Distribution and Virulence Phenotypes of Heterodera glycines in Missouri

Characterization of Virulence Phenotypes of Heterodera glycines during 2020 in Indiana

The soybean cyst nematode (SCN, Heterodera glycines) is the most yield-limiting pathogen of soybean in the US. This study was carried out in order to provide updated information on SCN virulence phenotypes in Indiana. A total of 124 soil samples were collected from soybean fields in 2020 and all of them tested positive for SCN. The virulence phenotypes of 42 representative SCN populations were determined with seven soybean indicator lines using the standard HG type test. The most predominant HG types were 2.5.7 and 1.2.5.7, which accounted for 64% and 14% of the SCN populations tested, respectively. None of the SCN populations tested were rated as HG type 0, compared with 28% of the populations in a previous survey in Indiana during 2006-2008. Nearly 88% of the SCN populations evaluated in this study overcame the resistance provided by PI 88788, which is the most common source of resistance in soybean, up from 56% in the 2006-2008 survey. Approximately 14% of SCN populations tested were virulent to PI 548402 (Peking), in contrast to 0% in the 2006-2008 survey. This study reveals a trend of increasing virulence of SCN populations to resistant sources of soybean in Indiana. The results highlighted the importance of rotating soybean varieties with different types of resistance and identifying new sources of resistance for sustainable management of SCN.

Characterization of Virulence Phenotypes of Soybean Cyst Nematode (Heterodera glycines) Populations in North Dakota

Soybean cyst nematode (SCN; Heterodera glycines) continues to be the greatest threat to soybean production in the United States. Because host resistance is the primary strategy used to control SCN, knowledge of SCN virulence phenotypes (HG types) is necessary for choosing sources of resistance for SCN management. To characterize SCN virulence phenotypes in North Dakota, a total of 419 soybean fields across 22 counties were sampled during 2015, 2016, and 2017. SCN was detected in 42% of the fields sampled, and population densities in these samples ranged from 30 to 92,800 eggs and juveniles per 100 cm3 of soil. The SCN populations from some of the infested fields were virulence-phenotyped with seven soybean indicator lines and a susceptible check ('Barnes') using the HG type tests. Overall, 73 SCN field populations were successfully virulence-phenotyped. The HG types detected in North Dakota were HG types 0 (frequency rate: 36%), 7 (27%), 2.5.7 (19%), 5.7 (11%), 1.2.5.7 (4%), and 2.7 (2%). However, before this study only HG type 0 was detected in North Dakota. The designation of each of these HG types detected was also validated by repeating the HG type tests for 33 arbitrarily selected samples. This research for the first time reports several new HG types detected in North Dakota and confirms that the virulence of SCN populations is shifting and overcoming resistance, highlighting the necessity of using different resistance sources, rotating resistance sources, and identifying novel resistance sources for SCN management in North Dakota.

Characterization of Virulence Phenotypes of Heterodera glycines in Heilongjiang, Northeast China

Knowledge about virulent phenotypes of Heterodera glycines Ichinohe, 1952 (soybean cyst nematode, SCN) is essential for breeding resistant cultivars and managing this nematode. Heilongjiang Province is the major soybean-producing region in China. SCN has been reported in 63 regions in Heilongjiang Province. To determine the prevalence and virulence of phenotypes of SCN, 112 soil samples were collected from soybean fields throughout the province in 2015. SCN was detected in 62 (55.4%) of these samples, with population densities ranging from 150 to 41,750 eggs and juveniles per 100 cm3 of soil. Eleven HG types, namely HG 0, 1.2.3.5.7, 1.2.3.7, 1.3.4.7, 1.3.7, 2, 2.5.7, 2.7, 6, 6.7, and 7, were detected. The percentages of SCN populations with female indices greater than 10 ranged from 4.8% for PI 437654 to 64.5% for PI 548316. This is the first report of seven of the HG types from Heilongjiang. These results provide guidance for breeding efforts and control strategies to combat SCN.

Developing Public-Private Partnerships in Plant Pathology Extension: Case Studies and Opportunities in the United States

Public-private partnerships (PPPs) can be an effective and advantageous way to accomplish extension and outreach objectives in plant pathology. The greatest opportunities for extension-focused PPPs may be in response to large-scale or emerging disease management concerns or in addressing complex issues that impact agriculture, such as climate change, digital technology, and public perception of science. The most fertile ground for forming PPPs is where the needs and strengths of the public and private sectors are complementary. Developing PPPs depends as much on professional relationships as on technical skills or contracts. Defining and making room for the success of all partners, identifying and addressing barriers to success, and earning and maintaining trust are components that contribute to the effectiveness of PPPs. Case studies in plant pathology demonstrate the positive impact PPPs can have on partners and stakeholders and provide guidance on the formation of PPPs in the future.

