Yang J.H.,Zhenjiang Institute of Agricultural science |
Brannen P.M.,University of Georgia |
Schnabel G.,Clemson University
Plant Disease | Year: 2015
Alternaria rot, caused by Alternaria alternata, was observed in commercial peach orchards in South Carolina. Single-spore isolates formed two phenotypically different culture morphologies on two artificial media. Isolates highly resistant (HR) to boscalid were also HR to penthiopyrad. Among isolates HR and medium resistant (MR) to boscalid and penthiopyrad, we detected isolates that were MR to fluopyram and HR to fluxapyroxad. Sequence analysis of succinate dehydrogenase (sdh) genes sdhB, sdhC, and sdhD revealed that resistant phenotypes were associated with point mutations leading to amino acid substitutions. In particular, H277Y/R in the SDHB and H134R in SDHC were consistently associated with the boscalid HR phenotype. The highest effective concentration that inhibits growth by 50% (EC50) values to penthiopyrad were conferred by H134R and D123E, whereas H134R conferred low resistance and MR to fluxapyroxad. A previously undescribed mutation, G79R, was identified in our collection conferring HR to both boscalid and penthiopyrad. The point mutations associated with highest EC50 values to all four FRAC 7 fungicides were H277L and H134R. The outbreak of Alternaria rot demonstrates that fungicide programs containing “medium to high-risk fungicides” may promote disease outbreaks by secondary pathogens that typically are outcompeted or controlled effectively, while still controlling the primary target disease. © 2015 The American Phytopathological Society.
Fan Z.,Clemson University |
Yang J.-H.,Zhenjiang Institute of Agricultural science |
Fan F.,Huazhong Agricultural University |
Luo C.-X.,Huazhong Agricultural University |
Schnabel G.,Clemson University
Plant Disease | Year: 2015
Field isolates of Alternaria alternata from peach were previously characterized for their sensitivity to succinate dehydrogenase inhibitor (SDHI) fungicides and the underlying molecular basis of resistance was determined. In the present study, we report that isolates resistant to the SDHI fungicide boscalid, regardless of genotype, were also resistant to pyraclostrobin and thiophanate-methyl. Resistance to pyraclostrobin was due to the G143A mutation in cytochrome b and resistance to thiophanate-methyl was due to 167Y in β-tubulin. Representatives of the two most commonly isolated SDHI resistance genotypes, H277Y in sdh subunit B and H134R in sdh subunit C, as well as genotype D123E in sdh subunit D, were selected for fitness evaluations. Genotypes H277Y and H134R suffered no fitness penalties based on mycelial growth on potato dextrose agar, spore production in vitro, osmotic sensitivity, oxidative sensitivity, germination ability, or the ability to cause disease on peach fruit. Hypersensitivity to oxidative stress and weak sporulation was observed only in genotype D123E. No competitive advantage was detected for sensitive isolates over the course of five consecutive transfers on peach fruit when spores were mixed with genotypes H277Y or H134R. Results suggest that, in the absence of fungicide pressure, A. alternata isolates resistant to methyl benzimidazole carbamate, quinone outside inhibitor, and SDHI fungicides carrying the H277Ymutation in SDHB and the H134R mutation in SDHC may effectively compete with the boscalid-sensitive populations. © 2015 The American Phytopathological Society.
Yang M.-M.,Nanjing Agricultural University |
Xu L.-P.,Nanjing Agricultural University |
Xu L.-P.,Wuxi Institute of Termite Control |
Xue Q.-Y.,Nanjing Agricultural University |
And 5 more authors.
European Journal of Plant Pathology | Year: 2012
A total of 1,487 bacterial isolates were obtained from the rhizosphere, phyllosphere, endorhiza and endosphere of field-grown pepper. In a dual assay, 232 isolates displayed the antagonistic activity towards Phytophthora capsici L.; 36. 6 % and 39. 2 % of them were obtained from the rhizosphere and phyllosphere, respectively. 40 of the 232 antagonistic isolates producing inhibition zones of at least 5 mm in diameter were assessed for production of siderophores and chitinase, cellulose, and protease activity. These 40 isolates fell into 15 groups according to 90 % similarity of the banding patterns obtained by amplified ribosomal DNA restriction analysis (ARDRA). Seventeen isolates spanning the 15 groups were evaluated in greenhouse tests for their ability to control Phytophthora blight of pepper. Biocontrol efficacy ranged from 0. 7 % to 92. 3 %, with three isolates (B1301, R98, and PX35) exhibiting maximum ability to reduce the disease severity (83. 5 %, 92. 3 % and 83. 5 %, respectively). Based on 16S rDNA sequencing, these isolates were identified as Bacillus cereus (B1301), Chryseobacterium sp (R98) and Bacillus cereus (PX35). This is the first report that Chryseobacterium sp. (R98) can function as a biocontrol agent of Phytophthora blight. © 2012 KNPV.
Yang J.,Zhenjiang Institute of Agricultural science |
Wu Q.-Y.,Zhenjiang Institute of Agricultural science |
Chen H.-Z.,Zhenjiang Institute of Agricultural science |
Xiao T.,Zhenjiang Institute of Agricultural science |
And 3 more authors.
Chinese Journal of Ecology | Year: 2012
In order to screen a highly-efficient pig manure-decomposing microbial group for fermentation bed, single and mixed fermentation experiments were conducted, with three cellulosedecomposing microbial strains and one yeast strain as test objects, and taking the stock solution of probiotic bacteria and the blank as the controls. Two dominant microbial groups (A and B) were screened, and applied to the pig manure-decomposing test on a simulated fermentation bed. The A (TZ-4+yeast) and B (TZ-4+TZ-15+TZ-16+yeast) had the similar effect in decomposing pig manure, and the effect was better than that of the stock solution of probiotic bacteria. In group B, the TZ-4 and yeast played dominant role. After 47 days decomposition, the bedding with A turned black, the hydrolyzable NH4 +-N content in pig manure decreased from initial 8.31 mg · g-1 to 0.57 mg · g-1, and the seed germination coefficient was the highest (82%). Nearly no stench generated during the whole process of fermentation, and the bed pH remained in an optimum range for microbial growth. It was suggested that the group A could be a promising decomposer agent for the fermentation bed.