Description

Abstract: Late leaf spot (LLS) caused by Cercosporidium personatum (Berk. & Curt.) Deighton reduces leaf CO2 assimilation rate (Asat) and accelerates leaf defoliation, which together lead to major reductions in peanut (Arachis hypogaea L.) yield worldwide. This study was conducted to determine whether differences in photosynthetic response to LLS severity exist among peanut cultivars of differing resistance. Field experiments were conducted in 2008 and 2009 to study the effects of LLS on Asat of tagged leaf cohorts, and photosynthetic response of similar age leaves to LLS in peanut cultivars with more (York) and less (Carver) quantitative resistance. A nonlinear model, y = (1 ? x)? was used to analyze Asat data, where y is relative Asat, x is measured visual lesion area, and ? represents the relationship between virtual and visual lesion area. Progression of LLS severity on leaf cohorts was slower in York than in Carver. However, the reduction in Asat with leaf cohort age was similar across the cultivars. This paradox could be explained by a higher ? value in York (4.6) than in Carver (3.6), indicating a greater relative reduction in Asat beyond the necrotic lesion area in York. This greater reduction in Asat in York compared to Carver was most closely related to a reduction in maximum carboxylation velocity. Results indicated that future efforts to improve LLS resistance should include sustaining Asat in response to LLS infection along with slower disease progress.