Genetic analysis of tolerance to aluminum toxicity in maize (zea mays).

Aluminum (Al) toxicity causes high yield losses and is directly linked to acidic soils. Application of lime can ameliorate this problem, but it is costly and not feasible for small scale farmers as they need to purchase both seed and lime. Developing maize varieties that are tolerant to Al toxicity is cheaper and feasible for small scale farmers. The purpose of this research was to i) identify maize genotypes with tolerance to Aluminum toxicity, ii) evaluate the general and specific combining abilities for the inbred lines and crosses respectively, iii) investigate the type of gene action conditioning tolerance to aluminum toxicity in tropical maize, and iv) determine if shoot length can be used as an indirect selection criterion for Al tolerance. Fourteen maize inbred lines (CZL 083, L151, L552, CZL0814, CML312, L12, L3233, CML511, L917, L2, CML538, L5522, CML 457, and CZL04007) were evaluated in hydroponic conditions containing different concentrations of Al (0, 5, 10, 15 and 20mg/ L) in a 14 x 5 factorial completely randomized design with 3 replications at the University of Zambia, plant physiology laboratory. Five parameters were measured: root length, shoot length, number of root hairs, root and shoot biomass on eleventh day after seed placement. Highly significant differences (P=0.001) were noted for both root and shoot lengths. The results showed that inbred line CML 538 was highly tolerant while inbred line L151 was the most susceptible with mean lengths of 15.44 cm and 6.11 cm respectively. To address objective ii, eleven inbred lines were selected and mated in an 8 male (4 moderately tolerant and 4 susceptible) x 3 female (resistant) North Carolina Design II. Results revealed that GCA effects due to both males and females were highly significantly (P= 0.001) different from zero for root biomass. The shoot length GCA effects (8.75 and 12.81) due to both male and female respectively were significant (P=0.01). Similarly, the GCA effects due to females and males for root length were significant P= 0.01 and P=0.05 respectively. The SCA effects for the shoot length and root biomass were significant (P= 0.02). Both additive and non additive gene action were identified to be important for the root length as indicated by a Baker’s ratio of 0.49. The association of root length to shoot length was significant
(correlation [r] = 0.72)