The soybean aphid [Aphis glycines Matsumura (Hemiptera: Aphididae)] is an invasive insect pest of soybean [Glycine max (L.) Merr.] that was first reported in North America in 2000. There are currently no reports of soybean aphid biotype diversity and this information is needed before aphid resistance genes are deployed. The objective of this research was to test for aphid biotype variation. The response of two A. glycines isolates, one collected in Ohio and the other in Illinois, were compared by infesting eight soybean genotypes in nonchoice tests. The same genotypes also were tested with the Ohio isolate using a choice test. In the nonchoice test, there was a significant (P < 0.0001) effect of aphid isolate, genotype, and a significant aphid isolate by soybean genotype interaction for the number of aphids per plant 10 and 15 d after infestation. The responses of the eight genotypes to the Ohio isolate in the choice test were similar to their responses in nonchoice tests. PI 200538 and PI 567597C were resistant to both the Ohio and Illinois isolates and will be useful sources of resistance to both isolates. These tests confirm that there are at least two distinct biotypes of A. glycines in North America.

The soybean aphid (Aphis glycines Matsumura) is a major soybean [Glycine max (L.) Merr.] insect pest. Soybean plant introduction (PI) 200538 has strong resistance to the aphid. The objectives of our research were to determine the inheritance of resistance and to map gene(s) controlling resistance in PI 200538. F2 populations developed from crosses between PI 200538 and three susceptible genotypes were tested for resistance and with DNA markers. F2 plants from the cross ‘Ina’ × PI 200538 segregated 114 resistant to 37 susceptible and F2 plants from the cross ‘Williams 82’ × PI 200538 segregated 203 resistant to 65 susceptible when tested for resistance to soybean aphid biotype 1. F2 plants from the cross LD02‐4485 × PI 200538 segregated 167 resistant to 62 susceptible when tested for resistance to biotype 2. These populations fit a 3:1 genetic ratio (P = 0.89, 0.78, and 0.52, respectively) with resistance dominant over susceptibility. Segregation among F2:3 families from the crosses supported the dominant resistance gene hypothesis. The gene mapped to soybean linkage group F, flanked by the simple sequence repeat marker loci Satt510, Soyhsp176, Satt114, and Sct_033, located in the same region as the aphid resistance gene Rag2 Since the resistance gene in PI 200538 also gave resistance to soybean aphid biotypes 1 and 2, it is possible that the gene is Rag2 and not a new aphid resistance gene. Therefore, PI 200538 may be an additional source of Rag2

The discovery of biotype diversity of soybean aphid (SA: Aphis glycines Matsumura) in North America emphasizes the necessity to identify new aphid-resistance genes. The soybean [Glycine max (L.) Merr.] plant intro-

The soybean aphid (Aphis glycines Matsumura) is an important soybean [Glycine max (L.) Merr.] pest in North America. The dominant aphid resistance gene Rag1 was previously mapped from the cultivar 'Dowling' to a 12 cM marker interval on soybean chromosome 7 (formerly linkage group M). The development of additional genetic markers mapping closer to Rag1 was needed to accurately position the gene to improve the eVectiveness of markerassisted selection (MAS) and to eventually clone it. The objectives of this study were to identify single nucleotide polymorphisms (SNPs) near Rag1 and to position these SNPs relative to Rag1. To generate a Wne map of the Rag1 interval, 824 BC 4 F 2 and 1,000 BC 4 F 3 plants segregating for the gene were screened with markers Xanking Rag1. Plants with recombination events close to the gene were tested with SNPs identiWed in previous studies along with new SNPs identiWed from the preliminary Williams 82 draft soybean genome shotgun sequence using direct re-sequencing and gene-scanning melt-curve analysis. Progeny of these recombinant plants were evaluated for aphid resistance. These eVorts resulted in the mapping of Rag1 between the two SNP markers 46169.7 and 21A, which corresponds to a physical distance on the Williams 82 8£ draft assembly (Glyma1.01) of 115 kilobase pair (kb). Several candidate genes for Rag1 are present within the 115-kb interval. The markers identiWed in this study that are closely linked to Rag1 will be a useful resource in MAS for this important aphid resistance gene.

Phenotypic plasticity describes the range of phenotypes produced by a single genotype in different environments. We quantified the extent of phenotypic plasticity (evaluated as responsiveness to varying environmental conditions) of thermal time to heading and grain yield in 299 hard winter wheat (Triticum aestivum L.) genotypes from the US Great Plains. The genotypes, which included advanced breeding lines and recent and historic cultivars, were evaluated in 11 environments in 2011–2012 and 2012–2013. The average number of days from 1 January to heading across environments ranged from 109 to 150, and the cumulative growing degree days (GDD) from 1 January to heading ranged from 730 to 1112 GDD. Environmental mean grain yield varied from 1.3 to 5.3 Mg ha−1. Plasticity of GDD (GDDP) was strongly correlated with GDD (r = 0.81, P < 0.001), especially maximum GDD (r = 0.90, P < 0.001) across environments, indicating genotypes with greater plasticity developed later, especially within the earliest environments. Plasticity of GDD was negatively associated with yield (r = −0.58, P < 0.001) and therefore detrimental in the germplasm and environments evaluated. Yield plasticity of a genotype was positively correlated with its maximum (r = 0.80, P < 0.001) and minimum (r = 0.33, P < 0.001) grain yield across environments, indicating greater plasticity was favorable under optimal conditions, without a penalty under low‐yielding conditions. More than a century of wheat breeding in this region suggests GDDP has declined and yield plasticity has increased at similar rates. This is encouraging because it indicates the favorable plasticity traits (high yield plasticity, low GDDP) have been selected for indirectly and would respond to further selection.