MID-PARENT HETEROSIS AND COMBINING ABILITY OF EUROPEAN CORN-BORER RESISTANCE IN MAIZE

Success in breeding maize resistant to the European corn borer has bee n limited, with the exception of leaf feeding resistance. The inherita nce of resistance to leaf, sheath-collar and ear damage in four maize germplasms and their six F-1 crosses was evaluated by diallel analysis . Plants in a completely randomized design were artificially infested at the whorl, anthesis or full silk stage of plant development and wer e evaluated in the field for insect damage. A damage index based on si ze, number and location of lesions was calculated for each stage. Stow ell's Evergreen (susceptible) had a mean damage index three to six tim es that of Maiz Amargo (resistant) at the whorl stage and the progeny plants were more resistant than the susceptible parent. Maiz Amargo an d its crosses had significantly lower mean indices than Stowell's Ever green for sheath-collar damage in Year 1 but not Year 2. Zapalote Chic o, Maiz Amargo and their cross were significantly less damaged than ot her genotypes at the full silk stage. Heterosis values indicated an in crease in resistance of crosses over the midparent average at all thre e stages of development. General combining ability (GCA) was highly si gnificant for all types of damage, but specific combining ability was significant only for leaf damage. Based on estimates of GCA, Maiz Amar go was the best source of resistance to leaf and sheath-collar damage and both Zapalote Chico and Maiz Amargo would be good parents for ear damage resistance. Results suggest that resistance at different plant development stages can be combined.