HERITABILITY AND RESOURCE-ALLOCATION OF ALUMINUM TOLERANCE DERIVED FROM SOYBEAN PI-416937

Aluminum toxicity restricts soybean [Glycine mar(L.) Merr.] yield in m any growing areas. When correction of toxicity by management is imprac tical, an economically sound alternative is to develop Al tolerant cul tivars. Heritability (BZ) estimates for Al tolerance in hydroponics wo uld aid in the efficient design of selection programs for cultivar dev elopment. Our objectives were to determine the h(2) of Al tolerance in a F-4-derived population using tap root extension in hydroponics cult ure 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 mu M Al3+ activity) by means of a split-plot design. Aluminum stress increased seedling tap root extensi on 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 her itable genetic variation for Al tolerance. The h(2) under HIAL was mod erate (0.57) on a single-replication basis and high (0.87) based upon five replicates, indicating the relative ease by which Al tolerance ma y be improved. Tolerance expressed as percent of control (PC) had a si milar h(2). Approximately 6% of the F-4-derived progeny in this study were numerically similar to the parents for Al response under HIAL, su ggesting that three to five genes may control Al tolerance and that a population size of 150 random inbred lines may be needed to assure ful l recovery of Al tolerance in the progeny of future breeding populatio ns. Expected gain and risk avoidance analysis suggested that two or th ree replications are sufficient for initial screening of single seed d escent (SSD) populations derived from the PI 416937 and that employmen t of this PI as a control enhances the ability of the breeder to disca rd inferior types during screening. Practical advice is presented to a ssist plant breeders in the efficient improvement of Al tolerance in s oybean.