Dynamics of Population Density and Virulence Phenotype of the Soybean Cyst Nematode as Influenced by Resistance Source Sequence and Tillage

The soybean cyst nematode (SCN), Heterodera glycines, is the most damaging pathogen of soybean. Use of resistant cultivars is an effective strategy to manage SCN, but it also selects for virulent populations over time. A 12-year field experiment was initiated in 2003 to study how tillage and 11 different sequences of four cultivars impact SCN population dynamics and virulence. An SCN-susceptible cultivar and three resistant cultivars (R1, R2, and R3 derived from cultivars PI 88788, Peking, and PI 437654, respectively) were used. Tillage had minimal effect on SCN population density. Compared with no till, conventional tillage resulted in a faster increase of SCN virulence to Peking when the SCN was selected by R2 and virulence to PI 88788 by R3. Among the three SCN-resistant cultivars, R1 supported the greatest population density, R2 supported intermediate population density, and R3 supported the least SCN population density. The SCN populations selected by R1 overcame the resistance in PI 88788 but not in Peking and PI 437654. R2 selected SCN populations that overcame the resistance in Peking but not in PI 88788 and PI 437654. In contrast, R3 selected SCN populations that overcame both PI 88788 and Peking sources of resistance. There was no increase of virulence to PI 437654 in any cultivar sequence. R1 in rotation with R2 or R3 had a negative effect on female index on Peking. Susceptible soybean reduced SCN virulence to Peking, indicating that there was fitness cost of the Peking virulent SCN type. These results suggest that rotation of Peking with PI 88788 is a good strategy for managing the SCN, and susceptible cultivar and no till may reduce SCN virulence selection pressure in some rotations.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Survey of Heterodera glycines Population Densities and Virulence Phenotypes During 2015-2016 in Missouri

The soybean cyst nematode (SCN), Heterodera glycines, is one of the most important pathogens of soybean. Periodic monitoring of SCN population densities and virulence phenotypes is necessary for developing management strategies utilizing resistant cultivars, the primary strategy used to combat this pest. Therefore, we conducted a statewide survey of Missouri to determine SCN population densities and virulence phenotypes during 2015-2016 and compared these results with a similar survey conducted in 2005. SCN population densities were determined for 393 soil samples representing 74 soybean-producing counties across eight geographical regions of Missouri. Eighty-eight percent of samples tested positive for SCN, up from 50% in 2005, and population densities ranged from 125 to 99,000 eggs per 250 cm3 of soil. The virulence phenotypes of 48 SCN populations also were determined. For this, female indices (FI) were calculated by dividing the mean number of females that develop on the roots of a set of resistant soybean indicator lines by the mean number of females that develop on the roots of susceptible cultivar Lee74 after 30 days in the greenhouse then multiplying by 100 to obtain a percentage. Notably, all SCN populations evaluated during 2015-2016 had a FI > 10 on PI 88788, the most widely used source of resistance in Missouri, in contrast to 78% in 2005. Moreover, 50% of these populations had a FI > 50 on PI 88788, up from 16% in 2005. Forty-three percent of populations tested also had a FI > 10 on Peking, the second most common source of resistance by farmers. Our results show that over the last decade, SCN has become more prevalent in Missouri fields. Additionally, the percentage of individuals within SCN field populations that are virulent on PI 88788 and Peking has markedly increased. The results stress the importance of rotating cultivars with different types of resistance when using resistant cultivars to manage SCN.

Accessions of Perennial Glycine Species With Resistance to Multiple Types of Soybean Cyst Nematode (Heterodera glycines)

Soybean cyst nematode (SCN; Heterodera glycines; HG) is a widely occurring and damaging pathogen that limits soybean production. Developing resistant cultivars is the most cost-effective method for managing this disease. Genes conferring SCN resistance in soybean have been identified; however, there are SCN populations that overcome known resistance genes. In order to identify additional sources of resistance and potentially new resistance genes, 223 plant introductions (PIs) of G. tomentella and 59 PIs of 12 other perennial Glycine species were inoculated with HG Types 0, HG 2, and HG 1.2.3, and then 36 PIs out of this set were further evaluated with HG Type 1.2.3.4.5.6.7, a population that overcomes all the resistance genes in soybean. Of 223 G. tomentella PIs evaluated, 86 were classified as resistant to three HG types, 69 as resistant to two HG types, and 22 as resistant to one HG type. Of the other 12 perennial Glycine species, all PIs of G. argyrea and G. pescadrensis were resistant to all three HG types. Of the 36 PIs challenged with HG Type 1.2.3.4.5.6.7, 35 were resistant with 16 showing no cyst reproduction. Our study confirms that there are high levels of resistance to SCN among the perennial Glycine species. This represents an untapped resource for use in genetic studies and for improving resistance to SCN in soybean.

