Abstract
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 S1 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 F1, F2, BC1 (F1 × P1) and BC2 (F1 × P2), 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.
Highlights
Watermelon (Citrullus lanatus [Thunb.] Matsum & Nakai) stands out as one of the most produced vegetable crops in Brazil with total 2.28 million of tonnes produced in 2019 (FAO 2019)
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)
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
Summary
Watermelon (Citrullus lanatus [Thunb.] Matsum & Nakai) stands out as one of the most produced vegetable crops in Brazil with total 2.28 million of tonnes produced in 2019 (FAO 2019). Northeast region is the main producing regions with 40.83 thousand hectares and 775.32 thousand ton (IBGE 2019). Diseases caused by fungi soil inhabitants, such as dampingoff, caused by the fungus Rhizoctonia solani, are one of the factors that may limit watermelon production. Rhizoctonia solani has a great saprophytic capacity, can survive in the soil for many years using resistance structures, the sclerotia. It is a fungus that has a wide host range and can reach up to 190 species (Lakshman et al 2008). In Brazil, there are no registered products for chemical control of this disease in watermelon (MAPA 2021). The most efficient method is breeding for resistant cultivars by introducing genes of resistance in commercial cultivars
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