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Estimates of Heterosis and Combining Ability for Resistance of Maize to Colletotrichum graminicola. S. M. Lim, Research Plant Pathologist, Federal Research, Science and Education Administration, U.S. Department of Agriculture, University of Illinois, Urbana, IL 61801; D. G. White, Assistant Professor, Department of Plant Pathology, University of Illinois, Urbana, IL 61801. Phytopathology 68:1336-1342. Accepted for publication 12 April 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1336.

Various heterosis constants for resistance in maize to leaf blight and stalk rot caused by Colletotrichum graminicola were estimated from 45 F1 diallel crosses and their ten parental inbreds. Leaf blight reactions, disease severity, and lesion lengths were evaluated on seedlings (five- to six-leaf stage) in the greenhouse and on adult plants in the field 2 wk after mid-silk. Stalk rot reactions, number of internodes discolored 75% or more, and total number of internodes discolored were evaluated in the field following artificial inoculation. Seedling blight reactions in the greenhouse were significantly correlated with leaf blight reactions of adult plants in the field, but leaf blight was not correlated with stalk rot. All constants, parental inbreds (Vi), overall heterosis (hij), the average heterosis (h*), the parent heterosis (hi), general (g.c.a.) and specific combining ability (s.c.a.), and mean squares (m.s.) were significant for all disease evaluations except h* effects for stalk rot reactions (number of internodes discolored 75% or more) and s.c.a. effects for lesion length from adult plants. Overall heterosis effects accounted for 29 to 43% of the disease severity of the entry sum of square (s.s.). Certain susceptible inbreds contributed more heterosis for resistance in single crosses than resistant inbreds. However, crosses between resistant inbreds were more resistant to C. graminicola for both leaf blight and stalk rot than were those involving intermediately resistant or susceptible inbreds. Of inbreds used in the study, Pa91 and T111 were the most resistant to leaf blight. The significant g.c.a. effects for resistance were usually found from resistant inbreds. Based on predominant additive gene effects and partial dominance for resistance, we believe that combinations of inbreds resistant to leaf blight with inbreds resistant to stalk rot may be used to produce hybrid corn resistant to both leaf blight and stalk rot.

Additional keywords: Zea mays L., anthracnose, disease resistance, heterotic effects, genetic constants, combining ability.