Location: Plant Introduction Research2012 Annual Report
1a. Objectives (from AD-416):
Characterize the molecular structure of starch granule formation, and develop analytical methods to identify germplasm for high digestibility and resistant starch. Secondly, characterize GEM germplasm for starch nutritional value (for humans and livestock), biofuel potential, and ethanol yield.
1b. Approach (from AD-416):
Ethanol fermentation tests, and starch digestibility analysis will be conducted on GEM germplasm previously identified with high starch content and/or ethanol content. In addition, other sources of germplasm will be analyzed for resistant starch content. Analytical methods including differential scanning calorimetry (DSC) will be studied to determine applicability for identifying GEM germplasm with desirable starch attributes. The identified germplasm will be recombined for future trials as hybrids, and new breeding crosses made and evaluated.
3. Progress Report:
This project relates to the primary objectives of the parent project which include the development, evaluation, and methodology to release germplasm with resistant starch, high digestibility, and ethanol potential. Previous studies (2009 and 2010) on waxy and normal corn inbreds indicated that waxy germplasm had higher starch hydrolysis rates than normal inbreds (92.4% vs 88.3% for normal). This was attributed to lower amylose content found in waxy which increases starch hydrolysis. As a follow-up to that research two waxy hybrids, GEMS-0185 x GEMN-0186, and GEMS-0206 x GEMN-0186 (11GEM07047 and 11GEM07046 respectively) were studied and compared to the inbred waxy parent lines (GEMS-0185 and GEMN-0186). GEMN-0186 gave lower ethanol yield (30.4%) and lower starch content (57.2%) than the other three genotypes (11GEM07047, 11GEM07046, GEMN-0185) which ranged from 34.0-34.3% for ethanol yield and 64.0-64.3% for starch content. The hybrid, GEMS-0185 x GEMN-0186 showed a substantially larger 100-kernel weight (33.6g) than either of its parent lines (27.0g for GEMS-0185; 21.3g for GEMN-0186). Hybrid GEMS-0185 x GEMN-0186, also had similar starch content (63.8%) to the high parent line GEMS-0185 (64.0%) and greater than the other parent line GEMN-0186 (57.2%). The results indicated that the F1 waxy hybrid had greater starch content and 100 kernel weight than the low parent line and may potentially be useful for ethanol production. Preliminary studies were initiated in collaboration with Truman State University on characterization of ae wx mutants for resistant starch (RS), and slowly digestible starch (SDS). RS and SDS are both important for health by reducing glycemic index, and SDS may provide prolonged energy since starch becomes slowly available. While RS is attributed to the presence of high amylose, SDS is attributed to the presence of long branch chains of amylopectin. Four ae wx genotypes were compared to one ae check inbred, and the normal inbred, B73. The normal inbred B73 was almost exclusively rapidly digestible starch (RDS), 98.2%. The ae inbred was 25.3% RS, and 5.2% SDS, and 69.5% RDS; while the four ae wx inbreds averaged 4.2-8.1% RS, 6.7-7.9% SDS, and 84.0-88.2% RDS. The results suggest that ae wx genotypes have greater levels of SDS, while ae is greater for levels of RS.