Date of Award

1984

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The inheritance of resistance to leaf disease of rice (Oryza sativa L.), caused by the fungus Entyloma oryzae H. & P. Sydow & Sydow, was studied in an undefined diallel set of crosses involving five rice lines previously rated for leaf smut resistance. The five lines consisted of two very resistant lines, two very susceptible lines, and one intermediate line. The diallel set of crosses consisted of the five parental lines considered to be non-random, 20 F(,1) hybrids obtained from the single crosses of the five lines in all combinations, and 20 F(,2) families derived from self-pollination of the F(,1) hybrid plants. The plants were evaluated on a 0-9 scale, with 0 and 9 indicating immune and very susceptible reactions, respectively. In 1983, a randomized block field experiment with four replications was conducted at the Rice Research Station, Crowley, Louisiana. Leaf smut infection occurred as a result of natural inoculum in the rice growing area in which the study was undertaken. The statistical analyses of the diallel cross were based on the model of Jinks and Hayman. Seven assumptions were tested and the assumptions of diploid segregation, homozygous parents, no reciprocal and no maternal effects were valid but the assumptions of no epistasis, no multiple allelism, and independent gene distributions were not strictly valid. Highly significant additive and dominance components using Hayman's analysis of variance were obtained in the F(,1) and F(,2) generations. Additive (D) and dominance (H(,1) and H(,2)) genetic variances, and the proportion of recessive versus dominant alleles in the parents (F) were quite similar from block to block, indicating that genotype-environmental interactions were rather small. The ratio of (H(,1)/D)(' 1/2) provided evidence for partial dominance in the parents while the ratio of H(,1)/4H(,2) suggested the occurrence of residual heterozygosity and complementary epistasis in the experiment. The data also showed that resistance to Entyloma oryzae was generally dominant over susceptibility and was controlled by a few major genes. Estimators of narrow-sense heritability were generally high and ranged from 66.50% to 79.28% indicating that the variation was mainly additive and suggesting selection for resistance should be quite effective.

Pages

166

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