Abstract
We examined the genetic variation in the callus performance of the Al-tolerant and Al-susceptible genotypes of sorghum (Sorghum bicolor L.) on Al-containing medium. Addition of Al to the medium with a low pH, low Ca and low phosphate resulted in a severe decrease in the percentage of callus formation (CF) in both Al-tolerant and Al-susceptible genotypes. However, the percentage of callus formation in the explants from Al-tolerant genotypes was higher than that from susceptible genotypes on Al-containing medium. The genotypic difference in the relative growth of calli on Al-containing medium and in the suppression of callus formation by Al was in agreement with that in the hematoxylin staining score. Al might have been considered as a limiting factor that affected the callus growth. There was a significant correlation (r = -0.664*) between the percent relative suppression of callus formation by Al and the percentage of callus formation on Al-containing medium. The callus growth in fresh weight and size on Al -containing medium relative to that on Al-free medium (relative growth on Al-containing medium) was greater in Al-tolerant genotypes than in the other genotypes. The relative growth of callus in fresh weight and size on Al-containing medium significantly correlated (r = -0.820** and r = -0.956**, respectively) with the percent relative suppression of callus formation by Al. The tissue culture is considered to be a useful tool for selecting Al-tolerant haploids at the callus stage.
