Diversity of culturable microorganisms in pathosphere of Plasmopara viticola and screening of potential biocontrol strains

Abstract:

[Objective] To investigate the diversity of bacteria and fungi in the pathosphere of Plasmopara viticola and screen out the strains with potential biocontrol effects on grape downy mildew. [Methods] The leaves infected by P. viticola were collected from seven representative grape-producing regions in northern and southern China in two consecutive years. The collected leaves were cultured in a humid environment, and the newly growing downy mildew was aseptically picked by forceps to prepare the sporangial suspensions of P. viticola. The strains were isolated by the conventional culture method and identified based on the morphological characteristics, BOX-PCR fingerprints, and molecular sequences. Furthermore, the clustering analysis of different strains was conducted. Sporangial inhibition was tested with equal volumes of strain suspension or fermentation mixed with the sporangial suspension of P. viticola, and the control effects of isolates and their sterile fermentation against grape downy mildew were tested on detached grape leaves. [Results] A total of 90 bacterial strains and 110 fungal strains were isolated, belonging to eight bacterial genera and 14 fungal genera, respectively. The pathosphere of P. viticola in the same province and the same year exhibited similar microbial community composition. Notably, strains of Pseudomonas spp. and Cladosporium spp. exhibited stable populations on grape cultivars collected from different provinces. A majority (over 80.0%) of strains with stable populations in two consecutive years demonstrated significant biocontrol effects against grape downy mildew. Six Acremonium strains with ubiquitous distribution demonstrated the biocontrol effect up to 100.0%. Sterile fermentation of the fungal strains Aspergillus niger NX2F, Thecaphora amaranthi BJ1G, and Rhizopus stolonifer BM1L showed the control effects of 100.0% against grape downy mildew. [Conclusion] The culturable bacterial and fungal communities in the pathosphere of P. viticola were mainly affected by geographical factors in different provinces, and most of the culturable microorganisms presented stable and strong biocontrol effects on grape downy mildew. To the best of our knowledge, it is the first comprehensive report that Acremonium spp. were epibiotic fungi and consistently associated with P. viticola, providing rich and valuable biocontrol resources for grape downy mildew.