilbene (concentration in the media of resveratrol at 100 μg/ml and pterostilbene at 25 μg/ml). All three fungi were very sensitive to pterostilbene in potato dextrose agar (PDA), which reduced colony area of each of the three pathogens to less than half of the control 3 days after incubation. The three fungal pathogens were less sensitive to resveratrol compared with pterostilbene; however, area under the curve (AUC) calculated from colony areas measured over 3 days was significantly (P < 0.05) less than the control for S. sclerotiorum and R. solani on PDA with resveratrol or pterostilbene. AUC for M. phaseolina on PDA with pterostilbene was significantly (P < 0.05) lower than the control whereas, on PDA with resveratrol, AUC for M. phaseolina was lower than the control but the difference was nonsignificant (P > 0.05). AUC for all three fungi was significantly lower (P < 0.05) on PDA with pterostilbene than with resveratrol. In potato dextrose broth (PDB) shake cultures, AUC for all three fungi was significantly (P < 0.01) lower in pterostilbene than in the control. AUC for R. solani and S. sclerotiorum was significantly lower (P < 0.01) in resveratrol than the control, whereas AUC for M. phaseolina in resveratrol was lower, but not significantly (P > 0.05) different from the control. AUC in pterostilbene was highly significantly (P < 0.01) lower than in resveratrol for M. phaseolina and significantly (P < 0.05) lower for R. solani but the difference for S. sclerotiorum was nonsignificant (P > 0.05). There was a trend for lower mass accumulation of all three fungi in either pterostilbene or resveratrol compared with the control during the course of the experiment; however, S. sclerotiorum appeared to recover from the effects of pterostilbene between days 2 and 4. Results of biochemical analyses of the PDB over time indicated that the three fungi degraded resveratrol, with nearly 75% reduction in concentration in M. phaseolina, 80% in S. sclerotiorum, and 60% in R. solani PDB cultures by day 4 of fungal growth. M. phaseolina and S. sclerotiorum were able to resume growth after early inhibition by resveratrol after its concentration was reduced in the cultures through degradation, whereas R. solani was less efficient in resveratrol degradation and was not able to overcome its inhibitory effects on growth. The capacity to degrade pterostilbene was lowest in M. phaseolina compared with S. sclerotiorum and R. solani and the recovery of M. phaseolina cultures after initial growth inhibition by pterostilbene was minimal. The potential products of resveratrol and pterostilbene degradation by fungi were identified to be dimers and various oxidation products.

Regulation of plant immunity through modulation of phytoalexin synthesis

Soybean hairy roots transformed with the resveratrol synthase and resveratrol oxymethyl transferase genes driven by constitutive Arabidopsis actin and CsVMV promoters were characterized. Transformed hairy roots accumulated glycoside conjugates of the stilbenic compound resveratrol and the related compound pterostilbene, which are normally not synthesized by soybean plants. Expression of the non-native stilbenic phytoalexin synthesis in soybean hairy roots increased their resistance to the soybean pathogen Rhizoctonia solani. The expression of the AhRS3 gene resulted in 20% to 50% decreased root necrosis compared to that of untransformed hairy roots. The expression of two genes, the AhRS3 and ROMT, required for pterostilbene synthesis in soybean, resulted in significantly lower root necrosis (ranging from 0% to 7%) in transgenic roots than in untransformed hairy roots that had about 84% necrosis. Overexpression of the soybean prenyltransferase (dimethylallyltransferase) G4DT gene in soybean hairy roots increased accumulation of the native phytoalexin glyceollin resulting in decreased root necrosis.

Identification and molecular mapping of two soybean aphid resistance genes in soybean PI 587732

Soybean [Glycine max (L.) Merr.] continues to be plagued by the soybean aphid (Aphis glycines Matsumura: SA) in North America. New soybean resistance sources are needed to combat the four identified SA biotypes. The objectives of this study were to determine the inheritance of SA resistance in PI 587732 and to map resistance gene(s). For this study, 323 F2 and 214 F3 plants developed from crossing PI 587732 to two susceptible genotypes were challenged with three SA biotypes and evaluated with genetic markers. Choice tests showed that resistance to SA Biotype 1 in the first F2 population was controlled by a gene in the Rag1 region on chromosome 7, while resistance to SA Biotype 2 in the second population was controlled by a gene in the Rag2 region on chromosome 13. When 134 F3 plants segregating in both the Rag1 and Rag2 regions were tested with a 1:1 mixture of SA Biotypes 1 and 2, the Rag2 region and an interaction between the Rag1 and Rag2 regions were significantly associated with the resistance. Based on the results of the non-choice tests, the resistance gene in the Rag1 region in PI 587732 may be a different allele or gene from Rag1 from Dowling because the PI 587732 gene showed antibiosis type resistance to SA Biotype 2 while Rag1 from Dowling did not. The two SA resistance loci and genetic marker information from this study will be useful in increasing diversity of SA resistance sources and marker-assisted selection for soybean breeding programs.

Inheritance of soybean aphid resistance in 21 soybean plant introductions

KEY MESSAGE

The Rag2 region was frequently identified among 21 F 2 populations evaluated for soybean aphid resistance, and dominant gene action and single-gene resistance were also commonly identified. The soybean aphid [Aphis glycines Matsumura (Hemiptera: Aphididae)] is one of the most important insect pests of soybean [Glycine max (L.) Merr] in the northern USA and southern Canada, and four resistance loci (Rag1-rag4) have been discovered since the pest was identified in the USA in 2000. The objective of this research was to determine whether resistance expression in recently identified soybean aphid-resistant plant introductions (PIs) was associated with the four Rag loci using a collection of 21 F2 populations. The F2 populations were phenotyped with soybean aphid biotype 1, which is avirulent on plants having any of the currently identified Rag genes, using choice tests in the greenhouse and were tested with genetic markers linked to the four Rag loci. The phenotyping results indicate that soybean aphid resistance is controlled by a single dominant gene in 14 PIs, by two genes in three PIs, and four PIs had no clear Mendelian inheritance patterns. Genetic markers flanking Rag2 were significantly associated with aphid resistance in 20 PIs, the Rag1 region was significantly identified in five PIs, and the Rag3 region was identified in one PI. These results show that single dominant gene action at the Rag2 region may be a major source for aphid resistance in the USDA soybean germplasm collection.

