Disease resistance and biomass stability of forage pearl millet hybrids with partial rust resistance

The expression of partial resistance to Puccinia substriata var. indica and its contribution to digestible biomass production in forage pearl miller h ybrids were evaluated in field experiments at Tifton, GA. Inbreds Tift 383, Tift 65, and nine inbreds with partial resistance selected from the cross Tift 383 x 'ICMP 501' were crossed to Tift 23DA(4). The parental inbreds an d hybrids were evaluated in natural epidemics in 1996 and 1997. Because of maturity differences among the lines, slope of the regression of legit rust severity on time (apparent infection rate) and area under the disease prog ress curve (AUDPC) calculated for a defined interval of plant growth (10 da ys before to 20 days after anthesis) and adjusted for initial rust severity at 10 days prior to anthesis were the most useful indicators of resistance . Inbred resistance was not a reliable predictor of hybrid resistance when evaluated by either variable. Hybrids were evaluated for biomass production in 1996 and 1997 in a split-plot design, with hybrids as main plots and no ntreated or chlorothalonil fungicide-treated as subplots. Differences exist ed among hybrids for AUDPC and for digestible dry matter yield (DDMY) and i ts components. Over all hybrids, the response between DDMY and final rust s everity was described by logarithmic regression. Two clusters of hybrids we re identified by cluster analysis of disease-related data from both experim ents. The cluster of susceptible hybrids tended to have a lower DDMY and we re less stable over year x treatment environments than the cluster of parti ally resistant hybrids. Lodging in nontreated plots in 1997 primarily occur red in susceptible hybrids. Although resistance was expressed in certain hy brids, greater levels of partial resistance are needed to provide adequate protection against DDMY losses.