Aluminum tolerance associated with quantitative trait loci derived from soybean PI 416937 in hydroponics

Acid soils with high levels of Al impede root growth, causing increased cro p sensitivity to drought and decreased nutrient acquisition. Development of Al-tolerant cultivars may be a cost effective response to the problem. In previous investigations, we identified an Al-tolerant soybean [Glycine max (L.) Merr.] plant introduction from Japan (PI 416937), and subsequently det ermined the heritability of the trait in a cross with Young, a highly produ ctive Al-sensitive cultivar. The objective of the present study was to iden tify quantitative trait loci (QTL) which condition Al tolerance by a geneti c linkage map of 155 restriction fragment Length polymorphism (RFLP) marker loci and a hydroponics-based Al response. The 120 F-4-derived progeny from Young X PI 416937 were divided into four sets and evaluated with the paren ts for tap root extension in 0 and 2 mu M Al3+ activity solutions (NOAL and DIAL, respectively) employing Al levels as whole plots in a split-plot exp erimental design. Aluminum tolerance was defined as (i) root extension unde r DIAL conditions, and (ii) root extension as a percentage of control [PC = (HIAL/NOAL) X 100]. Multiple regression analysis revealed five QTL from in dependent linkage groups which conditioned root extension under HIAL stress . Three of the five QTL were also detected by PC as the expression of Al to lerance. While most alleles for Al tolerance were derived from the AI-toler ant parent, PI 416937, a RFLP allele from Young (for marker EV2-1) improved Al tolerance expressed as PC and exhibited a similar trend under DIAL stre ss. At present, it is not known whether the Al tolerance gene from Young, i n combination with those from PI 416937, will raise Al tolerance beyond tha t now observed in the PI. One allele for Al tolerance from PI 416937 (for m arker B122-1) may be difficult to capitalize upon, agronomically, because o f its association with a detrimental pod dehiscence factor. Further experim entation is needed to distinguish between linkage and pleiotropic effects n ear this marker. A favorable epistatic effect for Al tolerance was detected between two alleles from the PI 416937. The relationships revealed by mark er analysis indicated that marker-facilitated selection may be a viable app roach in the breeding of Al-tolerant soybean.