RELATIONSHIPS AMONG LATE LEAFSPOT, HEALTHY LEAF-AREA DURATION, CANOPY REFLECTANCE, AND POD YIELD OF PEANUT

Experiments were conducted to investigate the relationships among disease severity, canopy reflectance, healthy leaf area duration, and pod yield of peanut. For Florunner, a cultivar susceptible to late leafspot (caused by Cercosporidium personatum), pod yield in 1988 and 1989 decreased as the duration of healthy leaf area (HAD) decreased. Several levels of cumulative stress from disease (estimated by the HAD) were obtained by periodic sprays of four rates of the fungicide chlorothalonil. Canopy reflectance at 800 nm decreased as disease severity and defoliation increased during the season. Regression of reflectance against green leaf area gave coefficients of determination (R2) of 0.77 in 1988 and 0.95 in 1989 for Florunner and 0.87 in 1989 for Southern Runner. The pod yield of Florunner was reasonably predicted from HAD for all treatments except the untreated control. The prediction model was developed earlier by averaging the loss of pods that accompanied a delay in harvest of 78 crops of Florunner. The original model was then modified with a scaling factor for maturity of the crop at harvest. The yields predicted from HAD with the newly scaled model were within 11% of the actual yield of Florunner in 1988 and 1989. The yield predicted with the model for Southern Runner, a cultivar known to produce more foliage and to partition proportionately less photosynthate to the pods than Florunner, was overestimated by an average of 18%. Modification of the model parameters to account for the lower partitioning of photosynthate for Southern Runner brought the average predicted pod yields within 6% of the actual yields. The HAD-yield relationship may be used to estimate the relative, radiation-use efficiency of a peanut cultivar.