COMPONENTS OF RESISTANCE TO EARLY LEAF-SPOT IN PEANUT - GENETIC-VARIABILITY AND HERITABILITY

Early leaf spot (ELS) of peanut (Arachis hypogaea L.), caused by Cerco spora arachidicola S. Hori., is one of the most important diseases aff ecting peanuts worldwide. Host resistance would provide economical con trol. The nature and inheritance of resistance, essential to the devel opment of resistant cultivars, are poorly understood. Components of ra te-reducing resistance to ELS were evaluated in the field at Gwebi Var iety Testing Center, Harare, Zimbabwe, over four seasons, 1990/91 to 1 993/94, and for the 1995 and 1996 seasons in Gainesville, FL. Genotype s used were the parents and F-1, F-2, and F-3 progeny of full-diallel crosses involving parents 97/8/4, 148/7/25 (resistant), 'Flamingo' (in termediate), and 'Southern Runner' (susceptible). The components of re sistance evaluated were latent period (LP), defined as days from inocu lation to the first lesion sporulating; lesion diameter (LD); amount o f sporulation (SP); and maximum percent sporulating lesions (MSP) 20-2 5 days after inoculation. Significant differences (p less than or equa l to 0.05) were noted for all components in four or more tests. There were also significant genotype x environment interactions (P less than or equal to 0.05) for LP, LD, and MSP. Testing in multiple environmen ts is essential when breeding for resistance to ELS. Narrow-sense heri tability estimates ranged from 0.00 - 1.27 across components. Selectio n of sing le plants from crosses should be effective. Reciprocal diffe rences among some crosses for LP suggest the presence of a cytoplasmic factor in the inheritance of resistance to ELS.