Analysis of morphological and growth rate variability of polyconidial and monoconidial cultures of <i>Bipolaris sorokiniana</i>

Abstract

Bipolaris sorokiniana is a phytopathogen of great importance on the wheat culture regions, causing diseases such as spot blotch, common root rot and back point of bthe grain. This fungus is widely distributed over the country and is responsible for a great loss on the production and commercialization of the grain. It has a high physiological and morphological variability what makes the development of control measures a difficult task. The aim of this work was to verify the influence of different culture media over this variability. For that, 21 isolates of B. sorokiniana were selected and from them polysporic and monosporic cultures were obtained. The morphological aspects such: coloration, edge, superficial texture aerial mycelium and color, and shape of the sectors; and the growth rate of the isolates were analyzed in four different media: potato dextrose agar (PDA), Sabouraud maltose, Sabouraud galactose and Sabouraud glucose. The monosporic cultures did not present significant difference in the growth rate among the different media. However, a small morphologic variation, as well as on the repetitions of the isolates in the same medium was obtained. By the other hand, polysporic cultures showed an high morphologic variability among the four media and also the morphologic variability was evident even in the repetitions of one isolate, in the same medium. Comparing monosporic and polysporic cultures, considering the growth rate, a significant difference (p< 0.05) was found in Sabouraud maltose and Sabouraud galactose media, for the polysporic cultures. However, no significant difference was observed in the monosporic cultures. Key words: Bipolaris sorokiniana , physiological variability, morphology, monoconidial and polyconidial culture