Characterization and quantification of fungal colonization of Phakopsora pachyrhizi in soybean genotypes

Soybean rust, caused by the fungus Phakopsora pachyrhizi, is an economically important disease of soybean with potential to cause severe epidemics resulting in significant yield losses. Host resistance is one of the management tools to control this disease. This study compared soybean genotypes exhibiting immunity, complete and incomplete resistance, and susceptibility to an isolate of P. pachyrhizi based on visual assessment of reaction type, other visual traits such as sporulation, quantitative measurements of the amount of fungal DNA (FDNA) present in leaf tissues, and data on infection and colonization levels. Soybean genotype UG5 (immune), and plant introduction (PI) 567102B and PI 567104B (complete resistance) had lower quantities of uredinia and FDNA than four other genotypes with incomplete resistance. Based on microscopic observations, early events of spore germination, appressorium formation, and fungal penetration of the epidermis occurred within 24 h postinoculation and were similar among the tested soybean genotypes. Differences in infection among the genotypes were evident once the hyphae penetrated into the intercellular spaces between the mesophyll cells. At 2 days after inoculation (dai), soybean genotype Williams 82 had a significantly (P < 0.05) higher percentage of hyphae in the mesophyll tissue than other soybean genotypes, with UG5 having significantly (P < 0.05) lower percentages than all of the other soybean genotypes at 3, 4, and 5 dai. The percentage of interaction sites with mesophyll cell death was significantly (P < 0.05) higher in UG5 than other genotypes at 3, 4, and 5 dai. There was a significant positive correlation (r = 0.30, P < 0.001) between quantities of hyphae in the mesophyll cells and FDNA. These results demonstrated that incompatible soybean-P. pachyrhizi interaction results in restricted hyphal development in mesophyll cell tissue, likely due to hypersensitive apoptosis.

Glyceollin is an important component of soybean plant defense against Phytophthora sojae and Macrophomina phaseolina

The response of soybean transgenic plants, with suppressed synthesis of isoflavones, and nontransgenic plants to two common soybean pathogens, Macrophomina phaseolina and Phytophthora sojae, was studied. Transgenic soybean plants of one line used in this study were previously generated via bombardment of embryogenic cultures with the phenylalanine ammonia lyase, chalcone synthase, and isoflavone synthase (IFS2) genes in sense orientation driven by the cotyledon-preferable lectin promoter (to turn genes on in cotyledons), while plants of another line were newly produced using the IFS2 gene in sense orientation driven by the Cassava vein mosaic virus constitutive promoter (to turn genes on in all plant parts). Nearly complete inhibition of isoflavone synthesis was found in the cotyledons of young seedlings of transgenic plants transformed with the IFS2 transgene driven by the cotyledon-preferable lectin promoter compared with the untransformed control during the 10-day observation period, with the precursors of isoflavone synthesis being accumulated in the cotyledons of transgenic plants. These results indicated that the lectin promoter could be active not only during seed development but also during seed germination. Downregulation of isoflavone synthesis only in the seed or in the whole soybean plant caused a strong inhibition of the pathogen-inducible glyceollin in cotyledons after inoculation with P. sojae, which resulted in increased susceptibility of the cotyledons of both transgenic lines to this pathogen compared with inoculated cotyledons of untransformed plants. When stems were inoculated with M. phaseolina, suppression of glyceollin synthesis was found only in stems of transgenic plants expressing the transgene driven by a constitutive promoter, which developed more severe infection. These results provide further evidence that rapid glyceollin accumulation during infection contributes to the innate soybean defense response.

Effect of Fungicide Application and Cultivar on Soybean Green Stem Disorder

Green stem disorder of soybean (Glycine max) has increasingly become a nuisance for soybean producers. The disorder is distinguished from other manifestations of delayed plant maturity by the delayed senescence of stems only, with normal pod ripening and seed maturation. The primary objective of the first study was to determine whether green stem disorder increased with a fungicide treatment. Field cages to isolate soybean plants to prevent insect interactions were used and treatments included maturity group (MG) II insensitive and sensitive soybean cultivars with or without fungicide applications. A secondary objective was to determine fungi potentially associated with the disorder. The results indicated significant elevation of the incidence of green stem disorder when using a fungicide. Species of Diaporthe or Phomopsis and Macrophomina phaseolina were more frequent in stems without the disorder, whereas species of Colletotrichum were found mostly in stems with the disorder. In another study, field experiments were conducted without cages in replicated field plots to compare the effects of fungicides with different chemistries and timing of fungicide application on incidence of green stem disorder using green stem disorder MG II- and MG III-sensitive and insensitive soybean cultivars. There was a significant increase in percentage of green stem disorder due to fungicide application, depending on fungicide chemistry, timing of application, year, location, and cultivar sensitivity to green stem disorder. Generally, Headline and Headline-Domark applications resulted in higher incidence of green stem disorder than Domark alone or the nonsprayed control, with over 50% incidence in many cases. Higher percent green stem disorder was significantly (P < 0.05) associated with higher yields in 11 of the 28 trials. From the results of this research, soybean producers should be aware of the possible risk that fungicide application may have in increasing incidence of green stem disorder. In addition, producers can help manage green stem disorder by selecting soybean cultivars reported to be consistently insensitive to the disorder.

