1a. Objectives (from AD-416):
Identify oil and meal traits and the genes that influence those traits to improve the quality and value of U.S. soybeans.
1b. Approach (from AD-416):
The proposed studies will build on our observation that pod position along the main stem affects seed composition (protein:oil content) and seed quality (fatty acid composition of the oil and relative content of sulfur-containing amino acids in protein) and that these differences vary among soybean varieties. We will monitor seed fill duration (SFD) as a function of stem position in relation to seed composition. A second parallel but independent approach will be to screen the USDA Soybean Germplasm Collection to identify higher-oil germplasm that also contains adequate protein (to produce a 48% meal) and with high relative S-content. Accessions identified will be used for crosses to generate segregating populations to select genotypes that have increased seed quality. Digestibility and feed efficiency will be examined in chicken feeding experiments conducted in collaboration with colleagues at the University of Illinois.
3. Progress Report:
We investigated two specific conditions that are known to affect seed composition as possible factors contributing to the canopy position effects. The first was seed fill duration (SFD). It is generally thought that protein begins to accumulate before oil and therefore the longer the period of seed filling, the greater the content of oil. Consequently, we wondered whether seeds at the bottom of the canopy fill over a longer period that those at the top of the canopy. That was indeed observed with all ten genotypes being studied, and the difference in SFD from top to bottom ranged from 4 to 8 days. Qualitatively these results are consistent with the canopy position effects on composition but quantitatively cannot explain the differences among genotypes. One factor that may be contributing to this disparity is pod temperature, which one would assume would be equal among genotypes and simply a function of ambient temperature, but recent results suggest that may not be the case. Future studies will follow up the observation that under similar environmental conditions, pod temperatures can vary substantially among genotypes (up to 2°C).