Genetic analysis of sorghum tolerance to aluminium toxicity among Ugandan breeding lines

Aluminium (Al) toxicity is a major abiotic constraint that limits grain sorghum (Sorghum bicolor L. Moench) production on acid soils. It inhibits water and mineral uptake and ultimately, reduces plant vigour and yield. A preliminary study was done to determine the level of variation for tolerance to Al3+ toxicity and to identify new sources of Al3+ tolerance in the Uganda`s sorghum germplasm. Four day old germinated seedlings of 83 sorghum genotypes (including two tolerant checks O2 and C1 and one susceptible check L5) whose initial root length were measured, were subjected to 0 µM and 148 µM of Al3+ supplied as Al2 (SO4)3.16H2O in Hoagland's nutrient solution as described by Magnavacaet al (1978). The seedlings were raised in a growth chamber for five days, after which final root lengths were recorded. Net root growth in the aluminium augmented solution was used to classify the germplasm into phenotypic classes of tolerant, moderately tolerant or susceptible. The above classification was used as a criterion for choosing progenitors for developing segregating populations for studies of inheritance. There were significant differences between the genotypes, Al3+ concentration and a significant interaction The genotypes O2, C1 and UNGB 2672 exhibited the highest net root length and were classified as tolerant while L5, UNGB 2759, UNGB 2856 and UNGB 2762 exhibited the lowest net root length and were therefore, classified as susceptible. The above were then used to develop segregating population for inheritance studies. On the other hand, when the remaining genotypes were analyzed, a high significant difference among the genotypes (P≤0.001) and a high significant (P≤0.001) interaction between the treatment levels and genotypes and a significant difference (P≤0.05) in Al3+ level. The genotypes/crosses were also significantly different (P≤0.001) from each other in regards to haematoxylin staining. Significant but negative correlation between haematoxylin staining and net root length of test genotypes (r2 = -0.94) was discovered. Significant differences were observed for Al3+ level, genotypes and interaction all at (P≤0.001) when the F2 and parental lines were analyzed. The reduction of net root length at 148 µM to the control computed showed that genotypes with larger values were tolerant to Al3+ toxicity; while those with very low ratios were as well very sensitive to Al3+.