A Cut-Stem Inoculation Technique to Evaluate Soybean for Resistance to Macrophomina phaseolina

Charcoal rot of soybean is caused by the fungal pathogen Macrophomina phaseolina. Effective and reliable techniques to evaluate soybean for resistance to this fungus are needed to work toward a management scheme that would utilize host resistance. Three experiments were conducted to investigate the use of a cut-stem inoculation technique to evaluate soybean genotypes for resistance to M. phaseolina. The first experiment compared aggressiveness of M. phaseolina isolates collected from soybean on different soybean genotypes. Significant (P < 0.05) differences among the isolates and genotypes for relative area under disease progress curve (RAUDPC) were found without a significant isolate-genotype interaction. The second experiment compared 14 soybean genotypes inoculated with M. phaseolina in multiple trials conducted in two environments, the greenhouse and growth chamber. Significant (P < 0.05) differences among environments and highly significant (P < 0.001) differences among soybean genotypes for RAUDPC were found. The environment-genotype interaction was nonsignificant (P > 0.05). Soybean genotypes DT97-4290, DT98-7553, DT98-17554, and DT99-16864 had significantly (P < 0.05) lower RAUDPC than 7 of the 14 genotypes. The third experiment evaluated resistance in selected Phaseolus spp. and soybean genotypes. The range of RAUDPC for Phaseolus spp. was similar to that of soybean. The Phaseolus lunatus 'Bush Baby Lima' had significantly (P < 0.05) lower RAUDPC than P. vulgaris genotypes evaluated. The cut-stem inoculation technique, which has several advantages over field tests, successfully distinguished differences in aggressiveness among M. phaseolina isolates and relative differences among soybean genotypes for resistance to M. phaseolina comparable with results of field tests.

Identification of quantitative trait loci controlling gene expression during the innate immunity response of soybean

Microbe-associated molecular pattern-triggered immunity (MTI) is an important component of the plant innate immunity response to invading pathogens. However, most of our knowledge of MTI comes from studies of model systems with relatively little work done with crop plants. In this work, we report on variation in both the microbe-associated molecular pattern-triggered oxidative burst and gene expression across four soybean (Glycine max) genotypes. Variation in MTI correlated with the level of pathogen resistance for each genotype. A quantitative trait locus analysis on these traits identified four loci that appeared to regulate gene expression during MTI in soybean. Likewise, we observed that both MTI variation and pathogen resistance were quantitatively inherited. The approach utilized in this study may have utility for identifying key resistance loci useful for developing improved soybean cultivars.

Comparisons of Visual Rust Assessments and DNA Levels of Phakopsora pachyrhizi in Soybean Genotypes Varying in Rust Resistance

Soybean resistance to Phakopsora pachyrhizi, the cause of soybean rust, has been characterized by the following three infection types: (i) immune response (IM; complete resistance) with no visible lesions, (ii) resistant reaction with reddish brown (RB) lesions (incomplete resistance), and (iii) susceptible reaction with tan-colored (TAN) lesions. Based on visual assessments of these phenotypes, single gene resistance in soybean to P. pachyrhizi has been documented, but colonization within infected tissues based on fungal DNA (FDNA) levels in different soybean genotypes had not been analyzed. The research used a quantitative polymerase chain reaction (Q-PCR) assay to compare visual disease assessment to FDNA in controlled inoculation experiments using two isolates of P. pachyrhizi. The objective of the first experiment was to compare data from digital visual disease assessment to FDNA from Q-PCR assays using digital visual disease assessment using five resistant soybean genotypes (one IM and four RB) and five susceptible genotypes (TAN). The objective of the second experiment was to quantify FDNA using Q-PCR at different time points after inoculation to determine if levels of fungal colonization differed in five soybean genotypes with different levels of resistance (one IM, two RB, and two TAN). For experiment 1, the numbers of uredinia and uredinia per lesion on four of the five resistant soybean genotypes were lower (P < 0.05) than the other six genotypes. Significant differences (P < 0.05) in FDNA concentrations were found among soybean genotypes with TAN lesions and among soybean genotypes with RB lesions. Soybean cultivar UG5 (IM phenotype) had significantly less (P < 0.05) FDNA than all of the other genotypes. Some genotypes that produced TAN lesions had significantly lower (P < 0.05) or non-significantly different FDNA concentrations compared to those genotypes that produced RB lesions. For experiment 2, the regression of FDNA on days after inoculation was significant (P < 0.01) with positive slopes for all genotypes except for UG5, in which FDNA declined over time, indicating a reduction of fungal colonization. The results of this Q-PCR FDNA screening technique demonstrates its use to distinguish different types of resistance, and could be used to facilitate the evaluation of soybean breeding populations, where precise quantification of incomplete and/or partial resistance is needed to identify and map quantitative trait loci.

