Diversidade genética e patogênica de Rhizoctonia solani do feijoeiro no Agreste Meridional de Pernambuco

Abstract

Rhizoctonia solani causes diseases on a range of hosts and one of the most important diseases on common bean and cowpea, known in Brazil as "rizoctoniose”, “mela” or “murcha da teia micélica”. This study aimed to characterize the genetic and pathogenic diversity of R. solani isolates obtained from common bean and cowpea with “rizoctoniose” symptoms in the Agreste Meridional of Pernambuco. Isolates of R. solani were evaluated regarding anastomosis groups (inferred from ITS rDNA phylogeny), morphology and pathogenicity. The genetic diversity was evaluated through the use of sequences of the ITS region of the rDNA. Fifty-seven isolates of R. solani were obtained from common bean and cowpea production areas. Colonies of the fungus isolated were initialy white, becoming brown or beige with age. The production of microsclerotia was observed only after 15 days of incubation. The growth rate of colonies ranged from 1.7 to 3.6 cm.day־¹. In the phylogeny using ITS rDNA the majority of isolates from commom bean and cowpea grouped together in the AG4 HG-I and one of cowpea grouped in AG2-2 IIIB. All isolates where patogenic to cowpea IPA-207 cultivar, showing severity levels from 40 to 92.8%. Thus, in the Agreste Meridional of Pernambuco, the “rizoctoniose” of cowpea and common bean is caused mainly by Rhizoctonia solani AG4 HG-I