Core RNA Interference Genes Involved in miRNA and Ta-siRNA Biogenesis in Hops and Their Expression Analysis after Challenging with Verticillium nonalfalfae

RNA interference is an evolutionary conserved mechanism by which organisms regulate the expression of genes in a sequence-specific manner to modulate defense responses against various abiotic or biotic stresses. Hops are grown for their use in brewing and, in recent years, for the pharmaceutical industry. Hop production is threatened by many phytopathogens, of which Verticillium, the causal agent of Verticillium wilt, is a major contributor to yield losses. In the present study, we performed identification, characterization, phylogenetic, and expression analyses of three Argonaute, two Dicer-like, and two RNA-dependent RNA polymerase genes in the susceptible hop cultivar Celeia and the resistant cultivar Wye Target after infection with Verticillium nonalfalfae. Phylogeny results showed clustering of hop RNAi proteins with their orthologues from the closely related species Cannabis sativa, Morus notabilis and Ziziphus jujuba which form a common cluster with species of the Rosaceae family. Expression analysis revealed downregulation of argonaute 2 in both cultivars on the third day post-inoculation, which may result in reduced AGO2-siRNA-mediated posttranscriptional gene silencing. Both cultivars may also repress ta-siRNA biogenesis at different dpi, as we observed downregulation of argonaute 7 in the susceptible cultivar on day 1 and downregulation of RDR6 in the resistant cultivar on day 3 after inoculation.

Defense Responses, Induced by p-Coumaric Acid and Methyl p-Coumarate, of Jujube ( Ziziphus jujuba Mill.) Fruit against Black Spot Rot Caused by Alternaria alternata

The esterified fraction of jujube ( Ziziphus jujuba Mill.) peel extract showed strong antifungal activity on Alternaria alternata. p-Coumaric acid (pCA) was found to be the most predominant individual phenolic acid that was correlated highly with the antifungal activity of the esterified fraction. Thus, effects of postharvest treatments with pCA and its simplest esterified derivative methyl p-coumarate (MeCA) against black spot rot on jujube fruit caused by A. alternata were investigated. pCA and MeCA strongly suppressed in vitro growth of the fungus and significantly reduced postharvest Alternaria rot on fresh jujubes. Biochemical and transcriptional analysis revealed that pCA and MeCA regulated the expression of some genes encoding antioxidant enzymes and their enzymatic activities, enhanced the phenylpropanoid pathway metabolism, and activated the expression of genes encoding pathogenesis-related proteins. These results suggested that, apart from its direct antifungal activity, pCA and MeCA induced defense responses in jujube fruit against postharvest Alternaria rot.

Tracing Rhizophagus irregularis isolate IR27 in Ziziphus mauritiana roots under field conditions

Arbuscular mycorrhizal fungi (AMF) play a major role as biofertilizer for sustainable agriculture. Nevertheless, it is still poorly documented whether inoculated AMF can successfully establish in field soils as exotic AMF and improve plant growth and productivity. Further, the fate of an exogenous inoculum is still poorly understood. Here, we pre-inoculated two cultivars (Tasset and Gola) of the fruit tree Ziziphus mauritiana (jujube) with the exotic AM fungus Rhizophagus irregularis isolate IR27 before transplantation in the field. In two experiments, tracking and quantification of R. irregularis IR27 were assessed in a 13-month-old jujube and an 18-month-old jujube in two fields located in Senegal. Our results showed that the inoculant R. irregularis IR27 was quantitatively traced and discriminated from native R. irregularis isolates in roots by using a qPCR assay targeting a fragment of the RNA polymerase II gene (RPB1), and that the inoculum represented only fractions ranging from 11 to 15% of the Rhizophagus genus in the two plantations 13 and 18 months after transplantation, respectively. This study validates the use of the RPB1 gene as marker for a relative quantification of a mycorrhizal inoculant fungus isolate in the field.

