COMBINING ABILITY AND GENE ACTION IN MAIZE (Zea mays L.)

Name of the Author : RAJITHA ATHOTA Title of the thesis : COMBINING ABILITY AND GENE ACTION IN MAIZE (Zea mays L.) Degree to which it is submitted : Master of Science in Agriculture Faculty : Agriculture Department : GENETICS AND PLANT BREEDING Chairperson : Dr. D. RATNA BABU University : Acharya N.G. Ranga Agricultural University Year of Submission : 2013 The present investigation was carried out during kharif 2012 at Agricultural College Farm, Bapatla to study the variability, heritability, expected genetic advance, combining ability, heterosis, character association and path coefficient analysis involving eight parents (five lines  three testers), 15 F1s along with check in maize for characters viz., days to 50% tasseling, days to 50% silking, days to maturity, plant height (cm), cob length (cm), kernel rows per cob, 100-seed weight (g), grain protein content (%) and grain yield per plant (g). Analysis of variance revealed significant differences among the genotypes for all the characters studied, indicating a high degree of variability in the material. The estimates of heritability and genetic advance as per cent of mean were high for the characters viz., 100-seed weight, grain yield per plant, cob length and plant height. High heritability coupled with moderate genetic advance as per cent of mean was observed for grain protein content and kernel rows per cob. High heritability coupled with low genetic advance as per cent of mean was observed for days to 50% tasseling and days to 50% silking. While low heritability coupled with low genetic advance as per cent of mean was observed for days to maturity. The analysis of variance for combining ability revealed that lines, crosses and Line x Tester effects had significant amount of variability with in each of them for majority of the traits studied. The per cent contribution towards the total variance was maximum due to the interaction of lines and testers for the traits, grain yield per plant, 100-seed weight, days to 50% silking, grain protein content, days to 50% tasseling and days to maturity while contribution of lines alone was maximum towards the total variance for cob length, kernel rows per cob and plant height. Out of the five lines tested in the present investigation, BM-421 and BM-256 recorded significant general combining ability effects in desirable direction for four (days to 50% tasseling, plant height, cob length and grain protein content) and three (days to 50% silking, kernel rows per cob and grain yield per plant) characters, respectively. While the tester, BM-143 recorded significant general combining effect for grain protein content. None of the 15 Line x Tester combinations recorded significant sca effect for grain yield per plant. The cross BM-77 x BM-85 recorded significant sca effect for plant height and grain protein content. While the crosses BM-3 x RNBL-4351 and BM-421 x BM-85 showed for 100-seed weight. The gca effects of parents and sca effects of their hybrid combinations indicated that the crosses with high sca effects have resulted due to high x low, low x low and high x high gca combinations. Therefore, one can afford to include some low general combiners also along with good general combiners in hybridization programmes. Further, heterosis studies in general revealed that all the Line x Tester combinations registered significant positive heterosis over both mid and better parents for grain yield per plant. Out of the fifteen cross combinations, BM-256 x BM-85, BM256 x BM-143, BM-3 x RNBL-4351, BM-421 x BM-85 recorded highest significant relative heterosis and heterobeltiosis for grain yield. Though the per se performance of the parents are relatively low, the above combinations are heterotic indicating better nicking ability of the lines and testers involved. Majority of lines and testers which yielded heterotic hybrids registered good general combining abilities as well. With this it is evident that lines with good gca though having less per se may also yield heterotic combinations. This shows the importance of studying the combining ability effects of different lines to be used either in heterosis breeding or in combination and transgressive breeding. The estimates of sca and gca variance also revealed the predominance of nonadditive gene action in the inheritance of days to 50% tasseling, days to 50% silking, 100-seed weight, grain protein content and grain yield per plant while both additive and non-additive gene actions were predominant for days to maturity and kernel rows per cob whereas additive gene action was predominant for cob length. These gene actions were further confirmed by the ratios of gca variance to total genetic variance and the estimates of narrow sense heritability. Genotypic correlations in general are higher than phenotypic correlations indicating that the apparent associations are largely due to genetic reasons. The traits cob length, 100-seed weight, kernel rows per cob, plant height and days to 50% tasseling were found to possess significant association in desirable direction with grain yield per plant at both genotypic and phenotypic levels. While path analysis studies revealed that cob length, 100-seed weight and kernel rows per cob showed true relationship by establishing significant positive association and high positive direct effect on grain yield per plant. From this it can be inferred that simultaneous improvement in grain yield per plant is possible through manifestation of cob length, 100-seed weight and kernel rows per cob.