AnÃlise morfolÃgica e genÃtica de isolados de Rhizoctonia solani e estudos epidemiolÃgicos de grupos de anastomose (AGs) em algodÃo / Morphological and genetic analysis of Rhizoctonia solani isolates and epidemiological studies of anastomosis groups (AGs) in cotton

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The knowledge anastomosis groups (AG) of Rhizoctonia solani populations, which cause cotton damping-off and sudden death in Brazil, the pathogen morphological features and disease epidemiology foster the establishment of more efficient disease management strategies in the field. Initially, 51 isolates were obtained from cotton seedlings originated from crop fields in Minas Gerais (MG), Bahia (BA), GoiÃs (GO), Mato Grosso (MT) and Mato Grosso do Sul (MS). They were studied for their morphological and molecular features to determine the assigned AGs and pathogenicity. For morphology, 36 isolates were identified as R. solani AG - 4 and two as R. solani AG - 7. The remaining 13 strains could not be grouped to any AG. In the molecular analysis, the 36 AG4-match and 10 of the AG unmatched were all grouped as AG4. Both isolates previously assigned to AG â 7- and one AG-unmatch was grouped as AG-7. Two isolates were characterized as binucleate Rhizoctonia spp. and one of them assigned to AG â P and the other to AG â A. In regard to pathogenicity, 92% of isolates were pathogenic to cotton, 51% of which (18MG; 3BA; 1MS; 2GO) showed high aggressiveness, averaging 3.4 to 3.9 severity. Based on the obtained results 18 isolates were tested at temperatures of 15, 18, 21, 24, 27 and 30 ÂC for mycelial growth, sclerotium production and pathogenicity were evaluated. There was a significant interaction between isolates and temperatures for all three studied variables. For MGR, a better fit to the squared model at 21, 24 and 27 ÂC was observed. But also a better fit to the linear model and maximum MGR at 30 ÂC. The highest sclerotium count was observed at temperatures of 15 and 18 ÂC, for all isolates, except for a MS isolate for which the optimum temperature was 27 ÂC. Fourteen isolates (6 from MG; 2 from BA; 2 from GO; 3 from MT and 1 from MS) presented higher severity between 24 and 27 ÂC, better fitting to the squared model. However, three isolates (2 from MG; 1 from MT) were significantly similar for the evaluated temperatures and for only one isolate (BA 2 â I01), a better fit to the linear model was observed with consequent higher severity at 30 ÂC.

ASSUNTO(S)

biologia molecular epidemiology tombamento rhizoctonia solani algodÃo dampinf-off cotton rhizoctonia solani fitopatologia epidemiologia biology

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