Diversity of Macrophomina phaseolina from cotton in Egypt: Analysis of pathogenicity, chlorate phenotypes, and molecular characterization

Abstract

Pathogenicity of 21 isolates of Macrophomina phaseolina was tested on three cotton cultivars under greenhouse conditions. Analysis of variance (ANOVA) showed that the main effects of both isolates (P= 0.000) and cultivars (P= 0.000) were very highly significant sources of variation in postemergence dampingoff and survival. Isolate x cultivar interaction was also a significant source of variation in postemergence damping-off (P= 0.03) and survival (P= 0.04). Statistically significant isolate, cultivar, and isolate x cultivar interaction suggest that physiologic specialization exists within M. phaseolina isolates pathogenic on cotton. It also implies that the resistance of the tested cultivars is a mixture of both vertical and horizontal resistance and there are significant differences among cultivars in both types of resistance. Cluster analysis of the isolates, based on their virulence patterns on different cultivars, differentiated the isolates reasonably well and grouped them into three pathotypes. The isolates were distinguished phenotypically by using a defined medium containing 120 mM potassium chlorate. Chlorate-resistant isolates (33.3%) grew densely on chlorate medium, while the remaining isolates (66.7%) were chlorate sensitive and showed either a restricted (23.8%) or feathery (42.9%) growth. No associations were observed between grouping the isolates based on their virulence patterns and their chlorate phenotypes. Random amplified polymorphic DNA (RAPD) analysis was used to evaluate the genetic diversity of the isolates. In this analysis, polymerase chain reaction was performed by using four random decamer primers. All the primers detected polymorphisms in all the tested isolates. Cluster analysis by the unweighted pairgroup method of arithmetic mean (UPGMA) placed the isolates in three distinct groups. Grouping the isolates based on cluster analysis of their virulence patterns did not match that based on cluster analysis of their RAPD profiles while, grouping the isolates based on cluster analysis of their RAPD profile exhibited clear correlation with their chlorate phenotypes.