Carbon utilization profiles of Fusarium virguliforme isolates

Fusarium virguliforme is the cause of sudden death syndrome in soybean. Physiological variability among isolates of the fungus is unknown. One way to measure physiologic variability is to analyze growth on different carbon sources. The carbon source utilization profiles of 18 F. virguliforme isolates were examined using the Biolog FF 96-well microplate, which contains 95 different carbon sources. The utilization of dextrin,D-mannitol, maltotriose,D-lactic acid methyl ester, N-acetyl-D-galactosamine, salicin, D-trehalose, and L-alanine differed significantly among isolates (P = 0.05). Carbon sources were grouped into 3 clusters based on their ability to promote growth of F. virguliforme, after calculating Euclidean distances among them. About 12% of the carbon sources promoted a high amount of mycelial growth, 39% promoted a medium amount of growth, and 49% promoted a low amount of mycelial growth; the latter was not significantly different from the water blank control. A hierarchical tree diagram was produced for the 18 isolates based on their carbon source utilization profiles using Ward's hierarchical analysis method. Two main clusters of isolates were formed. One cluster represented greater average mycelial growth on all of the carbon sources than the other cluster. In this study, variability in carbon source utilization among F. virguliforme isolates was evident, but the results were not associated with geographic origin of the isolates, year collected, or published data on aggressiveness. Additional research is needed to determine if these carbon utilization profiles are associated with other biological characteristics, like spore germination, propagule formation, and saprophytic competitiveness.

Production of Macrophomina phaseolina Conidia by Multiple Soybean Isolates in Culture

Macrophomina phaseolina is the cause of charcoal rot of soybean (Glycine max). Resistance to M. phaseolina in commercial soybean cultivars is not common but is needed in locations where the disease is chronic and severe. The objective of this study was to develop a reliable method to produce sufficient M. phaseolina conidia that can be used to inoculate soybean plants in a high-throughput resistance-screening program. Production of pycnidia is not common on most culture media, such as potato dextrose agar, but can be produced on media containing plant parts or oilseed extracts. Seven semi-defined media were tested to induce pycnidia production. Results indicated that the number of pycnidia that were produced by eight M. phaseolina isolates was dependent on induction medium; however, peanut butter extract-saturated filter paper placed over soynut butter extract agar (PESEA) allowed for greater pycnidia and conidia production than the other media tested. Production of pycnidia on PESEA ranged from 269 to 1,082 per plate. There were no differences among isolates in germination of conidia produced on PESEA, which averaged 83 ± 2% germination. A conidial suspension from one M. phaseolina isolate produced on PESEA and inoculated onto soybean radicles significantly distinguished (P < 0.01) 'DT97-4290', a soybean genotype with partial resistance to charcoal rot, from a susceptible genotype, 'LS98-0358'. Results of this study indicated that multiple isolates of M. phaseolina from soybean produced sufficient amounts of conidia on PESEA to use as inoculum. This conidia inoculum production method will facilitate soybean charcoal rot resistance screening evaluation with different soybean isolates.

Response of soybean pathogens to glyceollin

Plants recognize invading pathogens and respond biochemically to prevent invasion or inhibit colonization in plant cells. Enhancing this response in crop plants could improve sustainable methods to manage plant diseases. To enhance disease resistance in soybean, the soybean phytoalexin glyceollin was assessed in soybean hairy roots of two soybean genotypes, Spencer and PI 567374, transformed with either soybean isoflavone synthase (IFS2) or chalcone synthase (CHS6) genes that were inoculated with the soybean pathogens Diaporthe phaseolorum var. meridionales, Macrophomina phaseolina, Sclerotinia sclerotiorum, and Phytophthora sojae. The hairy-root-transformed lines had several-fold decreased levels of isoflavone daidzein, the precursor of glyceollin, and considerably lower concentrations of glyceollin induced by pathogens measured 5 days after fungal inoculation compared with the nontransformed controls without phenolic transgenes. M. phaseolina, P. sojae, and S. sclerotiorum grew much more on IFS2- and CHS6-transformed roots than on control roots, although there was no significant difference in growth of D. phaseolorum var. meridionales on the transformed hairy-root lines. In addition, glyceollin concentration was lower in D. phaseolorum var. meridionales-inoculated transformed and control roots than roots inoculated with the other pathogens. Glyceollin inhibited the growth of D. phaseolorum var. meridionales, M. phaseolina, P. sojae, S. sclerotiorum, and three additional soybean pathogens: Cercospora sojina, Phialophora gregata, and Rhizoctonia solani. The most common product of glyceollin conversion or degradation by the pathogens, with the exception of P. sojae, which had no glyceollin degradation products found in the culture medium, was 7-hydroxyglyceollin.

Fine mapping of the soybean aphid-resistance gene Rag2 in soybean PI 200538

The discovery of biotype diversity of soybean aphid (SA: Aphis glycines Matsumura) in North America emphasizes the necessity to identify new aphid-resistance genes. The soybean [Glycine max (L.) Merr.] plant introduction (PI) 200538 is a promising source of SA resistance because it shows a high level of resistance to a SA biotype that can overcome the SA-resistance gene Rag1 from 'Dowling'. The SA-resistance gene Rag2 was previously mapped from PI 200538 to a 10-cM marker interval on soybean chromosome 13 [formerly linkage group (LG) F]. The objective of this study was to fine map Rag2. This fine mapping was carried out using lines derived from 5,783 F(2) plants at different levels of backcrossing that were screened with flanking genetic markers for the presence of recombination in the Rag2 interval. Fifteen single nucleotide polymorphism (SNP) markers and two dominant polymerase chain reaction-based markers near Rag2 were developed by re-sequencing target intervals and sequence-tagged sites. These efforts resulted in the mapping of Rag2 to a 54-kb interval on the Williams 82 8x assembly (Glyma1). This Williams 82 interval contains seven predicted genes, which includes one nucleotide-binding site-leucine-rich repeat gene. SNP marker and candidate gene information identified in this study will be an important resource in marker-assisted selection for aphid resistance and for cloning the gene.