Changing Host Photosynthetic, Carbohydrate, and Energy Metabolisms Play Important Roles in Phytoplasma Infection

Phytoplasmas parasitize plant phloem tissue and cause many economically important plant diseases. Jujube witches'-broom disease is a destructive phytoplasma disease of Chinese jujube (Ziziphus jujuba). To elucidate the influence of phytoplasma on host photosynthetic, carbohydrate and energy metabolisms, four types of jujube tissues showing disease symptoms with different severity were investigated at the structural, physiological, and molecular levels. Quantitative real-time PCR and high-performance liquid chromatography results showed that the down-regulation of genes related to photosynthesis and the lower contents of chlorophyll in diseased leaves. This clearly inhibited the light-harvesting and photosystem II activity of photosynthesis; however, overexpression of genes related to starch, sucrose and glucose synthesis led to higher contents of these carbohydrates. Meanwhile, transmission electron microscopy images revealed that dense amounts of phytoplasmas accumulated in the sieve elements of diseased petiole phloem, and the structure of the grana and stroma lamellae of chloroplasts in the diseased leaves was destroyed. Phytoplasma infection inhibited photosynthesis and led to abnormal carbohydrate accumulation in the diseased leaves. Furthermore, comparative metabolite analysis indicated that phytoplasma infection also stimulated amino acids and energy metabolisms of the diseased leaves. Continually inhibiting the photosynthetic process and stimulating carbohydrate and energy metabolisms of diseased trees may exhaust their nutrients. Our results highlight the importance of changing host metabolisms during the pathogenic process.

Identification of endophytes with biocontrol potential from Ziziphus jujuba and its inhibition effects on Alternaria alternata, the pathogen of jujube shrunken-fruit disease

Endophytic strains were isolated from different parts of a healthy "Dongzao" jujube (Ziziphus jujuba Mill. 'Dongzao') to find biocontrol agents against jujube shrunken-fruit disease caused by Alternaria alternata. The strains were screened using A. alternata strain CN193 as the target pathogen. The nutrient competition for all isolates was studied using the dual culture, and their inhibitive capability was tested by measuring the inhibition width of filter paper disks with filtrate. Influence of filtrate from the selected strains with strong inhibition of mycelial growth on spore germination was studied with hanging drop method on concavity slides. Colonization in the jujube leaves was assayed using a rifampicin-resistant mutant of strain St-zn-34 as the screening marker. Strains were identified based on their morphological, physiological, and biochemical characteristics, 16S rDNA sequencing, and phylogenetic analysis. A total of 81 endophytic strains were isolated from the stems, leaves, flowers, and fruits of winter jujube. Among these isolates, 14 strains showed strong antagonism against A. alternata. Further study showed that the filtrate of strains St-zn-9 and St-zn-34 could inhibit the mycelial growth of A. alternata, and the widths of their inhibition zone reached 6.14±0.03 mm and 8.27±0.09 mm, respectively. However, strain St-zn-34 showed stronger inhibition on spore germination than strain St-zn-9. St-zn-34 could significantly reduce the spore germination rate of A. alternata, and the spore did not germinate at all or the germ tube was very short. A rifampicin resistant-derivative of wild-type strain St-zn-34, which was designated as St-zn-34r, was obtained by transferring the strains to media with stepwise-increased rifampicin. Colonization assays indicated that St-zn-34r could colonize in jujube leaves, and the population of St-zn-34r was 1.2×103 CFU/g FW after inoculation for 30 days. Except for its salt tolerance, St-zn-34 was the closest to those of Bacillus subtilis. Thus, the strain was identified as B. subtilis.

