Temporal and spatial development, relative fitness and dynamics of strains of Colletotrichum sublineolum on grain sorghum

Field and greenhouse experiments were conducted using three sorghum cultivars and three strains of Colletotrichum sublineolum to quantify disease development of sorghum anthracnose and to determine the relationship between infection components and the dynamics of population structure of the strains in inoculated plots.; The results demonstrated that sorghum anthracnose developed slowly before anthesis and increased rapidly 50 to 80 days after inoculation (DAI). The resistant cultivar, Cargill 888Y, had significantly lower values of standard area under the disease progress curve (sAUDPC, lower upper asymptote, and delayed epidemic onset estimated from a nonlinear logistic model than BTx623 and Pioneer 8313. The disease gradients were described well by a negative exponential model. There were significant differences in intercepts but not in slopes of the disease gradients between the resistant and susceptible cultivars. The significantly lower slopes and higher half-distance values were estimated at 78 DAI than at 57 DAI for all cultivars.; A total of 1252 isolates of the fungus were recovered from field plots inoculated with an equal ratio of three strains and characterized using DNA restriction fragment length polymorphism markers. Results showed that one strain, TX-430BB, dominated populations of C. sublineolum from all three cultivars. However, there was a lower rate of selection for the most aggressive strain, TX-430BB, and higher levels of population diversity on the resistant cultivar than on susceptible cultivars. The population structure from non-inoculated rows was less diverse than from inoculated rows on the resistant cultivar.; Results of studies on infection components showed that strain TX-430BB had significantly higher values of sAUDPC, lesion expansion rate, lesion size, infection efficiency, sporulation and a shorter latent period than strains 54 and SS-1 on two susceptible cultivars, but not on the resistant cultivar. The order of relative fitness values on cultivars BTx623 and Pioneer 8313 was TX-430BB > 54 > SS-1, but no differences between strains TX-430BB and 54 were observed on Cargill 888Y. These results may explain the predominance of TX-430BB in populations from these two susceptible cultivars in plots inoculated with three strains of C. sublineolum.