Transmission of seed-borne infection of muskmelon by Didymellabryoniae and effect of seed treatments on disease incidenceand fruit yield

摘要

Infected muskmelon plants were collected and a fungus was isolated during field survey of muskmelon conducted in 4th, 5th, and 6thagroclimatic zones of Karnataka state. The pathogen was identified as Didymella bryoniae upon incubation on potato dextrose agar plates.The pathogen causes gummy stem blight disease in muskmelon. Spore concentration of 12 x 10~5 ml~(-1) was found to be very effective in rees-tablishment of the pathogen upon artificial inoculation. The pathogen was located both externally and internally on the seed. Naturallyinfected seeds were subjected to transmission studies in vitro and in vivo. Four fungicides and two biological agents were evaluated for theirefficacy against gummy stem blight disease incidence and fruit yield in field conditions. In water agar, primary seedling infection occurred onhypocotyls and cotyledons while pycnidia on ungerminated seeds and stunted seedling were also noticed due to severity of the infection. Typ-ical symptoms expressed from 35 to 67 days after sowing until harvest experimentally, the fungus was more prevalent at the collar region ofthe plant. Mean disease incidence from all the cultivars significantly reduced except Bavistin (Carbendazim 50% WP), among which fungi-cides Dithane M-45 0.2% (Mancozeb 75% WP) and Wanis 0.3% significantly (P = 0.001) reduced the disease incidence where only 10.2 and13.0%, disease was recorded, respectively and severity of gummy stem blight compared with Captaf 0.3% (Captan 50% WP) with 24.2% dis-ease, whereas Bavistin (Carbendazim 50%) WP) seed treatment was par with the control. Among antagonists, Pseudomonas fluorescensapplied as pure culture (1 x 10~8 cfuml~(-1)) and formulation of (26 x 10~7cfug~(-1)) at the rate of 8 and l0gkg~(-1) significantly (P = 0.001) reducedthe disease incidence, which showed 17.7, 21.5, and 20.5%, disease respectively. On the contrary pure culture of Trichoderma harzianum(1 x 10~8cfuml~(-1)) recorded 18.2% D. bryoniae incidence followed by its formulation (21 x 10~7cfug~~(-1)), which recorded 24.0 and 21.2% diseasein 8 and lOgkg~(-1), respectively. Mean fruit weight from all the tested cultivars were increased at higher concentration (0.3%) by as much as265 g in Dithane M-45, 154 g in Captaf and only 55 g in Bavistin treated seeds, while Wanis treatment resulted in decreased fruit weight whencompared to untreated control. Seeds treated with P. fluorescens both as pure culture and formulation significantly (P 0.001) effective inincreasing the fruit yield by 370, 350, and 363 g, respectively. Though slight decrease in the yield was noticed in T. harzianum both as pure cul-ture and formulation were significantly (P = 0.001) effective in increasing the fruit yield. However, both P. fluorescens and T. harzianum treat-ments showed significant increase in fruit weight over fungicides and untreated seeds.