Metabolic Profiling on Alternaria Toxins and Components of Xinjiang Jujubes Incubated with Pathogenic Alternaria alternata and Alternaria tenuissima via Orbitrap High-Resolution Mass Spectrometry

Xinjiang jujubes (Zizyphus rhamnaceae) are important agro-economical foods with the highest planting area and yields in China; however, black spot disease and contaminated Alternaria toxins have unfortunately caused a decline or loss of jujube nutritional quality in recent years. In this study, we used ultrahigh-performance liquid chromatography coupled to Orbitrap high-resolution mass spectrometry to profile both Alternaria toxins and components in three representative Xinjiang jujubes, Hami Huang, Hetian Jun, and Ruoqiang Hui. Before liquid chromatography-mass spectrometry analysis, jujubes were inoculated with two main pathogens of Alternaria alternata (Aa) and Alternaria tenuissima (At). Different combinations of jujube varieties with pathogenic isolates display different metabolic profiles, as expected. Moreover, four major Alternaria toxins, alternariol, alternariol monomethyl ether, altenuene, and tenuazonic acid, were detected in all samples. The inoculation of both pathogens significantly decreased the levels of nutrients and metabolites in jujube, including four saponins, three organic acids, and three alkaloids, whereas it increased the level of several glycerol phosphates. The flavonoid profiles are diverse. Lastly, inoculation of Aa changes more metabolites in jujubes than At. Our data provide insights to better understand the detrimental contamination of Alternaria pathogens in Xinjiang jujubes and improve food safety of jujubes.

Photosynthetic responses to phytoplasma infection in Chinese jujube

Phytoplasma is one of the most devastating plant pathogens. Jujube witches' broom (JWB) is a typical and highly fatal phytoplasma disease of Chinese jujube (Ziziphus jujuba Mill.), which is widely cultivated in Asia. To further elucidate the mechanism of plant-phytoplasma interaction, we first compared the effects of phytoplasma infection on photosynthetic pigments and activities between a JWB-resistant cultivar (Xingguang) and a susceptible cultivar (Pozao). Total chlorophyll and carotenoid levels were significantly decreased in the susceptible cultivar at later stages of infection, but were remarkably increased in the resistant cultivar at the earlier stages. Compared to uninfected plant, a significant decrease in the main photochemical parameters (Fv/Fm, ΦPSII and qP) was recorded at the initial stages of infection in the resistant cultivar, but occurred at later stages in the susceptible cultivar. Meanwhile, the qRT-PCR results of four key photosynthesis-related genes (ZjGluTR, ZjCBP, ZjRubisco and ZjRCA2) demonstrated that the expression patterns were similar in uninfected cultivars, but up-regulated in resistant cultivar and down-regulated in the susceptible one at 12 wks after grafting inoculation. Collectively, our data indicated that the resistant cultivar 'Xingguang' undergoes a decrease in initial stage (inhibiting phytoplasma multiplication) and then a rapid enhancement of photosynthetic activity (helping jujube recovery) in response to phytoplasma infection, while the susceptible cultivar 'Pozao' displays a later decrease in photosynthetic activity. The novel photosynthetic response pattern of the resistant cultivar may contribute to its stronger immunity to phytoplasma infection, which provides new insights into plant-phytoplasma interactions.

[Kinetic models for determination of yeast in fresh jujube using near infrared spectroscopy]

