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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.sub.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 µM [Al.sup.3+] activity solutions (NOAL and HIAL, respectively) employing Al levels as whole plots in a split-plot experimental design. Aluminum tolerance was defined as (i) root extension under HIAL 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 Al-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 HIAL 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., THE INCREASING DEMAND for agricultural lands throughout the world challenges soil scientists, plant breeders, and agronomists alike to improve the productivity of problem soils. The acid soils of the Brazilian [...]

In more than 25 yr since the discovery of soybean [Glycine max (L.) Merr.] resistance to defoliating insects, attempts to introgress this trait into elite germplasm have been relatively unsuccessful. Resistance to defoliating insects in soybean is expressed as a combination of antibiosis (toxicity) and antixenosis (nonpreference). Both of these resistance modes are inherited quantitatively in soybean. The objectives of this study were ii) to use restriction fragment length polymorphism (RFLP) maps to identify quantitative trait loci (QTLs) in soybean for antibiosis against corn earworm (CEW) (Helicoverpa zea Boddie), (ii) to determine the relative magnitude, gene action, and genomic locations of these QTLs, and (iii) to compare them to previously detected soybean antixenosis QTLs. Restriction fragment length polymorphism maps were constructed in three soybean [F.sub.2] populations segregating for antibiosis against CEW: `Cobb' x PI171451, Cobb x PI227687, and Cobb x PI229358. Antibiosis was measured as larval weight gain in a detached leaf assay. The RFIP data were associated with insect bioassay data to detect QTLs for antibiosis in each cross. Variance component heritability estimates for antibiosis in the three crosses were 54, 42, and 62% in Cobb x PI171451, Cobb x PI227687, and Cobb x PI229358, respectively. An antibiosis QTL on Linkage Group (LG) M was detected in both Cobb x PI171451 and Cobb x PI229358 ([R.sup.2] values of 28 and 22%, respectively). An antixenosis QTL was also significant at this location in the same two crosses. This was the only insect-resistance QTL that was detected for both antibiosis and antixenosis. Antibiosis QTLs were also detected on LGs F and B2 in Cobb x PI227687 ([R.sup.2] = 33 and 12%, respectively), and LGs G and J in Cobb x PI229358 ([R.sup.2] = 19% for each). Antibiosis was conditioned by the PI (resistant parent) allele at the QTLs on LGs G, M, and B2, whereas the susceptible parent, Cobb, provided antibiosis alleles at the QTLs on LGs F and J., PLANT RESISTANCE TO INSECTS (PRI) has been a difficult trait for soybean breeders to efficiently introgress into elite cultivars. In more than 25 yr since high levels of PRI were [...]