Temporal and Spatial Development of Sorghum Anthracnose in Arkansas

Development of sorghum anthracnose in time and space on susceptible ('BTx623' and 'Pioneer 8313') and resistant ('Cargill 888Y') sorghum (Sorghum bicolor) cultivars was investigated in field plots inoculated with a mixture of three strains (T430-SW, Ar54-SW, and ArSS-1SW) of Colletotrichum sublineolum in 2001 and 2002. After slow development during early growth stages, sorghum anthracnose developed rapidly after flowering. The logistic model provided a good statistical fit for disease progress curves for sorghum anthracnose in Arkansas. Compared to susceptible cultivars, the resistant cultivar had significantly lower values for the standard area under the disease progress curve, a lower upper asymptote, and delayed epidemic onset. However, there were no significant differences in infection rate and the time of the inflection points, the times at which the disease proportion equaled values of one-half of upper asymptotes, among the three cultivars. The negative exponential model more closely described disease gradients of sorghum anthracnose than the inverse power law model. There were significant differences in intercepts but not in slopes and half-distance between the resistant and susceptible cultivars. The slopes of disease gradients were significantly lower at 78 days after inoculation (DAI) than at 57 DAI on the three cultivars. The results could provide epidemiological components of sorghum anthracnose to help evaluate sorghum cultivars and breeding lines under field conditions.