The objectives of this study were: (1) to optimize a near-infrared (NIR) spectroscopy model for fresh jujube stored at room temperature to predict the quality change (yeast growth), (2) to establish a kinetic model of yeast growth for fresh jujubes at room temperature according to NIR spectroscopy data and storage time, and (3) to predict the shelf life of fresh jujube at room temperature. The Lizao samples of fresh jujubes were adopted as the research object in the study. The NIR spectral data were achieved before yeast infection level measured. In order to optimize the NIR model, the pretreatment techniques such as Savitzky-Golay smoothing (S-G smoothing), multiplicative scatter correction (MSC), first derivative (1-Der) and second derivative (2-Der) were compared with the raw spectra by using a statistical software package (Unscrambler 9.8), and the regression coefficient (RC) method was used to choose the characteristic wavenumber. Multiple linear regression (MLR) was applied as NIR modeling method. According to the predicted yeast infection level using NIR model, the chemical kinetic models of spectral data and storage time at room temperature with zero-order and first-order reaction were established by using a statistical software package (SPSS 18). The shelf life could be predicted based on the chemical kinetic model. The results showed that the characteristic wave numbers of 10 300, 8 330, 6 900, 5 666, 5 150 and 4 060 cm(-1) in the whole near-infrared range with MSC technique could be chosen to model the quality deterioration of fresh jujube at room temperature. The NIR model that produced the best prediction had the form of B = 320.027 - 233.920(chi1) - 206.663(chi2) - 61.584(chi3) - 14.847(chi4) - 2.680(chi5) - 9.131(chi6), where B is yeast value (lg/cfu x g(-1)), chi1-chi6 are absorbance value of characteristic wavenumber. The correlation coefficient of calibration (R(c)) was 0.950, the root mean square error of calibration (RMSEC) was 2. 560, the correlation coefficient of prediction (R(p)) was 0.863, and the root mean square error of prediction (RMSEP) was 2.447. The zero-order reaction kinetic model performed better than the first-order model. The zero-order reaction kinetic model of yeast growth with storage time was predicted by B(t) = 171.395-124.445(chi1) - 109.945(chi2) - 32.763(chi3) - 7.899(chi4) - 1.426(chi5) - 4.857(chi6) + 0.045t with a correlation coefficient of 0.996. Based on the linear correlation between the NIR measurement and storage time, the shelf life of fresh jujube at room temperature was predicted to be 8 days for the yeast infection level less than 10 cfu x g(-1). The study showed that the NIR when combed with kinetic models could be used as a non-destructive, rapid method to detect the yeast growth in fresh jujube, and to predict the shelf life and ensure the quality and safety of fresh jujube.

[Cloning and analysis of tuf and rp gene of the phytoplasma associated with jujube witches' -broom]

OBJECTIVE

Jujube witches' -broom (JWB) is an important plant disease caused by phytoplasma. The major objective of our research was to classify JWB in Beijing and Hebei districts and to provide reference for classification in subgroup level.

METHODS

By use of PCR, the elongation factor Tu (tuf gene) and ribosomal protein (rp) gene of phytoplasma associated with JWB in Beijing and Hebei districts were amplified separately with universal primer pairs fTufu/rTufu and rp(v)F1A/rp(v) R1A. Partial tuf gene and rp gene were sequenced and similarity analysed with other phytoplasmas.

RESULTS

We obtained partial tuf gene sequence (824bp) and complete rp gene (1196bp) from the diseased sample. In tuf gene, JWB in Beijing shared most similarity (92.84%) with Flavescence dorée (FD) phytoplasma (Candidatus Phytoplasma vitis), however, shared a low similarity (57.29%) with JWB in Shaanxi district which had been already reported. The similarity analysis for sequences of rp gene showed a high identity (> 96%) with members of the 16SrV group phytoplasmas. It shared most identity (99.83%) with JWB strain Taishan and Hemp fiber witches' -broom phytoplasma (HFWB) of the 16SrV group.

CONCLUSION

The JWB strains in Beijing and Hebei are members of 16Sr V; JWB in Beijing and Hebei share high similarity, and show a diversity with JWB in Shaanxi.

[Molecular detection and variability of jujube witches'-broom phytoplasmas from different cultivars in various regions of China]

OBJECTIVE

Jujube witches'-broom is an important disease in jujube cultivation areas, which causes serious losses in jujube fruit production. To understand the genetic variability and diversity of jujube witches'-broom phytoplasma population from the different cultivars and various regions of China.

METHOD

We collected 32 samples from 14 cultivars or wild sour jujubes in 7 regions of China and detected them with PCR with the primers R16mF2/R16mR1 for phytoplasma 16S rDNA, SR1/SR for 16S-23SrRNA space region (SR) and FD9f/r for secretion proteins (secY). The direct sequencing of PCR products and sequencing by cloned PCR products were used for sequence polymorphism and phylogenetic analyses by comparison to the databases of known conserved gene sequences.