Rapid-cycling populations of brassica

Rapid-cycling populations of six economically important species in the genus Brassica have unusual potential for resolving many problems in plant biology and for use in education. Rapid-cycling brassicas can produce up to ten generations of seed per year and serve as models for research in genetics, host-parasite relations, molecular biology, cell biology, plant biochemistry, population biology, and plant breeding. Brassicas are a highly diverse group of crop plants that have great economic value as vegetables and as sources of condiment mustard, edible and industrial oil, animal fodder, and green manure. These plants can also be used in the classroom as convenient, rapidly responding, living plant materials for "hands on" learning at all levels of our educational system.

A new soybean aphid (Hemiptera: Aphididae) biotype identified

Shortly after its arrival, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), became established as the most important insect pest of soybean, Glycine max L. (Merr.), in the northern part of the North American soybean production region. Soybean resistance is an environmentally sustainable method to manage the pest and new soybean aphid resistant cultivars are beginning to be deployed into production. However, an earlier study identifying a soybean aphid biotype that could colonize plants with the Rag1 resistance gene has raised concerns about the durability of soybean aphid resistance genes. Choice and nonchoice tests conducted in this study characterized the colonization of a soybean aphid isolate, collected from the overwintering host Frangula alnus P. Mill in Springfield Fen, IN, on different aphid resistant soybean genotypes. This isolate readily colonized plants with the Rag2 resistance gene, distinguishing it from the two biotypes previously characterized and indicating that it represented a new biotype named biotype 3. The identification of soybean aphid biotypes that can overcome Rag1 and Rag2 resistance, even before soybean cultivars with the resistance genes have been deployed in production, suggests that there is high variability in virulence within soybean aphid populations present in North America. Such variability in virulence gives the pest a high potential to adapt to and reduce the effective life of resistance genes deployed in production. The search for new soybean aphid resistance genes must, therefore, continue, along with the development of alternative sustainable strategies to manage the pest.

Fine mapping the soybean aphid resistance gene Rag1 in soybean

The soybean aphid (Aphis glycines Matsumura) is an important soybean [Glycine max (L.) Merr.] pest in North America. The dominant aphid resistance gene Rag1 was previously mapped from the cultivar 'Dowling' to a 12 cM marker interval on soybean chromosome 7 (formerly linkage group M). The development of additional genetic markers mapping closer to Rag1 was needed to accurately position the gene to improve the effectiveness of marker-assisted selection (MAS) and to eventually clone it. The objectives of this study were to identify single nucleotide polymorphisms (SNPs) near Rag1 and to position these SNPs relative to Rag1. To generate a fine map of the Rag1 interval, 824 BC(4)F(2) and 1,000 BC(4)F(3) plants segregating for the gene were screened with markers flanking Rag1. Plants with recombination events close to the gene were tested with SNPs identified in previous studies along with new SNPs identified from the preliminary Williams 82 draft soybean genome shotgun sequence using direct re-sequencing and gene-scanning melt-curve analysis. Progeny of these recombinant plants were evaluated for aphid resistance. These efforts resulted in the mapping of Rag1 between the two SNP markers 46169.7 and 21A, which corresponds to a physical distance on the Williams 82 8x draft assembly (Glyma1.01) of 115 kilobase pair (kb). Several candidate genes for Rag1 are present within the 115-kb interval. The markers identified in this study that are closely linked to Rag1 will be a useful resource in MAS for this important aphid resistance gene.

Differential Responses of Resistant Soybean Entries to Isolates of Phakopsora pachyrhizi

Soybean rust, caused by the fungus Phakopsora pachyrhizi, was detected in the continental United States in 2004. Several new sources of resistance to P. pachyrhizi have been identified in soybean (Glycine max); however, there is limited information about their resistance when challenged with additional U.S. and international isolates. Resistance of 20 soybean (G. max) entries was compared after inoculation with 10 P. pachyrhizi isolates, representing different geographic and temporal origins. Soybean entries included 2 universal susceptible cultivars, 4 sources of soybean rust resistance genes (Rpp_1-4), and 4 and 10 resistant entries selected from field trials in Paraguay and Vietnam, respectively. Of the known Rpp_1-4 sources of resistance, plant introduction (PI) 459025B (Rpp₄) produced reddish-brown (RB) lesions in response to all of the P. pachyrhizi isolates, while PI 230970 (Rpp₂) produced RB lesions to all isolates except one from Taiwan, in response to which it produced a susceptible tan (TAN) lesion. PI 200492 (Rpp₁) and PI 462312 (Rpp₃) produced TAN lesions in response to most P. pachyrhizi isolates. The resistant entries selected from Paraguay and Vietnam varied considerably in their responses to the 10 P. pachyrhizi isolates, with M 103 the most susceptible and GC 84058-18-4 the most resistant. The reaction patterns on these resistant entries to the P. pachyrhizi isolates were different compared with the four soybean accessions with the Rpp genes, indicating that they contain novel sources of rust resistance. Among the P. pachyrhizi isolates, TW 72-1 from Taiwan and IN 73-1 from India produced the most susceptible and resistant reactions, respectively, on the soybean entries.

Green Stem Disorder of Soybean

Green stem disorder of soybean (Glycine max) is characterized by delayed senescence of stems with normal pod ripening and seed maturation. Three different field research approaches were designed to determine the relationship of green stem disorder to Bean pod mottle virus (BPMV) and other potential factors that may be involved in causing this disorder. The first research approach surveyed green stem disorder and BPMV in individual plants monitored in several commercial soybean fields during three growing seasons. Leaf samples from maturing plants (growth stage R6) were tested by enzyme-linked immunosorbent assay (ELISA) for BPMV. The percentage of monitored plants infected with BPMV at growth stage R6 in some fields was higher than the incidence of green stem disorder at harvest maturity. Many plants infected with BPMV did not develop green stem disorder, and conversely, many plants that had green stem disorder were not infected with BPMV. According to a chi-square test of independence, the data indicated that green stem disorder was independent of BPMV infection at growth stage R6 (P = 0.98). A second research approach compared green stem disorder incidence in an identical set of soybean entries planted in two locations with different levels of natural virus infection. Despite differences in virus infection, including BPMV incidence, 20 of 24 entries had similar green stem disorder incidence at the two locations. A third research approach completed over two growing seasons in field cages showed that green stem disorder developed without BPMV infection. BPMV infection did not increase green stem disorder incidence in comparison to controls. Bean leaf beetle, leaf hopper, or stinkbug feeding did not have an effect on the incidence of green stem disorder. The cause of the green stem disorder remains unknown.

