Author : P.K. Dewi Hayati

Summary : Studies were conducted to screen and select maize inbred lines for tolerant to aluminum (AI) toxicity on acidic soil based on three different methods i.e. screening in nutrient solution, screening by hematoxylin staining and screening when grown in potted soils, identify the selected inbred lines for tolerance to acid soil, to determine their genetic diversity based on agronomic performance and SSR markers, and to evaluate their combining abilities in all possible crosses. Performance and heterosis of the single cross hybrids were evaluated on acidic and limed soil conditions at two different locations.. Genetic distances revealed by the SSR markets were used to predict hybrid performance. Low AI concentration in low ionic strength solution have severely inhibited maize root elongation. Concentration of 20 µM Al was found adequate to be used in distinguishing between Al-tolerant and Al-sensitive genotypes. In screening by hematoxylin staining, Al concentration between 5 and 30 µM were used in distinguishing roots Al-tolerant and Al-sensitive genotypes. Roots from the Al-tolerant genotypes were not affected by Al and hematoxylin. In potted soil experiments, two soil conditions (limed and unlimed) were applied screen genotypes for tolerance to acid soil. Results showed that some genotypes performed better on moderately acidic soils than they did on limed soils. Form theses screening experiments, inbred line IPB-12 consistently found to be Al tolerant. Results form evaluation on acidic and limed soils in the field showed that inbred lines IPB-12 and Sm-7-11 were identified as possessing moderate tolerance to acid soil and having potential to be high yielding in both soil conditions. SSR markers were found to be more successful in assessing genetic diversity among the inbred lines than did agronomic performance. However, genetic distances revealed by the SSR markers were not able to predict hybrid performance. From results of the hybrid evaluations, hybrids H29 and H24 which had positive and high SCA effects for tolerance to acid soils were found to have consistently shown high tolerance to acid soils at both locations. In addition, these hybrids showed high mid-and better parent heterosis. Five hybrids, namely H29, H24, H9, H23 and H4 consistently revealed high yields on acidic soils at both locations, giving average grain yield of 2875, 2871, 2668 and 2587 kg ha ha¯¹, respectively. Yields of these potential hybrids were higher than Sukmaraga planted as acid soil-tolerant check variety (2563 kg ha¯¹) and hybrid Putra J-58 (2179 kg ha¯¹). From the same evaluations, hybrids H21, H36, H25, H10 and H29 consistently revealed high yields on limed soils, giving average grain yields of 6164, 6002, 5665, 5404 and 5364 kg ha¯¹, respectively. Their yields were higher than Sukmaraga and Putra J-58 (5088 and 5310 kg ha¯¹), respectively. Only hybrid H29 gave high grain yield in each soil condition at each location. When data from both soil conditions and locations were combined, hybrid H29 gave higher yield (4117 kg ha¯¹) compared to Sukmaraga and Putra J-58 (3744 and 3826 kg ha¯¹, respectively). In general, the hybirds exhibited high and significant heterosis for tolerance to acid soils, grain yield and other important traits measured. Heterosis estimates for yield and yield components on acidic soils were higher than those on limed soils. Grain yield was highly correlated with yield components, agronomic, flowering and maturity traits on both acidic and limed soils. However, the relationships were stronger on acidic than those on limed soils. Meanwhile, tolerance to acid soils was correlated with grain yield and the yield components only in the acidic soil conditions. The estimates of broad-and narrow-sense heritability were generally lower on acidic than those on limed soil conditions. The narrow-sense heretability estimates were consistently lower than the broad-sense heretability estimates. Ear length, number of kernel rows per ear and number of kernels per row showed higher broad-and narrow-sense heritability estimates as compared to other traits measured. Analysis on combining ability among the nine miaze inbred lines showed the presence of both additive and non-addtive gene actions for tolerance to acid soils, grain yield and othet important traits measured on each soil condition. However, the additive gene effects were more important than non-additive geen effects since the mean squares for general combining ability anlysis (GCA) were found grater than the mean squares for specific combining analysis (SCA). When data from both locations were combined, proportions of additive variances for grain yield on acidic soils was lower (29.4%) than those on limed soil conditions (54.2%). higher ratio of the SCA varaiance to the GCA variance in the acidic soil conditions indicated that non-additive geen actions were more important in acidic than those in limed conditions. Meanwhile, the Wr-Vr analysis in general indicates the preponderance of overdominance geen actions in the control of tolerance to acid soils, grain yield and other important traits measured on both soil conditions. The influence of overdominance gene actions in the genetic control of grain yield and yield components was greater on limed soils than it was on acidic soils.