Reaction of common bean cultivars to root rot caused by Rhizoctonia solani and Fusarium solani f. sp. phaseoli

Rhizoctonia solani Kuhn is a necrotrophic fungus and soil inhabitant that attacks great number of vegetable species. In bean plants, R. solani can induce different symptoms including toppling, root and colon plant rottenness. Fusarium solani (Mart) Sacc. f. sp. phaseoli (Burcholder) occurs in practically all bean producing areas in Brazil and can cause root rots and death to bean plants. This study evaluated the reaction of commercial common bean cultivars growing in R. solani or F. solani f. sp. phaseoli infested soil, under green house conditions. The experimental design was entirely randomized, with 24 treatments and four replications. A Oxisol was infested with triturated sorghum grains that were previously colonized by R. solani (1.0 g/1.4 L of soil) or F. solani f. sp phaseoli (8.0 g/1.4 L of soil). The disease evaluations were accomplished 21 days after planting. All plants were carefully removed, their root systems were washed in running water and the disease severity was evaluated according to Abawi & Pastor-Corrales (1990) scale for disease severity. The cultivar behavior ranged according to the inoculated pathogen, all cultivars were susceptible with different degrees of susceptibility. Among evaluated common bean cultivars Perola was less susceptible to R. solani, and Radiante was less susceptible to F. solani f. sp. phaseoli.Original Abstract: Rhizoctonia solani Kuhn e um fungo necrotrofico, habitante do solo, que ataca grande numero de especies vegetais. Em feijoeiro, R. solani pode induzir sintomas como tombamento, podridoes de raizes e de colo da planta. Fusarium solani (Mart) Sacc. f. sp. phaseoli (Burcholder) ocorre em praticamente todas as regioes produtoras de feijao no Brasil e pode causar podridao radicular e morte das plantas. Neste trabalho, avaliou-se a reacao de cultivares de feijoeiro comum as podridoes radiculares causadas por R. solani e F. solani f. sp. phaseoli, em solo artificialmente infestado, em condicoes de casa de vegetacao. O delineamento experimental foi inteiramente casualizado, com 24 tratamentos e quatro repeticoes. Utilizouse solo Latassolo vermelho-escuro, infestado com 1,0 g de graos de sorgo triturado e previamente infestado com R. solani para cada 1,4 kg de solo e para F. solani f. sp. phaseoli utilizaram-se oito gramas para cada 1,4 kg de solo. A avaliacao da doenca foi realizada 21 dias apos o plantio, em plantas cujo sistema radicular foi cuidadosamente retirado e lavado em agua corrente. A severidade da do