Response of Peanut Genotypes with Differential Levels of Leafspot Resistance to Fungicide Treatments

Abstract

Leafspot diseases, caused by Cercospora arachidicola S. Hori (early leafspot) and Cercosporidium personatum (Berk, and Curt.) Deighton (late leafspot), are worldwide production problems on peanut (Arachis hypogaea L.). The extensive use of fungicides to control these diseases on susceptible cultivars is costly to growers. Developing leafspot resistant cultivars is a primary objective in many breeding programs. ‘Southern Runner’, which was released in 1986, is the only commercially available peanut cultivar in the USA with significant leafspot resistance. Field studies were conducted in 1981 to 1983 and 1985 to 1987 on peanut breeding lines with varying levels of leafspot resistance to evaluate their disease reaction and agronomic response to three leafspot fungicide programs and to assess their potential as cultivars for use with fewer fungicide sprays. The cultivars Florunner (susceptible) and Southern Runner (moderately resistant) and three breeding lines were used in all 6 yr, with five additional lines unique to the 1981 to 1983 experiments and four additional lines unique to the 1985 to 1987 tests. All experiments were randomized‐complete block, split‐plot designs with genotypes as subplots and three fungicide spray programs as main plot treatments: (i) unsprayed, (ii) chlorothalonil (tetrachloroisophthalonitrile), 500 g L‐1 on 20‐d, and (iii) 14‐d spray schedules. Leafspot disease ratings were on a 1 to 10 scale, with 1 = no disease and 10 = dead plants, assessed prior to digging. Significant (P ≤ 0.01) genotypic differences for pod yield, percent total sound mature kernels, seed weights, and disease ratings were noted. Significant (P ≤ 0.01) differences were obtained for years, fungicide treatments, and most two‐ and three‐way interactions. Negative correlations were obtained between pod yields and disease ratings for unsprayed (r = ‐0.64) and 20‐d schedules (r = ‐0.46), but not for the 14‐d treatment. No differences in pod yield were obtained between the 14‐d (eight sprays) and the 20‐d (four sprays) fungicide treatments on the leafspot resistant genotypes. Results indicated that it is possible to develop commercially acceptable peanut cultivars with leafspot resistance that reduces the need for fungicide control of leaf‐spots.