Potential of biotic inducers on disease severity and variation of Cucumber mosaic cucumovirus in cucumber plants

Abstract

Six bacterial strains (Bacillus subtilis, Bacillus polymyxa, Bacillus circulans, Pseudomonas putida, Pseudomonas fluorescens 2 and Pseudomonas fluorescens 8) and one fungal isolate (Trichoderma harzianum) were tested for their ability to protect Cucumis sativus L. cv. Beith Alpha against the disease development of Cucumber mosaic cucumovirus (CMV). Seed treatment with individual bacterial and fungal liquid cultures significantly and consistently reduced the disease severity (DS) of infected cucumber plants, after 14 days from CMV inoculation onto cotyledons. All seven biotic inducers reduced the CMV infection at the range of 16.6–39% and 0–46.5% under sterilised and non-sterilised soils, respectively. The effect of treatment with each biotic inducer has a significant difference in the percentage of CMV DS. In sterilised soil, B. circulans has a low percentage of DS (42%), while P. fluorescens 8 has a high DS percentage (62.9%). In non-sterilised soil, the low DS percentage was 30% for T. harzianum, while P. putida had the highest DS percentage (70%). On the other hand, CMV variability on Chenopodium amaranticolor revealed that all biotic treatments differed according to the local lesion number, similarity and morphology.