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Host Resistance to Stewart’s Disease in Maize. M. H. Blanco, Formerly graduate assistant, now research plant pathologist, O’s Gold Seed Company, Farmer City, IL; M. S. Zuber(2), J. R. Wallin(3), D. V. Loonan(4), and G. F. Krause(5). (2)Professor of agronomy, University of Missouri, Columbia; (3)Research plant pathologist, SEA, USDA; (4)Research technician, SEA, USDA; (5)Statistician, Missouri Agricultural Experiment Station, Columbia 65211. Phytopathology 69:849-853. Accepted for publication 1 March 1979 . Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-849.

The effect of host genotype, cytoplasm, and rating date on development of Stewart’s wilt (Erwinia stewartii [E. F. Smith] Dye) of corn (Zea mays L.) was studied. The 15 possible single crosses among six inbred line parents in both normal and Texas male-sterile cytoplasm were grown in a split-plot design, with the split on cytoplasms. In a diallel analysis, inbred parents B37, 33-16, and Mo17 had significant negative general combining ability (gca) effects for each of three rating dates. The parents B14A and N28 had significant positive gca effects, with B14A conditioning susceptibility in a dominant manner. Reaction to Stewart’s disease was largely additive in this set of crosses, as the gca mean square was 20 times the magnitude of the specific combining ability (sca) mean square. Therefore, the conventional recurrent selection method should be effective in improving populations for resistance to Stewart’s wilt disease. The most resistant plants could be identified before anthesis when artificially inoculated at about the 12th leaf stage. Highly significant differences were found among the 15 genotypes, three rating dates, and two cytoplasms, the differences between cytoplasms being the least important. Disease response interactions were significant for genotypes × rating date, cytoplasm × rating date, gca × rating date, and sca × rating date. The genes conditioning lesion development were determined to be inherited qualitatively by the Castle-Wright formula. Diallel mating schemes using multiple disease ratings over time should be useful in studying gene action affecting disease development or general resistance.

Additional keywords: bacterial wilt.