Peanut Breeding for Leafspot Resistance in Wide and Narrow Intrarow Spacings¹

Sixteen peanut (Arachis hypogaea L.) genotypes were grown without the use of fungicides for two years in two planting arrangements, one an intrarow spacing typically used in commercial production (5 cm between plants) and the other typically used in breeding selection plots (30 cm between plants). At 10-day intervals throughout each growing season the proportion of necrotic leaf area caused by leafspots (Cercospora arachidicola Hori and Cercosporidium personatum (Berk. & Curt.) Deighton), leafspot disease rating (0-9), and stage of vegetative growth (v stage) were assessed. Leafspot disease ratings of genotypes spaced 30-cm apart were significantly correlated with the ratings of genotypes in 5-cm spacing. There was no interaction between genotypes and spacing. Percentage necrotic area in 30-cm and 5-cm plantings was significantly correlated. However, large experimental error and complex interactions among spacings, genotypes, and time of observation lessened the value of this method of disease assessment. While the correlation of v stage in the two spacings was highly significant, differences among genotypes were not consistent.