LAUSR

Abstract Bud necrosis disease (BND) caused by watermelon bud necrosis orthotospovirus (WBNV), has emerged a major deterrent in watermelon cultivation in Indian subcontinent. In the present study, identification of resistance source against WBNV under field and glasshouse conditions was carried out, wherein a total of the 45 watermelon genotypes were evaluated during 2010–11 and 2011–12 crop seasons in a randomized block design with three replications each. Field evaluation was carried out using 0–4 disease rating scale. Of the 45 watermelon genotypes, a wild relative, Citrullus colosynthis showed highly resistant (HR) reaction against BND during both the crop seasons (absorbance @ 405 nm: 0.07-0.28). While, five genotypes viz., PWMH-1, PWMH-2, PWMH-3, PWMH-12 and PWMH-20 during 2010–11 showed moderately resistant (MR) reaction against BND under field condition however, the varied absorbance was recorded as 0.97, 1.74, 1.01, 0.14 and 0.14, respectively in these genotypes. Whereas, during 2011–12, PWMH-34, PWMH-36 and PWMH-37 showed highly susceptible (HS) reaction under field condition. Absorbance of all the field evaluated genotypes during 2011–12 was ranged from 0.19–1.47. In glasshouse evaluation of selected 25 genotypes, C. colosynthis showed 40% transmission therefore it was found MR reaction while, the rest of genotypes showed HS reaction against WBNV. Moreover, five genotypes viz., PWMH-1, PWMH-2, PWMH-3, PWMH-12, and PWMH-20 showed MR reaction under field condition during 2010–11, but under glasshouse condition these genotypes showed HS reaction except the C. colosynthis. Value of absorbance at 15 DPI in glasshouse inoculated plants ranged from 0.12–0.90 with the percent transmission of 40–100% at 35 DPI. Therefore, C. colosynthis is the source of resistance against WBNV and it is being utilized in development of WBNV resistant varieties in the Indian conditions.