Branch number is one of the main factors affecting the yield of soybean (Glycine max (L.)). In this study, we conducted a genome-wide association study combined with linkage analysis for the identification of a candidate gene controlling soybean branching. Five quantitative trait nucleotides (QTNs) were associated with branch numbers in a soybean core collection. Among these QTNs, a linkage disequilibrium (LD) block qtnBR6-1 spanning 20 genes was found to overlap a previously identified major quantitative trait locus qBR6-1. To validate and narrow down qtnBR6-1, we developed a set of near-isogenic lines (NILs) harboring high-branching (HB) and low-branching (LB) alleles of qBR6-1, with 99.96% isogenicity and different branch numbers. A cluster of single nucleotide polymorphisms (SNPs) segregating between NIL-HB and NIL-LB was located within the qtnBR6-1 LD block. Among the five genes showing differential expression between NIL-HB and NIL-LB, BRANCHED1 (BRC1; Glyma.06G210600) was down-regulated in the shoot apex of NIL-HB, and one missense mutation and two SNPs upstream of BRC1 were associated with branch numbers in 59 additional soybean accessions. BRC1 encodes TEOSINTE-BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS 1 and 2 transcription factor and functions as a regulatory repressor of branching. On the basis of these results, we propose BRC1 as a candidate gene for branching in soybean.

The Raso2 , novel QTL for Korea biotype foxglove aphid resistance in soybean from PI 366121 was identified on chromosome 7 using GoldenGate SNP microarray. Foxglove aphid, Aulacorthum solani (Kaltenbach), is a hemipteran insect that infects a wide variety of plants worldwide and causes serious yield losses in crops. The objective of this study was to identify the putative QTL for foxglove aphid resistance in wild soybean, PI 366121, (Glycine soja Sieb. and Zucc.). One hundred and forty-one F₄-derived F₈ recombinant inbred lines developed from a cross of susceptible Williams 82 and PI 366121 were used. The phenotyping of antibiosis and antixenosis resistance was done through choice and no-choice tests with total plant damage and primary infestation leaf damage; a genome-wide molecular linkage map was constructed with 504 single-nucleotide polymorphism markers utilizing a GoldenGate assay. Using inclusive composite interval mapping analysis for foxglove aphid resistance, one major candidate QTL on chromosome 7 and three minor QTL regions on chromosomes 3, 6 and 18 were identified. The major QTL on chromosome 7 showed both antixenosis and antibiosis resistance responses. However, the minor QTLs showed only antixenosis resistance response. The major QTL mapped to a different chromosome than the previously identified foxglove aphid resistance QTL, Raso1, from the cultivar Adams. Also, the responses to the Korea biotype foxglove aphid were different for Raso1, and the gene from PI 366121 against the Korea biotype foxglove aphid was different. Thus, the foxglove aphid resistance gene from PI 366121 was determined to be an independent gene from Raso1 and was designated as Raso2. This result could be useful in breeding for new foxglove aphid-resistant soybean cultivars.

We investigated several characteristics of the development and reproduction of the aphid Aulacorthum solani raised on soybean (Glycine max) at 10 constant temperatures between 2.5 and 30 °C, and described the relationship between temperature and several critical biological characteristics using mathematical models. We found that A. solani could survive and reproduce on soybean at temperatures ranging from 5 to 27.5 °C. High fecundity was observed at temperatures from 12.5 to 20 °C. The lower developmental threshold and thermal constant for this species’ nymphal stages were estimated to be 5.02 °C and 131.2 degree-days, respectively, using a linear model. The upper developmental threshold was estimated to be 33.9 °C using the Lactin-2 model. The optimum temperature for nymphal development was estimated to be 26.9 °C. The maximum total fecundity was estimated as ca. 76.9 nymphs per adult at 18.1 °C. The daily fecundity sharply increased at earlier adult ages, and slowly decreased thereafter until final parthenogenesis occurred, over a range of temperatures from 12.5 to 25 °C. The maximum daily fecundity was estimated to be ca. 6.1 nymphs per adult per day for a 5.2 day old of adult at 21.3 °C using an age- and temperature-dependent model of adult fecundity. In terms of life table statistics, the intrinsic rates of increase and the finite rate of increase were both highest at 25 °C, while the net reproductive rate was highest at 20 °C.