Effects of Leafspot on Leaf and Canopy Photosynthesis in Two Peanut Cultivars of Differing Resistance.

Crop protection strategies focused on minimizing quantitative crop losses rather than disease outbreaks offer a promising way to reduce fungicide use, and thus the overall cost of peanut (Arachis hypogaea L.) production. However, this requires improved understanding of relations among disease epidemics, plant physiological processes and peanut yield. Therefore, we conducted a replicated field experiment in Citra, Florida, where leafspot-susceptible (Carver) and leafspot-resistant (York) cultivars were grown under fungicide-treated and untreated conditions. Newly-formed leaves were tagged at several dates during the growing season, on which leaf photosynthetic parameters and percent leafspot disease were assessed in situ at routine intervals until leaflet abscission to quantify the degree of photosynthetic reduction caused by leafspot and determine the mechanistic basis for reduced photosynthesis. In addition, frequent measures of crop canopy assimilation were made to quantify effects of reduced leaf photosynthesis and/or increased leaflet senescence on canopy carbon exchange. Reductions in leaf photosynthesis were greater than the actual visible lesion area. This was a relatively unimportant factor at the canopy level for the susceptible cultivar as rapid and large losses of leaf area were the primary reason for reduced canopy photosynthesis. In the resistant cultivar, reduced leaf photosynthetic rates played are greater role in reductions of canopy photosynthesis. These findings possess implications for disease management on peanut cultivars differing in leafspot resistance.