Resistance of Glycine species and various cultivated legumes to the soybean aphid (Homoptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura, is a new pest of soybean, Glycine max (L.) Merr., in North America. It has become widespread on soybean in North America since it was first identified in the Midwest in 2000. Species of Rhamnus L. (buckthorn) are the primary hosts of A. glycines, and soybean is known as a secondary host. There is limited information about the secondary host range of A. glycines. Aphid colonization on various legume hosts was compared in choice experiments. Aphid colonization occurred on species in the genus Glycine Wild. No colonization occurred on Lablab purpureus (L.) Sweet, Lens culinaris Medik, Phaseolus vulgaris L., Pisum sativum L., or species of Vicia L. and Vigna Savi. Colonization was limited or aphids were transient on species of Medicago L., Phaseolus L., and Trifolium L. There were significant differences in aphid colonization among Medicago truncatula accessions with numbers ranging from 7 to 97 aphids per plant. Six Glycine soja Sieb. & Zucc. accessions were as resistant as G. max accessions to A. glycines; these may represent novel sources of A. glycines resistance not found in G. max. Antibiosis was found to play a large role in the expression of resistance in three of the G. soja accessions. Results of this study indicated that G. max and G. soja were the best secondary hosts of A. glycines; however, its secondary host range may include other leguminous species. Therefore, A. glycines did not seem to have a highly restricted monophagous secondary host range.

Effect of three resistant soybean genotypes on the fecundity, mortality, and maturation of soybean aphid (Homoptera: Aphididae)

The fecundity, longevity, mortality, and maturation of the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), were characterized using three resistant soybean, Glycine max (L.) Merrill, genotypes ('Dowling', 'Jackson', and PI200538 'Sugao Zarai') and two susceptible genotypes ('Pana' and 'Loda'). Antibiosis in the resistant genotypes was demonstrated by a significant decrease in fecundity and longevity and increased mortality of A. glycines. Aphid fecundity, measured as number of offspring produced in the first 10 d by each viviparous aptera, was higher on Pana than on the resistant genotypes. Aphid longevity, the mean number of days a 1-d-old adult lived, was 7 d longer on Pana than on Dowling and Jackson. The mortality of both viviparous apterae and nymphs on resistant genotypes was significantly higher than on susceptible genotypes. A greater number of first instars survived to maturation stage (date of first reproduction) on susceptible plants than on resistant plants. None of the first instars placed on Dowling and PI200538 leaves survived to maturation. Observations of aphid behavior on leaves indicated that aphids departed from the leaves of resistant plants 8-24 h after being placed on them, whereas they remained indefinitely on leaves of susceptible cultivars and developed colonies. Reduced feeding due to ingestion of potentially toxic compounds in soybean may explain the possible mechanism of resistance to the soybean aphid.

Occurrence of Seed Coat Mottling in Soybean Plants Inoculated with Bean pod mottle virus and Soybean mosaic virus

Soybean seed coat mottling often has been a problematic symptom for soybean growers and the soybean industry. The percentages of seed in eight soybean lines with seed coat mottling were evaluated at harvest after inoculating plants during the growing season with Bean pod mottle virus (BPMV), Soybean mosaic virus (SMV), and both viruses inside an insect-proof cage in the field. Results from experiments conducted over 2 years indicated that plants infected with BPMV and SMV, alone or in combination, produced seed coat mottling, whereas noninoculated plants produced little or no mottled seed. BPMV and SMV inoculated on the same plants did not always result in higher percentages of mottled seed compared with BPMV or SMV alone. There was significant virus, line, and virus-line interaction for seed coat mottling. The non-seed-coat-mottling gene (Im) in Williams isoline L77-5632 provided limited, if any, protection against mottling caused by SMV and none against BPMV. The Peanut mottle virus resistance gene Rpv1 in Williams isoline L85-2308 did not give any protection against mottling caused by SMV, whereas the SMV resistance gene Rsv1 in Williams isoline L78-379 and the resistance gene or genes in the small-seeded line L97-946 gave high levels of protection against mottling caused by SMV. The correlations (r = 0.77 for year 2000 and r = 0.89 for year 2001) between virus infection of the parent plant and seed coat mottling were significant (P = 0.01), indicating that virus infection of plants caused seed coat mottling.

