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Disease Progression and Leaf Area Dynamics of Four Peanut Genotypes Differing in Resistance to Late Leafspot

Agronomy Dep., Iowa State Univ., Ames, IA 50011
Agronomy Dep., Univ. of Florida, Gainesville, FL 32611
North Florida Agric. Res. and Education Ctr., Quincy, FL 32351
Agric. Res. and Education Ctr., Rt. 3, Box 376, Marianna, FL 32446

^* Corresponding author.

Leafspot epidemics caused by Cercospora arachidicola Hori (CA) and Cercosporidium personatum (Berk. & Curt.) Deighton (CP) cur every year on peanut (Arachis hypogaea L.) in the southeastern USA and can reduce yields even in fungicide-treated fields. In this study, leafspot epidemic rates and leaf area dynamics were compared for the widely grown but susceptible cultivar Florunner and three genotypes (Southern Runner, F81206, and MA72x94-12) having partial resistance to CP. Field studies were conducted at Marianna, FL in 1983 and at Gainesville, FL in 1985. Percent necrotic area in three leaf canopy layers (estimated using modified Horsfall-Barratt diagrams), defoliation of the main stem (determined by counting missing leaflets), and leaf area index (LAI) were recorded at 7 10-d intervals. In plots receiving no fungicide, rates of disease progress were one-half to two-thirds as great and areas under disease progress curves were 10 to 30% as large for the resistant genotypes as for Florunner. All genotypes lost similar amounts of LAI in response to disease, but defoliation was more complete for Florunner than for the other genotypes. Maintenance of higher LAI by these resistant genotypes was associated with sustained leaf production until maturity. The combination of lower epidemic rates with continned leaf growth (compensating for diseased leaves) appears reduce the adverse effects of leafspot on assimilation and yield capability of these resistant lines. Nevertheless, leaf replacement is probably not the optimum mechanism for minimizing effects of leafspot diseases, because leaf growth requires energy that could otherwise be available for pod growth.

Received for publication May 15, 1989.