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 crop 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 determined the heritability of the trait in a cross with Young, a highly productive Al-sensitive cultivar. The objective of the present study was to identify quantitative trait loci (QTL) which condition Al tolerance by a genetic 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 parents 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 experimental design. Aluminum tolerance was defined as (i) root extension under DIAL conditions, and (ii) root extension as a percentage of control [PC = (HIAL/NOAL) X 100]. Multiple regression analysis revealed five QTL from independent linkage groups which conditioned root extension under HIAL stress. Three of the five QTL were also detected by PC as the expression of Al tolerance. While most alleles for Al tolerance were derived from the AI-tolerant 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 stress. At present, it is not known whether the Al tolerance gene from Young, in combination with those from PI 416937, will raise Al tolerance beyond that now observed in the PI. One allele for Al tolerance from PI 416937 (for marker B122-1) may be difficult to capitalize upon, agronomically, because of its association with a detrimental pod dehiscence factor. Further experimentation is needed to distinguish between linkage and pleiotropic effects near this marker. A favorable epistatic effect for Al tolerance was detected between two alleles from the PI 416937. The relationships revealed by marker analysis indicated that marker-facilitated selection may be a viable approach in the breeding of Al-tolerant soybean.