Determination of Heterodera glycines Virulence Phenotypes Occurring in South Dakota

The soybean cyst nematode (SCN), Heterodera glycines, is the most important yield-limiting pathogen of soybean in the United States. In South Dakota, SCN has been found in 29 counties, as of 2016, and continues to spread. Determining the virulence phenotypes (HG types) of the SCN populations can reveal the diversity of the SCN populations and the sources of resistance that would be most effective for SCN management. To determine the HG types prevalent in South Dakota, 250 soil samples were collected from at least three arbitrarily selected fields in each of the 28 counties with fields previously found to be infested with SCN. SCN was detected in 82 fields (33%), and combined egg and juvenile counts ranged from 200 to 65,200 per 100 cm³ of soil. Eggs and juveniles were extracted from each soil sample and were used to infest seven SCN HG type test indicator soybean lines and 'Williams 82' as the susceptible check. A female index (FI) was calculated based on the number of females found on each indicator line relative to those on the susceptible check. A FI equal to or greater than 10% in any line was assigned as that HG type. Out of 73 SCN populations for which HG type tests were done, 63% had FI ≥10% on PI 548316 (indicator line #7), 25% on PI 88788 (#2), 19% on PI 209332 (#5), 7% on PI 548402 (#1), 4% on PI 90736 (#3), and 4% on PI 89722 (#6). None of the SCN populations had FI ≥10% on PI 437654 (indicator line #4). The most prevalent HG types were 0, 2.5.7, and 7. These accounted for 81% of all the HG types determined for the samples tested. HG types with ≥10% reproduction on indicator lines PI 88788, PI 209332, and PI 548317 were most prevalent in the soil samples tested, suggesting that the use of these sources of resistance for developing SCN resistant cultivars should be avoided. For sustainable SCN management, use of resistant cultivars should be rotated with nonhost crops and cultivars with different sources of resistance.

QTL underlying resistance to two HG types of Heterodera glycines found in soybean cultivar 'L-10'

BACKGROUND

Resistance of soybean (Glycine max L. Merr.) cultivars to populations of cyst nematode (SCN; Heterodera glycines I.) was complicated by the diversity of HG Types (biotypes), the multigenic nature of resistance and the temperature dependence of resistance to biotypes. The objective here was to identify QTL for broad-spectrum resistance to SCN and examine the transcript abundances of some genes within the QTL.

RESULTS

A Total of 140 F(5) derived F(7) recombinant inbred lines (RILs) were advanced by single-seed-descent from a cross between 'L-10' (a soybean cultivar broadly resistant to SCN) and 'Heinong 37' (a SCN susceptible cultivar). Associated QTL were identified by WinQTL2.1. QTL Qscn3-1 on linkage group (LG) E, Qscn3-2 on LG G, Qscn3-3 on LG J and Qscn14-1 on LG O were associated with SCN resistance in both year data (2007 and 2008). Qscn14-2 on LG O was identified to be associated with SCN resistance in 2007. Qscn14-3 on LG D2 was identified to be associated with SCN resistance in 2008. Qscn14-4 on LG J was identified to be associated with SCN resistance in 2008. The Qscn3-2 on LG G was linked to Satt309 (less than 4 cM), and explained 19.7% and 23.4% of the phenotypic variation in 2007 and 2008 respectively. Qscn3-3 was less than 5 cM from Satt244 on LG J, and explained 19.3% and 17.95% of the phenotypic variations in 2007 and 2008 respectively. Qscn14-4 could explain 12.6% of the phenotypic variation for the SCN race 14 resistance in 2008 and was located in the same region as Qscn3-3. The total phenotypic variation explained by Qscn3-2 and Qscn3-3 together was 39.0% and 41.3% in 2007 and 2008, respectively. Further, the flanking markers Satt275, Satt309, Sat_350 and Satt244 were used for the selection of resistant lines to SCN race 3, and the accuracy of selection was about 73% in this RIL population. Four genes in the predicted resistance gene cluster of LG J (chromosome 16) were successfully cloned by RT-PCR. The transcript encoded by the gene Glyma16g30760.1 was abundant in the SCN resistant cultivar 'L-10' but absent in susceptible cultivar 'Heinong 37'. Further, the abundance was higher in root than in leaf for 'L-10'. Therefore, the gene was a strong candidate to underlie part of the resistance to SCN.

