Effect of pH and sucrose concentration on conidium size and septation in four Bipolaris species

Abstract

Initial pH and sucrose concentration of the medium markedly affected sporulation and conidial characteristics in four Bipolaris species. Bipolaris sorokiniana and B. zeicola sporulated well at all pH levels; B. setariae and B. maydis produced relatively fewer conidia. Most isolates of B. sorokiniana sporulated well at all sucrose concentrations; sporulation by B. zeicola and B. maydis was less abundant, particularly at high sucrose levels. Only one of six isolates of B. setariae produced conidia at sucrose concentrations higher than 5 g/litre.In all four species conidium length and number of septa per conidium significantly decreased as the pH of the medium was increased, although some isolates of B. sorokiniana showed great variability. Conidium width was less markedly affected. Generally, in B. sorokiniana conidium length and number of septa decreased as the sucrose concentration was increased from 1 g/litre to 30 g/litre. In B. zeicola, conidia of maximum length and number of septa were produced on sucrose concentrations of 5 g/litre. Conidial characteristics of B. maydis were less markedly affected by increases in sucrose concentration.