Amplified Fragment Length Polymorphism Diversity in Cephalosporium maydis from Egypt.

ABSTRACT Cephalosporium maydis, the causal agent of late wilt of maize, was first described in Egypt in the 1960s, where it can cause yield losses of up to 40% in susceptible plantings. We characterized 866 isolates of C. maydis collected from 14 governates in Egypt, 7 in the Nile River Delta and 7 in southern (Middle and Upper) Egypt, with amplified fragment length polymorphism (AFLP) markers. The four AFLP primer-pair combinations generated 68 bands, 25 of which were polymorphic, resulting in 52 clonal haplotypes that clustered the 866 isolates into four phylogenetic lineages. Three lineages were found in both the Nile River Delta and southern Egypt. Lineage IV, the most diverse group (20 haplotypes), was recovered only from governates in the Nile River Delta. In some locations, one lineage dominated (up to 98% of the isolates recovered) and, from some fields, only a single haplotype was recovered. Under field conditions in Egypt, there is no evidence that C. maydis reproduces sexually. The nonuniform geographic distribution of the pathogen lineages within the country could be due to differences in climate or in the farming system, because host material differs in susceptibility and C. maydis lineages differ in pathogenicity.

Relative Competitiveness and Virulence of Four Clonal Lineages of Cephalosporium maydis from Egypt Toward Greenhouse-Grown Maize.

Four clonal lineages of Cephalosporium maydis, a soilborne vascular wilt pathogen that causes late wilt of maize, were differentiated previously with molecular markers. In Egypt, this fungus can cause significant losses in infected susceptible plants. In greenhouse tests of individual isolates we found that these lineages differ in their virulence toward a series of maize accessions commonly used in Egyptian maize breeding programs. We also determined the relative competitiveness of representatives of the four lineages when incorporated into the soil as a mixed inoculum. The lineage (IV) with greatest mean disease incidence (virulence), when tested alone, was the least competitive on susceptible maize accessions when coinoculated as a component of mixed inocula of all four lineages. In these coinoculation experiments, one of the less-virulent lineages (II) dominated (70% of infections) and appeared to be the most competitive. These results suggest that virulence and competitive ability are not the same in this host-pathogen system. These results also suggest that standard protocols that rely on mixed inocula for resistance screening need to be altered, and that the relative proportion of the different lineages of the pathogen recovered in a field may be influenced by the maize variety/hybrid planted.