Inheritance of resistance to damping-off (Rhizoctonia solani) in watermelon

: This study aimed to find sources of resistance to damping-off and to determine the inheritance of resistance in watermelon. Firstly, 72 watermelon accessions were inoculated with CMM 1053 isolate of Rhizoctonia solani . Only two accessions (BGH 29 and BGH 76) were considered moderately resistant to the disease. The inoculated plants without symptoms from accession BGH-29 identified as resistant were self-fertilized and the inbred line S 1 was used for the crosses. The reaction to R. solani after inoculation of the segregating populations of the cross and backcrosses between susceptible cultivar Crimson Sweet and the inbred line BGH-29 was evaluated. In other experiment eight S1 lines of watermelon were inoculated with six different isolates of R. solani and the reaction was evaluated by partial diallel analysis using the Griffing’s method IV to obtain estimates of general resistance ability (GRA), general aggressiveness ability (GAA), and specific interaction ability (SIA). According to ratings of the susceptible and resistant parents, generations F 1 , F 2 , BC 1 (F 1 × P 1 ) and BC 2 (F 1 × P 2 ), resistance to damping-off was conferred by at least nine genes with additive effect and low heritability which indicates polygenic inheritance. The results of the diallel analysis corroborate with the analysis of segregating population, indicating inheritance of resistance was horizontal, since 46.1% of the total sum of squares of the variation observed in the crosses was due to GRA, while the SIA corresponded to only 20.39% of variation. This is the first report about inheritance of resistance to damping-off caused by R. solani in watermelon.