Assessing stink bug resistance in soybean breeding lines containing genes from germplasm IAC-100.

Sixty-five soybean, Glycine max (L.) Merr., breeding lines containing the stink bug resistant 'IAC-100' in their pedigrees were evaluated for their resistance to stink bug, primarily southern green stink bug, Nezara viridula L., feeding in replicated field trials from 2001 to 2005. Plots were sampled throughout the season for stink bug abundance, and, at harvest, seed samples were rated for stink bug-induced kernel damage. Individual seeds were categorized as having none, light, moderate, or heavy damage plus 100-seed wt and plot yields were determined. Both ground cloth and sweep net sampling procedures were used to compare stink bug densities between the soybean entries. Stink bug densities varied between years; however, in the years when populations exceeded four per row-meter or six per 25 sweeps, there were more damaged soybean seeds (>25%) in the entries with higher stink bug numbers. During the first 2 yr of evaluations, the mean stink bug-damaged soybean seeds ranged from 10.0 to 38.2%. From these differential responses, 28 entries were selected for continued study in 2003-2004. In 2003, stink bug-damaged soybean seeds were low, with damage ranging from 2.9 to 18.2%. In 2004, stink bug damage ranged from 8.8 to 53.2%. From these 28 lines, 12 entries were selected for an advanced field screening trial in 2005, including the IAC-100 and 'Hutcheson'. Damaged soybean seeds ranged from 18.5 to 54.1% among these 12 entries in 2005, under heavy stink bug pressure. From these evaluations, four breeding lines with either Hutcheson X IAC-100 or IAC-100 x 'V71-370' in their genealogy were identified as possible breeding material for future soybean stink bug resistance cultivar development.

Evaluating lepidopteran defoliation resistance in soybean breeding lines containing the stink bug (Hemiptera: Pentatomidae) resistance IAC-100 cultivar in their pedigrees.

Sixty-five soybean, Glycine max (L.) Merrill, breeding lines containing 'IAC-100' in their pedigrees were evaluated for their resistance to lepidopteran defoliation in replicated field trials during 2001-2005. Three soybean cultivars, IAC-100 (with resistance to stink bug [Hemiptera: Pentatomidael feeding), 'Dillon', and 'Hutcheson', also were included in the evaluations. The percentage defoliation among these 68 entries ranged from 4.3 to 28.3% in 2001 and from 35.0 to 99.0% in 2002. Lepidopteran caterpillars, primarily Anticarsia gemmatalis Hiibner, but also some Pseudoplusia includens (Walker) and Hypena scabra (F.), peaked at 14.3 per row-meter on 11 September 2001 and at 39.7 per row-meter on 22 August 2002. Twenty-six entries with better resistance potential, plus two cultivars, were selected for continued evaluations in 2003 and 2004. Defoliation ranged from 23.3 to 56.7% among the 28 entries in 2003 and from 16.3 to 42.5% in 2004, with peak caterpillar densities of 20.3 per row-meter on 17 September 2003 and 14.5 per row-meter on 8 September 2004. From these differential responses, 12 entries were included for advanced resistance evaluations in 2005. The breeding line entries 52 (IAC-100 X V89-1301), 23 (IAC-100 X V89-1301), and 14 (IAC-100 X V71-370), plus entry 37 (IAC-100) had lower defoliation rankings during all 5 yr of this study, with the entry having the lowest defoliation ranked 1 and the entry with highest defoliation ranked either 68, 28, or 12, based on the number of entries evaluated each year. The overall mean rankings of these four entries over the 5 yr of this study were 4.4, 3.0, 4.2, and 4.6, respectively. A fifth entry, 30 (IAC-100 x V71-370), was in the top group with lower defoliation in 4 yr of this 5-yr study, and it had an overall mean ranking of 5.6. A sixth entry, 35 (Hutcheson X IAC-100), had moderate resistance (overall ranking of 19.2) compared with the standard Hutcheson (30.8 ranking of a possible highest ranking of 40.8). Entry 35 also yielded as well as the standard cultivars evaluated in the study. These lines will provide excellent sources for future soybean germplasm and varietal resistance development.

Genetic and Phenotypic Analysis of Soybean mosaic virus Resistance in PI 88788 Soybean.

ABSTRACT Resistance to Soybean mosaic virus (SMV) was identified in PI 88788 soybean, a germ plasm accession from China that is used widely as a source of resistance to soybean cyst nematode. Strains SMV-G1 through -G7 infected the inoculated leaves of PI 88788 but were not detected in upper, noninoculated trifoliolate leaves. Inheritance of resistance was determined by inoculating progenies of crosses of PI 88788 with susceptible cvs. Essex and Lee 68 with SMV strains G1 and G7. Allelomorphic relationships with known genes for resistance to SMV were tested in crosses with the resistant genotypes PI 96983, L29, and V94-5152, possessing Rsv1, Rsv3, and Rsv4 genes, respectively. Data analyses showed that resistance in PI 88788 to SMV-G1 is controlled by a single, partially dominant gene; however, to SMV-G7, the same gene was completely dominant. The PI 88788 gene was independent of the Rsv1 and Rsv3 loci, but allelic to Rsv4 in V94-5152. Expression of the Rsv4 gene in PI 88788 resulted in a reduced number of infection sites and restricted short- and long-distance movement of virus, rather than hypersensitivity. A unique late susceptible phenotype was strongly associated with heterozygosity. This gene has potential value for use in gene pyramiding to achieve resistance to several SMV strains, as well as for rate-reducing resistance.