RESULTS

We detected phytoplasmas by PCR amplification of 16SrDNA from all the diseased jujube samples. All the phytoplasma isolates infected various jujube cultivars belonged to subgroup 16SrV-B of elm yellows group and had closer homology with Bischofia polycarpa witches'-broom and cherry lethal yellows phytoplasmas occurred in China than other 16SrV phytoplasmas in other countries. The sequence polymorphism at different extent in 16SrDNA, SR and secY gene and genetic diversity were revealed in phytoplasma strain population related to different habitats, among which the dominant strains were always detected by the direct sequencing of PCR products in all the diseased areas of China. The degree of variability on secY gene of collected phytoplasma strains was greater than that of 16SrDNA and SR sequences, and some base substitutions could not alter encoded amino acid, however certain single base deletions detected in a Shandong and a Beijing strains may have impact on the gene structure or function.

CONCLUSION

Phytoplasma strains from different cultivars and regions show dramatic genetic diversity. Compared with direct sequencing of PCR products, the sequencing by cloning PCR products was more useful for the displaying of variants and phylogeny in phytoplasma strain population.

[Research on functional diversity of microorganisms on jujube fruit surface in storage]

OBJECTIVE

Disease during storage caused by microbial infection is a serious problem of jujube fruits. The aim of the study was to characterize the microbial diversity in stored jujube fruits.

METHODS

I used Biolog in experiment. The types of micro-plates were Filamentous Fungi micro-plate and Economicmicro-plate.

RESULTS

There was much difference in microbial functional diversity on the surface of stored jujube fruit. The microbial functional diversity of stored 30 days was richer than it of stored 15 days. The diversity, homogeneity and average well color development of jujube used by fruit perservatives were lower than it not used by fruit preservatives. There were six kinds of the characteristic carbon.

CONCLUSION

Our study firstly showed microbial diversity on the surface of stored jujube fruit. Biolog could be applied in the research on microbial functional diversity of fruit surface.

Response of jujube fruits to exogenous oxalic acid treatment based on proteomic analysis

In this study, we found that oxalic acid (OA) at the concentration of 5 mM could delay jujube fruit sene-scence by reducing ethylene production, repressing fruit reddening and reducing alcohol content, which consequently increased fruit resistance against blue mold caused by Penicillium expansum. In order to gain a further understanding of the mechanism by which OA delays senescence and increases disease resistance of jujube fruit, we used a proteomics approach to compare soluble proteome of jujube fruits treated with water or 5 mM OA for 10 min. A total of 25 differentially expressed proteins were identified by using electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-Q-TOF-MS/MS). Among these proteins, alcohol dehydrogenase 1, which plays a direct role in ethanol metabolism, was repressed, and the abundances of three photosynthesis-related proteins was enhanced in jujube fruit after OA treatment. The protein identified as a cystathionine beta-synthase domain-containing protein, which can regulate ethylene precursors, was also induced by OA treatment. The activity of 1-aminocyclopropane-1-carboxylic acid synthase was significantly suppressed in OA-treated jujube fruit. In addition, three proteins related to the defense/stress response were up-regulated by OA, and contributed to the establishment of systemic resistance induced by OA in jujube fruits. These results indicated that OA treatment might affect ethanol and ethylene metabolism, resulting in delaying senescence, and increase resistance of jujube fruits against fungal pathogens.

