Basal root rot of mature plants of tomato caused by Pythium aphanidermatum (Oomycota).

Abstract

Basal root rot of mature plants of tomato caused by Pythium aphanidermatum (Oomycota). In roots of adult tomato plants a wet and brown lesion, extending 2-4 cm above the soil was observed. Diseased plants withered and died. The objective of this paper was to isolate and to identify the causal organism of these symptoms. General and selective culture media were used. After 24 hours colonies with white cottony mycelium were developed. The morphology of the colony and the production, morphology and size of reproductive structures were evaluated. The rDNA extraction was made from mycelium of pure cultures 7-10 days old grown in agarized media. The ITS region was amplified using ITS4 and ITS5 primers, sequenced and compared in gene bank - NCBI BLAST server to verify their sequence similarity to the type or holotype available. Coenocytic mycelium, spherical-globular sporangium and aplerotic oospores, characteristic of the genus Pythium were observed in microscopic slides. Pathogenicity tests were conducted with positive results; a microorganism identical to the original was re-isolated. The characterization achieved by traditional techniques, molecular studies and the results of the pathogenicity tests support the conclusion that Pythium aphanidermatum is the causal agent of basal rot on mature plants of tomato