Antagonism of Paenibacillus lentimorbus to Botryosphaeria dothidea and biological control of panicle and shoot blight of pistachio

A potential microbial fungicide, Paenibacillus lentimorbus isolate CBCA-2, against Botryosphaeria dothidea, the pistachio panicle and shoot blight fungus, was obtained from healthy pistachio leaves by both in vitro and in vivo screening techniques. CBCA-2 caused 100% inhibition of pycnidiospore germination after 24 h incubation at 25 C. Malformation of pycnidiospores and hyphae, and lysis and swollen pycnidiospores of B. dothidea occurred in the presence of cell suspensions of CBCA-2. Among the five media tested, nutrient yeast dextrose broth significantly increased the production of antifungal compounds. Application of culture filtrates of CBCA-2 suppressed disease on detached pistachio leaves, but washed bacterial cells did not inhibit lesion development. Development of lesions on excised dormant stems was inhibited only when the culture filtrate was applied before fungal inoculation. Survival of the CBCA-2 after treatment with azoxystrobin (Abound), benomyl (Benlate), tebuconazole (Elite), propiconazole (Break), or trifloxystrobin (Flint) at the highest recommended concentration was not affected, but survival was affected by iprodione (Rovral). Spraying a suspension of CBCA-2 on pruning wounds before inoculation with pycnidiospores of B. dothidea significantly reduced infection compared with the unsprayed, inoculated controls.