Antifungal activity of nettle (Urtica dioica L.), colocynth (Citrullus colocynthis L. Schrad), oleander (Nerium oleander L.) and konar (Ziziphus spina-christi L.) extracts on plants pathogenic fungi

Anti-mycotic activity of the ethanol extracts from Nettle (Urtica dioica L.), Colocynth (Citrullus colocynthis L. Schrad), Konar (Ziziphus spina-christi L.) and Oleander (Nerium oleander L.) floral parts were screened in vitro against four important plant pathogenic fungi viz.; Alternaria alternate, Fusarium oxysporum, Fusarium solani and Rizoctonia solani using agar dilution bioassay. Extracts showed antifungal activity against all the tested fungi. Among the plants, Nettle and Colocynth were the most effective against A. alternate and R. solani while Oleander possesses the best inhibition on F. oxysporum and F. solani. Konar was the most effective extract by reducing the growth of Rizoctonia solani than other fungi. These results showed that extracts could be considered suitable alternatives to chemical additives for the control of fungal diseases in plants.

Yeasts and lactic acid bacteria microbiota from masau (Ziziphus mauritiana) fruits and their fermented fruit pulp in Zimbabwe

Masau are Zimbabwean wild fruits, which are usually eaten raw and/ or processed into products such as porridge, traditional cakes, mahewu and jam. Yeasts, yeast-like fungi, and lactic acid bacteria present on the unripe, ripe and dried fruits, and in the fermented masau fruits collected from Muzarabani district in Zimbabwe were isolated and identified using physiological and molecular methods. The predominant species were identified as Saccharomyces cerevisiae, Issatchenkia orientalis, Pichia fabianii and Aureobasidium pullulans. A. pullulans was the dominant species on the unripe fruits but was not isolated from the fermented fruit pulp. S. cerevisiae and I. orientalis were predominant in the fermented fruit pulp but were not detected in the unripe fruits. S. cerevisiae, I. orientalis, P. fabianii and S. fibuligera are fermentative yeasts and these might be used in the future development of starter cultures to produce better quality fermented products from masau fruit. Lactic acid bacteria were preliminary identified and the predominant strains found were Lactobacillus agilis and L. plantarum. Other species identified included L. bifermentans, L. minor, L. divergens, L. confusus, L. hilgardii, L. fructosus, L. fermentum and Streptococcus spp. Some of the strains of LAB could also potentially be used in a mixed-starter culture with yeasts and might contribute positively in the production of fermented masau fruit products.

Supercritical fluid extraction and quantification of aflatoxins in Zizyphi Fructus by liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

An integrated method combining supercritical fluid extraction (SFE) with liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI-MS/MS) was developed and successfully applied to quantify aflatoxins (AFs) in Zizyphi Fructus (fruits of Zizyphus jujube), a traditional Chinese medicine. To minimize the potential interferences caused by the complex matrix in Zizyphi Fructus, a SFE pretreatment was performed. In addition, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) spectra were also compared. The results showed that the calibration curves of AFB(1), AFB(2), AFG(1), and AFG(2) were all linear over the range of concentration from 1 to 50 ng/g, the squared correlation coefficients (r(2)) were over 0.995, and the detection limits of the method were between 0.17 and 0.32 ng/g. It showed high recovery and good precision in quantitating AFs in Zizyphi Fructus without further clean-up. Further, fragmentation pathways of protonated AFs in APCI-MS/MS were clearly proposed which could predict the existence of AFB or AFG series. To test the empirical validity of the proposed methodology in this paper, eight random samples of Zizyphi Fructus collected from supermarkets and traditional Chinese medicine stores in different geographical areas of Taiwan were analyzed. The results indicated that low levels of AFs were detected in only one of them.