CONCLUSIONS

Satt275, Satt309, Sat_305 and Satt244, which were tightly linked to the major QTL for resistance to SCN on LG G and J, would be candidates for marker-assisted selection of lines resistant to the SCN race 3. Among the six RLK genes, Glyma16g30760.1 was found to accumulate transcripts in the SCN resistance cultivar 'L-10' but not in 'Heinong 37'. The transcript abundance was higher in root than in leaf for L-10.

Variability in Distribution and Virulence Phenotypes of Heterodera glycines in Missouri During 2005

The soybean cyst nematode, Heterodera glycines, is a serious economic threat to soybean producers in Missouri. Periodic monitoring for the presence, population densities, and virulence phenotypes of H. glycines is essential for determining crop losses and devising management strategies implementing the use of resistant cultivars. A survey using area-frame sampling was conducted to determine the distribution and virulence phenotypes of H. glycines in Missouri during 2005. Two samples from each of 125 fields representing eight geographical regions of Missouri were collected; 243 samples were processed for extraction of cysts and eggs. In all, 49% of samples had detectable cyst nematode populations, which ranged from 138 to 85,250 eggs per 250 cm³ of soil. Race and H. glycines type tests were conducted on populations from 45 samples. Nearly 80% of the populations that were tested, irrespective of the region, were virulent on the indicator line plant introduction (PI) 88788, which is the source of resistance for most H. glycines-resistant cultivars. More than 70% of populations could reproduce on the indicator lines PI 88788, PI 209332, and PI 548316 (Cloud), indicating that soybean cultivars with resistance derived from these sources need to be carefully monitored and used only in rotation with nonhost crops and soybean cultivars with resistance from other sources. Approximately one-third of the populations, primarily in the southern regions of Missouri, could reproduce on PI 548402 (Peking), another common source of resistance. Fewer than 10% of the populations could reproduce on PI 90763, PI 437654, PI 89772, or PI 438489B, suggesting that these sources of resistance should be used in soybean breeding programs to develop H. glycines-resistant soybean cultivars.

Resistance of Soybean Cultivars to Field Populations of Heterodera glycines in North Carolina

The soybean cyst nematode (SCN), Heterodera glycines, is the most important pathogen of soybean, Glycine max, in North Carolina. Cultural practices are the most effective means of managing this pathogen because a majority of cultivars are susceptible to the races of this nematode that predominate in the state. Resistant and susceptible cultivars were evaluated in 14 H. glycines-infested fields from 1992 to 1999. Resistance in cvs. Hartwig and Delsoy 5710, and line S92-1603 derived from plant introduction (PI) 437654, was highly effective against all populations of H. glycines evaluated in these experiments. Numbers of cysts (cysts and white females) per three plants 28 days after planting and final egg population densities (Pf) were lower than on other cultivars evaluated. Cultivars with SCN resistance derived from PI 90763 were moderately resistant in many of the test fields, but cultivars with Peking-derived resistance were effective at only two locations. Some cultivars with resistance derived from PI 88788 were highly to moderately resistant to races 9 or 14 of SCN, but were not consistently effective against other populations. Hartwig and Delsoy 5710 had low SCN reproductive factors (Rf = egg density at harvest/mean egg density at planting for site) of 0.16 and 0.23 compared with an Rf of 1.9 and 2.19 on the susceptible cvs. Essex and Hutcheson, respectively. In contrast, the Rf on cultivars derived from Peking generally was greater than on susceptible cultivars. Resistant cvs. Hartwig and Delsoy 5710 generally yielded more than susceptible cultivars or cultivars derived from other sources of resistance. The initial inoculum level (Pi) was negatively correlated with soybean seed yield, but cysts 28 days after planting proved to be better at predicting seed yield than Pi. Due to the genetic diversity of H. glycines populations with regard to the ability to parasitize resistant cultivars, cultivars with resistance derived from PI 437654 or other genotypes are needed to manage this nematode in North Carolina.