Wireless replacement of the "lost" central venous line in children

Although the achievement of central venous access in children is often difficult maintenance of access is often frustrated by the tendency of the small-caliber central venous line (CVL) to thrombose despite adequate heparinization or-worse yet-be inadvertently removed. Traditional replacement over wire (Seldinger technique) is often not an option for these "lost" CVLs. Over the past 7 years we have used a wireless technique of CVL replacement to re-establish central access in children. The charts of 125 children who underwent wireless CVL replacement at various institutions between January 1995 and July 2000 were retrospectively reviewed. The wireless technique involves replacement of CVL by direct insertion through the previous catheter tract marked by the old puncture site. Plain film was used to confirm the line position postprocedure. The technique was applied predominantly to percutaneously placed 3- to 4-F CVLs with distal port thrombosis or those that had been inadvertently removed. Successful replacement was defined as re-establishment of previous line position and the ability to flush/draw blood through all ports. Wireless replacement was successful in 120 of 125 cases (96.0%). Recannulization was successful in CVLs as new as 3 days old and those removed for as long as 24 hours. Of the five unsuccessful cases, however, two CVLs were >3 weeks old, but >6 hours had elapsed since removal. The remaining three cases were CVLs that were <3 days old. There were no intra- or postoperative complications, notably air embolism. We conclude that wireless CVL replacement in children can be performed safely and successfully in children who have lost central access not amenable to replacement via the traditional Seldinger technique. The often difficult chore of re-establishing central access at a new site in small children can thus be avoided.

Laparoscopic splenectomy in children with hematological disorders: preliminary experience at the Children's Hospital of New Orleans

Minimally invasive surgery has recently gained acceptance as the surgical approach of choice for a variety of surgical disorders in children. Although traditional open surgery is still regarded as the standard approach for a splenectomy in children when necessary for hematologic disorders a few cases of successful laparoscopic splenectomy (LS) have been reported. We present our initial 11 cases of LS in children assessing surgical outcome. Eleven patients ages 2 through 15 years underwent LS between June of 1996 and July of 1999 at the Children's Hospital of New Orleans. Indications for surgery included idiopathic thrombocytopenic purpura, congenital spherocytosis, and hemolytic anemia. In all patients the diameter of the spleen was less than 15 cm. Surgical outcome was assessed according to the following parameters: operative time, postoperative length of stay, postoperative morbidity, and cosmetic results. Data were accumulated on the basis of retrospective chart review. LS was completed in all 11 patients. Postoperative morbidity was minimal and the median postoperative stay was 2.4 days (range 1-5). Mean operative time was 3 hours and 10 minutes (range 1.5-7 hours) with the last six procedures completed in an average of just over 2 hours. Intravenous analgesia was discontinued in <48 hours in all patients. Cosmetic results were judged excellent in all cases. We conclude that LS was safe in children with certain hematologic disorders. Adequate selection of patients, appropriate preoperative preparation of patients, meticulous surgical technique, and careful postoperative care were key factors in obtaining the same long-term results as with open surgery.

Video-assisted thoracoscopic surgery for children with stage II empyema

Children with stage II empyema often fail traditional medical management, frequently succumbing to the effective albeit morbid clutches of thoracotomy. Video-assisted thoracoscopic surgery (VATS) has been recently introduced as a viable and potentially less morbid alternative to open thoracotomy. We review our VATS experience in children with empyema, assessing surgical outcome. Between August 1996 and March 1999, 13 patients at our institution with stage II empyema that did not respond to conventional medical management underwent a modified VATS with decortication. Data from retrospective chart review reflects intraoperative findings and postoperative course, including average time to defervescence, removal of thoracostomy tube, and hospital discharge. VATS was completed in all 13 patients. All intraoperative cultures of pleural fluid and fibrinopurulent debris obtained at VATS showed no growth. The average time to defervescence was 2.2 days (range, 0-4 days) and to removal of thoracostomy tube 3.6 days (range, 2-5 days). Average total chest tube days in patients with pre-VATS thoracostomy (n = 6) was 14.5 days (range, 8-37 days) versus 3.1 days (range, 2-5 days) in patients (n = 7) who underwent primary VATS (t test, p < 0.05). The average time to surgical discharge after VATS was 5.8 days (range, 3 to 19 days). All patients were well on follow-up clinic visits without delayed complications. VATS can be performed safely and effectively in children with stage II empyema, thus avoiding the morbidity of open thoracotomy and decortication. Importantly, early application of VATS significantly relieves patients of unnecessary days of thoracostomy drainage.

Transanal mucosectomy in the treatment of Hirschsprung's disease

BACKGROUND/PURPOSE

Transanal mucosectomy of the aganglionic segment of colon is a critical step in minimally invasive surgery for Hirschsprung's disease. The purpose of this study was to examine the outcome of patients undergoing transanal mucosectomy.

METHODS

From January 1979 to November 1998, 26 patients (ages 25 days to 17 years) underwent transanal mucosectomy for Hirschsprung's disease. Seventeen (65%) had partial transanal mucosectomy (PTM; 1979 to 1998) and 9 (35%) complete transanal mucosectomy (CTM; 1995 to 1998). In PTM, a 2- to 3-cm mucosal dissection was begun 1 cm above the dentate line in conjunction with transabdominal endorectal dissection (modified Soave). In CTM, the entire mucosal dissection was performed transanally as part of a laparoscopically assisted Soave procedure. Results were obtained by chart review and personal communication. Patients were assessed clinically for continence where age appropriate (>3 years) and for development of constipation, postoperative enterocolitis, and anal stricture.

RESULTS

One of 16 (6.2%) of the PTM group was incontinent versus none (4 patients) in the CTM group. Five of 17 (29.4%) of the PTM group were constipated versus 4 of 9 (44.4%) in the CTM group (t test, P = not significant). Postoperative enterocolitis developed in 4 of 17 (23.5%) of the PTM group versus 6 of 9 (66.6%) in the CTM group (t test, P<.05). Three of 6 (50%) of the CTM group versus none in the PTM group required hospitalization for bowel rest, rectal washouts, and antibiotics. All patients were well at the time of the report. Anal stricture was not seen in either group.

CONCLUSIONS

Constipation and postoperative enterocolitis are a significant feature of transanal mucosectomy for Hirschsprung's disease deserving close surveillance, especially in patients in whom the entire mucosal dissection was performed transanally. Continence appears to be satisfactorily preserved from these preliminary results.