Metschnikowia sinensis sp. nov., Metschnikowia zizyphicola sp. nov. and Metschnikowia shanxiensis sp. nov., novel yeast species from jujube fruit

Eight yeast strains were isolated from jujube fruit surfaces collected in Shanxi and Shandong Provinces, China. All eight strains produced needle-shaped ascospores under suitable conditions. Three separate groups, representing three novel species in the genus Metschnikowia, were recognized by sequence comparisons of the 26S rDNA D1/D2 domain and internal transcribed spacer (ITS) region. The names Metschnikowia sinensis sp. nov. (type strain XY103(T)=AS 2.3110(T)=CBS 10357(T)), Metschnikowia zizyphicola sp. nov. (type strain XY201(T)=AS 2.3111(T)=CBS 10358(T)) and Metschnikowia shanxiensis sp. nov. (type strain XY801(T)=AS 2.3112(T)=CBS 10359(T)) are proposed for the three novel species. Phylogenetic analysis of the 26S rDNA D1/D2 domain sequence showed that these three novel species are clustered in a clade together with the previously described species Metschnikowia fructicola, Metschnikowia andauensis, Metschnikowia pulcherrima and Metschnikowia chrysoperlae.

Synergistic effects of combining biocontrol agents with silicon against postharvest diseases of jujube fruit

The synergistic effects of biocontrol yeasts Cryptococcus laurentii and Rhodotorula glutinis combined with silicon (Si) against Alternaria alternata and Penicillium expansum molds were investigated in jujube fruit (Chinese date, Zizyphus jujuba) stored at 20 and 0 degrees C, respectively. Combinations of C. laurentii and R. glutinis at 5 x 10(7) cells/ml with 2% Si was most effective in controlling the diseases caused by A. alternata and P. expansum on jujube fruit stored at 20 degrees C. When fruits were stored at 0 degrees C, combining C. laurentii and R. glutinis with Si was as effective against P. expansum as was Si or the yeasts applied alone and was more effective in controlling A. alternata. Si may have a fungistatic effect by directly inhibiting pathogen growth, but it did not greatly influence the growth of the antagonists.

Enhancement of biocontrol activity of yeasts by adding sodium bicarbonate or ammonium molybdate to control postharvest disease of jujube fruits

AIMS

To assess the potential of sodium bicarbonate and ammonium molybdate as additives in enhancing the biocontrol efficacy of Rhodotorula glutinis and Cryptococcus laurentii against blue mould in jujube fruits.

METHODS AND RESULTS

Two yeasts at a concentration of 107 CFU ml-1, in combination with 238 mmol l-1 sodium bicarbonate or 15 mmol l-1 ammonium molybdate, showed a significant inhibition effect on blue mould of jujube fruits stored at 20 degrees C for 5 days. The colonizing ability of the yeasts in wounded sites was significantly decreased in the presence of ammonium molybdate.

CONCLUSIONS

Combining R. glutinis or C. laurentii with sodium bicarbonate or ammonium molybdate provided a more effective control of postharvest disease than using the antagonistic yeasts or the chemicals alone.

SIGNIFICANCE AND IMPACT OF THE STUDY

The addition of sodium bicarbonate or ammonium molybdate reduced the number of antagonists required to efficiently control disease of postharvest fruits, which could result in the reduction of costs.

'Candidatus phytoplasma ziziphi', a novel phytoplasma taxon associated with jujube witches'-broom disease

Phylogenetic relationships of five jujube witches'-broom (JWB) phytoplasma isolates from four different districts, and other phytoplasmas, were investigated by 16S rDNA PCR amplification and sequence analysis. The 16S rDNA sequences of any pair of the five isolates of JWB phytoplasmas were > 99.5% similar. The JWB phytoplasma 16S rDNA sequences were most closely related to that of the elm yellows (EY) phytoplasma in 16S-group VIII. Phylogenetic analysis of the 16S rDNA sequences from the JWB phytoplasma isolates, together with sequences from most of the phytoplasmas archived in GenBank, produced a tree in which the JWB isolates clustered as a discrete subgroup. The uniqueness of the JWB phytoplasma appears to be correlated with a specific insect vector (Hishimonus sellatus) and the host plant (Zizyphus jujuba), or with a specific geographical distribution. The unique properties of the JWB phytoplasma sequences clearly indicate that it represents a novel taxon, 'Candidatus Phytoplasma ziziphi'.