Genetic characterization of Cercospora sorghi from cultivated and wild sorghum and its relationship to other Cercospora fungi

Genetic variability and population structure of Cercospora sorghi from wild and cultivated sorghum were investigated to gain insight into their potential impact on epidemics of gray leaf spot of sorghum in Africa. Population structure was examined using data derived from amplified fragment length polymorphism (AFLP) of C. sorghi by Nei's test for population differentiation, G(ST), and analysis of molecular variation (AMOVA). Two ecological populations of C. sorghi in Uganda were devoid of population structure (G(ST) = 0.03, phiF(ST) = 0.01, P = 0.291). AMOVA revealed that genetic variability was due mainly to variations within (99%) rather than between (0.35%) populations, and Nei's genetic distance between the two populations was 0.014. Phenetic analysis based on AFLP data and polymerase chain reaction-restriction fragment length polymorphism analyses of the internal transcribed spacer regions of rDNA and mitochondrial small subunit rDNA separated Cercospora cereal pathogens from dicot pathogens but did not differentiate among C. sorghi isolates from wild and cultivated sorghum. Our results indicate that Ugandan populations of C. sorghi compose one epidemiological unit and suggest that wild sorghum, while not affecting genetic variability of the pathogen population, provides an alternative host for generating additional inoculum.