Differentiation of Verticillium dahliae populations on the basis of vegetative compatibility and pathogenicity on cotton

Abstract Complementary auxotrophic nitrate-nonutilizing (nit) mutants were used to investigate vegetative compatibility within 27 strains of Verticillium dahliae isolated from several hosts originating from Africa, Asia, Europe and the United States. Using about 500 nit mutants generated from these strains, three vegetative compatibility groups, 1 , 2 and 4, were identified. Simultaneously, virulence of each strain was assessed on cultivars of Gossypium hirsutum, G. barbadense and G. arboreum, based upon Foliar Alteration Index (FAI) and Browning Index (BI) estimation. The strains in VCGl were of both the cottondefoliating pathotype and race 3 (on cotton) but were non pathogenic on tomato; those in VCG2 and VCG4 were of the nondefoliating pathotype and belonged to different races on cotton and on tomato. Hyaline mutants deriving from parental wild-type strain showed differences in pathogenicity but were always assigned to the parental VCG. A relationship was established between VCGs and the taxonomic position of host plants. Data from nit pairings indicated that the sub-populations of V. dahliae (VCGS) may not be completely isolated genetically. .

Role of the cyclic lipopeptide massetolide A in biological control of Phytophthora infestans and in colonization of tomato plants by Pseudomonas fluorescens

Pseudomonas strains have shown promising results in biological control of late blight caused by Phytophthora infestans. However, the mechanism(s) and metabolites involved are in many cases poorly understood. Here, the role of the cyclic lipopeptide massetolide A of Pseudomonas fluorescens SS101 in biocontrol of tomato late blight was examined. Pseudomonas fluorescens SS101 was effective in preventing infection of tomato (Lycopersicon esculentum) leaves by P. infestans and significantly reduced the expansion of existing late blight lesions. Massetolide A was an important component of the activity of P. fluorescens SS101, since the massA-mutant was significantly less effective in biocontrol, and purified massetolide A provided significant control of P. infestans, both locally and systemically via induced resistance. Assays with nahG transgenic plants indicated that the systemic resistance response induced by SS101 or massetolide A was independent of salicylic acid signalling. Strain SS101 colonized the roots of tomato seedlings significantly better than its massA-mutant, indicating that massetolide A was an important trait in plant colonization. This study shows that the cyclic lipopeptide surfactant massetolide A is a metabolite with versatile functions in the ecology of P fluorescens SS101 and in interactions with tomato plants and the late blight pathogen P. infestans

The Top 10 oomycete pathogens in molecular plant pathology

Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens which threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant-pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. This article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.Keywords: microbiology, diversity, genomics, oomycetes plant patholog