Laparoscopic fundoplication in children with previous abdominal surgery

BACKGROUND/PURPOSE

In our institution, many children requiring antireflux surgery for gastroesophageal reflux have had previous abdominal surgery, usually gastrostomy tube or ventriculoperitoneal (VP) shunt placement. The authors review their laparoscopic Nissen fundoplication (LNF) experience in children with previous abdominal surgery assessing surgical outcome.

METHODS

A total of 82 consecutive LNFs performed at our institution between January 1996 and September 1998 were reviewed. Follow-up ranged from 1 month to 32 months (average, 8.9 months). LNF was performed without dividing short gastric vessels (Rosetti modification) through a standard 5-port technique.

RESULTS

A total of 26 of 82 patients (31.7%) had previous abdominal surgery and were divided into 2 groups: gastrostomy (n = 17) and VP shunt (n = 11) with 2 crossovers. A total of 14 of 17 (82.3%) in the gastrostomy group had percutaneous endoscopic gastrostomy (PEG) placement versus 3 of 17 (17.6%) by open technique (open). Four patients in the VP group had multiple surgeries (range, 1 to 10, average, 2.3). LNF was completed in 25 of 26 (96.2%). One operation was converted to an open procedure because of severe adhesions. In 13 of 17 (76.5%) the previous gastrostomy was not taken down. In 4 of 17 (23.5%), the gastrostomy was taken down to complete the procedure: 2 of 3 (66.7%) of the open group versus 2 of 14 (14.3%) of the PEG group. All 11 (100%) of the VP group had successful LNF. Two of 11 (18.2%) had shunt dysfunction at 2 months (shunt infection) and 4 months (clogged distal shunt), respectively. There have been no cases of recurrent reflux, and all gastrostomies and VP shunts were functional at the time of this report.

CONCLUSIONS

Previous abdominal surgery is common in children with gastroesophageal reflux disease requiring an antireflux procedure. The authors conclude from these preliminary results that laparoscopic Nissen fundoplication can be performed safely with minimal morbidity and excellent functional results in children with gastrostomies or ventriculoperitoneal shunts.

Gastroesophageal reflux and Nissen fundoplication following percutaneous endoscopic gastrostomy in children

BACKGROUND

Abnormal gastroesophageal reflux after percutaneous endoscopic gastrostomy is a serious problem in neurologically impaired children. Protective fundoplication has been advocated. Whether esophageal pH monitoring before percutaneous endoscopic gastrostomy will predict later problems with gastroesophageal reflux is unclear.

METHODS

Eighty-five mostly neurologically impaired pediatric patients who underwent percutaneous endoscopic gastrostomy were studied retrospectively regarding complications, success of nutritional rehabilitation, and the incidence of pathologic gastroesophageal reflux. Follow-up period was 1 to 4 years. Twenty-four-hour esophageal pH monitoring was performed in 46 patients before percutaneous endoscopic gastrostomy.

RESULTS

There were no deaths. Two major complications occurred that required surgical intervention, and 14 minor complications occurred related to the procedure. Z-scores for weight increased significantly after percutaneous endoscopic gastrostomy. pH probe results were normal in 22 patients (group 1). Five required medical treatment for gastroesophageal reflux after percutaneous endoscopic gastrostomy, but only 1 (5%) later required Nissen fundoplication. pH probe results were abnormal in 24 patients (group 2). Nineteen required medical therapy for gastroesophageal reflux, and 7 (29%) later needed fundoplication (p < 0.05, incidence of fundoplication group 1 vs. group 2). Improvement in Z-scores was similar in patients requiring and not requiring fundoplication.

CONCLUSIONS

Percutaneous endoscopic gastrostomy is a safe and effective technique for long-term nutritional support in children. Abnormal gastroesophageal reflux is common. Normal findings in an esophageal pH study before percutaneous endoscopic gastrostomy may be predictive of a favorable outcome with respect to gastroesophageal reflux. This is in contrast to patients with abnormal results in pH studies before percutaneous endoscopic gastrostomy of whom a relatively large percentage may later require fundoplication. Improved nutritional status after percutaneous endoscopic gastrostomy does not appear to have an impact on the severity of gastroesophageal reflux.

Cure of hypoglycemic hyperinsulinism by enucleation of a focal islet cell adenomatous hyperplasia

During pancreatectomy for refractory neonatal hyperinsulinemic hypoglycemia, a well-delineated focal adenomatous hyperplasia was enucleated. Intraoperative glucose levels returned to normal and pancreatectomy was averted. Seven months later the child is euglycemic. This experience suggests that during surgery for neonatal refractory hypoglycemia, a focal lesion should be sought, and if found, enucleated, and blood glucose monitored. If the glucose rises to euglycemic levels or above, the child should be monitored clinically. If sustained elevation is not maintained, a search for an additional focal lesion or pancreatectomy should be performed. Saving the pancreas may prevent future development of diabetes mellitus.

Calculous disease of the biliary tract in infants after neonatal extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) can be lifesaving support for neonates with fulminant respiratory failure. In the 121 patients that we have placed on ECMO since 1983, bleeding, infection, and intracranial hemorrhage have constituted most of the major complications. We have also encountered two cases of biliary calculi in post-ECMO infants. The hemolysis, total parenteral nutrition, diuretics, and prolonged fasting associated with ECMO may predispose neonates to early calculous disease of the biliary tract and may require surgical intervention. Evaluation of abdominal pain or jaundice in infants and children who have been supported with ECMO should include examination of the biliary tree. Cholecystectomy should be seriously considered for infants with cholelithiasis.