Rizoctoniose do feijoeiro : caracterização molecular do patógeno e controle biológico com leveduras

Abstract

The damping-off and stem rot caused by the soil pathogen Rhizoctonia solani, is considered one of the most important diseases of common bean (Phaseolus vulgaris) and cowpea (Vigna unguiculata), being one of the factors that contribute to the low productivity of these crops. This study aimed to characterize isolates of the causal agent of damping-off and stem rotof beans in the rural area of Pernambuco State, using microsatellite markers and phylogenetic analysis; and evaluate the use of yeasts in the control of the causal agent of damping-off and stem rot of beans. In bean growing areas of the southern region of Pernambuco, there were collections of plants with symptoms of damping-off and stem rot. Thirty-four fungal isolates were identified as Rhizoctonia. In the phylogenetic analysis, the sequences of ITS rDNA region of isolates were similar to at least three anastomosis groups (AG4 HG-I, AG3-PT and AG4 HG-III). In microsatellite analysis, five sets of primers (TC_AG3_1, TC01, TC06, TC11 and TC_AG3_09) amplified a total of 13 bands, showing genetic variation. Seventy R. solani were evaluated for aggressiveness, being the isolate CMM-3643 selected to the biological control trials. Seventy yeast isolates were obtained from apparently asymptomatic bean plants. From these, were chosen only isolates where the disease severity index was ≤ 25%. Experimental tests showed that the three yeast isolates (C6A, FVF10 (R1), FVC10) were selected as promising biocontrol agents of damping-off and stem rot of cowpea (cv. IPA-207), being efficient in controlling the disease caused by isolated CMM -3643. Increases in the levels of POX and CAT enzymes by treating the seeds with FVF10 yeast (R1), as well as, the absence of antibiosis mechanisms suggests that the biocontrol mechanism in question is the induction of disease resistance. In view of the results it is concluded that the AG4 HG-I is the primary anastomosis group causing damping-off and stem rot of beans in the São João municipality, Pernambuco State. In addition, this is the first report of damping-off and stem rot symptoms reduction in cowpea seedlings due to the antagonistic action of yeasts against R. solani.