Combining ability among early quality protein maize inbred lines under stress and non stress environments
The general combining ability (GCA) and specific combining ability (SCA) are the main criteria for rapid genetic assaying of test genotypes under the line by tester analysis. Information on GCA and SCA has been well documented both in temperate and tropical germplasm. However, little information is known on combining ability of early Quality Protein Maize (QPM) inbred lines under stress and non-stress conditions especially in the tropics. Therefore the objectives of this study were: i) To determine performance of early QPM inbred lines under stress and non-stress conditions ii) To determine performance of early QPM top cross and three way hybrids under stress and non-stress condition iii) Estimate the GCA and SCA of early QPM inbred lines under stress and non-stress conditions. A total of 50 early QPM inbred lines selected based on performance of the top cross hybrids were advanced to S4 and crossed to three testers (Susuma, ECA-QPOPE and CML144 x 159). A total of 150 early QPM hybrids plus six experimental checks were evaluated across drought and non drought environment. All experiments were planted in alpha lattice design. Three sites (Kiboko, Embu and Namulonge) were under well watered environments while one site (Kiboko) was under managed drought environment. Data was collected on grain yield and secondary traits. Individual and combined analyses of variance (ANOVA) were performed using proc GLM of SAS. All sites were significant for grain yield. The average grain yield across sites was 6.5 t/ha with a range of 4.7 t/ha to 8.8 tlha. The average grain yield under managed drought stress was 2.1 t/ha with a range of 0.3 tJha to 5.0 tlha. The best four hybrids under drought involved inbred lines with tester 3 (Susuma) and the best hybrid under drought (inbred line15 x tester 3) was also the best hybrid across non drought conditions. Mean grain yield across non drought conditions was 8.0 tlha with a range of 5.6 tlha to 10.7 tlha. Grain yield for checks under managed drought stress ranged from 0.7 tlha to 2.0 tlha whereas under non drought conditions the range was 7.1 tlha to 10.7 tlha. The average grain yield for inbred lines under drought was 1.7 tlha with a range of 0.0 tlha to 3.2 tlha. Under non drought condition the average grain yield was 3.9 tlha with a range of 1.8 tlha to 6.5 tlha. Among the 50 early QPM inbred lines used in this study, 24 inbred lines recorded positive GCA for grain yield under drought. Several hybrids under drought were identified based on per se performance of the inbred line, its GCA and performance in hybrid combination. The hybrids included genotype 11, 12, 29, 126 and 135. Inbred line 44 had the highest positive GCA for grain yield (1.09 tlha) under non drought conditions. This inbred line had a high grain yield with all the three testers under non drought condition. Among 50 early QPM inbred lines used in this study, 21 lines exhibited positive GCA for grain yield under non drought conditions. Across sites, inbred line 13 had the highest positive and significant GCA for grain yield (0.99 tlha) with positive GCA for EPP and negative GCA for AS!. Other inbred lines with positive and significant GCA for grain yield across sites include inbred line 15, 28, 38 and 44. Good specific combiners under non drought conditions include genotype 8, 12, 54, 71 and genotype 93. These hybrids recorded high significant SCA effects for grain yield under non drought conditions. Good specific combiners under drought stress include genotype 5, 11, 12, 15, 35, 52, 105, 109, 112 and genotype 121. Thus these genotypes are potential hybrids for advanced yield testing and consequent release. The best inbred lines may be used as a future breeding stock of drought tolerant early QPM hybrids.