Abstract
A study of molecular variation among Botrytis spp., the causal pathogen of scape and umbel blights of onion, as well as the biocontrol of the virulent pathogen using Bacillus subtilis PHYS7 under greenhouse conditions was carried out. Twenty-three isolates of Botrytis spp. were recovered from onion plants showing umbel blight symptoms. They were able to infect onion plants with varied severity. All Botrytis spp. produced cellulases; owever,
almost all of them produced pectinase. The highest activities of cellulases and pectinase were achieved by B. allii PHYOA1; however, B. cinerea PHYOC3 showed a high activity of cellulases but it failed to produce pectinase. the genetic variability among the pathogens was assessed by random amplified polymorphic DNA (RAPD) markers, using 5 random 10-mer primers: OPA03, OPA05, OPA06, OPI09, and OPW15. The results showed that 50 DNA bands
ranging from 100 bp (OPA03) to 1600 bp (OPA05) were generated by the 5 primers that differentiated 9 isolates of Botrytis spp. The dual culture test showed that Bacillus subtilis PHYS77 and PHYS78 had a high ntagonistic
potentiality against the pathogen and involved in 60–62% reduction in its growth. Application of Ridomil Gold MZ and Bacillus subtilis PHYS77 on onion plants, 2 days after or before infection with the pathogen, significantly reduced the disease severity than the control. The study approved the molecular tool as a reliable and quick method to differentiate among the virulent and non-virulent strains of Botrytis spp. The application of B. subtilis PHYS77 as an effective biocontrol agent in the management of the onion blight disease can be recommended.