Interações entre Fusarium solani f. sp. phaseoli e Rhizoctonia solani na severidade da podridão radicular do feijoeiro

Abstract

The present work aimed to evaluate the effect of inoculum densities of Fusarium solani f. sp. phaseoli (Fsp) and Rhizoctonia solani (Rs) and their interactions on the severity of root rot and on the dry mass of bean plants. Soil was infested by the addition of Rs or Fsp-colonized sorghum seeds, in the amounts of 0.00 g; 0.06 g; 0.12 g; 0.25 g; 0.50 g; and 1.00 g for Rs, and 0 g; 1g; 2 g; 4 g; 8 g; and 16 g for Fsp per pot (1.4 kg of soil). The densities used for the joint soil infestations with both pathogens were the same used in the separate pathogen infestations. A progressive rise in the severity of root rots was observed with the increase of inoculum density for both pathogens. Maximum disease severities for Rs were 67% and 22%, in separate or combined infections with Fsp, respectively. Maximum disease severities with Fusarium were 14% and 38%, in separate or combined infections with Rs, respectively. The results suggest that Rhizoctonia solani stimulated the expression of symptoms of Fusarium solani f. sp. phaseoli, while Fsp inhibited the expression of symptoms caused by Rs. Negative correlations between the inoculum density and bean dry weight were generally observed, except for the single infestation with Fsp.