Heritability and Resource AIlocation of AIuminum Tolerance Derived from Soybean PI 416937

Aluminum toxicity restricts soybean [Glycine max (L.) Merr.] yield in many growing areas. When correction of toxicity by management is impractical, an economically sound alternative is to develop Al tolerant cultivars. Heritability (h 2 ) estimates for Al tolerance in hydroponics would aid in the efficient design of selection programs for cultivar development. Our objectives were to determine the h 2 of Al tolerance in a F 4 -derived population using tap root extension in hydroponics culture as the indicator of tolerance. The 120 random F 4 -derived lines of sensitive 'Young' x tolerant PI 416937 were evaluated in the absence (NOAL) and presence (HIAL) of Al (2 μM Al 3+ activity) by means of a split-plot design. Aluminum stress increased seedling tap root extension 3% in PI 416937 and decreased extension in Young 53%. Mean progeny performance decreased 31%. Analysis of variance revealed significant (P < 0.05) progeny and progeny x Al interaction effects, indicating heritable genetic variation for Al tolerance. The h 2 under HIAL was moderate (0.57) on a single-replication basis and high (0.87) based upon five replicates, indicating the relative ease by which Al tolerance may be improved. Tolerance expressed as percent of control (PC) had a similar h 2 . Approximately 6% of the F 4 -derived progeny in this study were numerically similar to the parents for Al response under HIAL, suggesting that three to five genes may control Al tolerance and that a population size of 150 random inbred lines may be needed to assure full recovery of Al tolerance in the progeny of future breeding populations. Expected gain and risk avoidance analysis suggested that two or three replications are sufficient for initial screening of single seed descent (SSD) populations derived from the PI 416937 and that employment of this PI as a control enhances the ability of the breeder to discard inferior types during screening. Practical advice is presented to assist plant breeders in the efficient improvement of Al tolerance in soybean.