2011 Annual Report
1a.Objectives (from AD-416)
Objective 1: Identify genetic factors controlling bean seed processing quality and consumer acceptance attributes and identify QTL(s) for related traits including seed coat color and appearance, hardness, and digestibility.
Objective 2: Characterize genetic diversity for seed traits that influence human nutritional value of bean including antioxidant, mineral, and antinutrient levels that contribute to digestibility, and identify QTL(s) and gene(s) responsible for seed zinc accumulation.
1b.Approach (from AD-416)
Develop a linkage map for a black bean recombinant inbred line population using SSR and SNP markers. Use this resource identify QTL involved in canning quality and color retention in thermally processed beans, and to identify the Asp gene responsible for seed coat shine. Develop rapid phenotypic screens to for canning quality with near infrared spectoscopy. Measure variability for nutrient composition, cooking time, and sensory characteristics of modern and historically important dry bean varieties in the Mesoamerican gene pool. Develop populations of EMS mutagenized beans. Screen mutant populations for lines with reduced levels of seed raffinose and stachyose oligosaccharides. Screen diverse germplasm for natural variability in seed oligosaccharide content. Identify genes involved in seed zinc accumulation and tolerance to low zinc soils via transcriptome profiling, gene expression analysis, and molecular mapping.
Processing quality was evaluated on 108 black bean lines that were grown in a replicated field experiment in 2010. The materials consisted of varieties and breeding lines and a population of inbred lines developed from two varieties with contrasting canning traits. One parental variety has a superior appearance and color retention but the seed takes up less water than desirable when canned. The other parent takes up sufficient water, but loses its black bean color during the canning process. The materials were canned and evaluated for color retention, texture, appearance and water uptake. These analyses revealed a negative correlation between water uptake and color retention, two desirable characteristics. This correlation was not absolute, however, and it was possible to identify lines with both good color retention and water uptake. To elucidate the genetic control of these processing quality traits, a linkage map is under development. This map currently contains one type of molecular marker. The materials were again planted in a replicated field experiment in 2011. The two years of processing quality data will be evaluated with the molecular marker data. In addition, we are testing near infrared spectroscopy as a new method to evaluate processing quality that will not require destructive sampling.
Field experiments were executed to understand if plant breeding for agronomical important traits such as seed yield and disease resistance has also resulted in unintended changes in nutrient makeup of the bean seed. Our findings suggest that seed protein content has decreased in some dry bean market classes, including red, black and pinto as compared to heirloom varieties. The decrease in seed protein in most, but not all cases was associated with an increased overall seed yield. Micronutrient content was found to vary significantly in bean varieties. One important finding of our work was that some bean varieties retain a greater percent of their minerals upon thermal processing than other varieties. The cellular basis for these differences will be explored. Since flavor is ever becoming more important to consumers, but often overlooked by bean breeders, a sensory evaluation protocol for cooked beans was developed and a pilot study was conducted with navy beans. More sensory evaluations are planned for the future.
Substantial progress has been made in the development of mutagenized bean populations. These populations will be used as genetic tools to understand how mutations in genes of interest change the plant phenotype. Thus far populations have been developed in select varieties in the two bean gene pools, the Andean and Mesoamerican. We currently have over 2500 mutant lines for each of three bean varieties that are ready to use for genetic screening.
Progress has been made in understanding the genetic control of zinc concentration in bean seeds. A genetic complementation test has revealed that the basis for low seed zinc in two bean varieties is two different genes. An analysis of the transcriptome of the developing pods of these two low seed zinc varieties and one high seed zinc variety is underway.
Identification and genomic location of ten zinc transporter genes in the dry bean genome. Zinc transporters (ZIP) are a family of proteins that transport zinc and other minerals within the plant and to the seed. Characterization of these genes is a useful step in the biofortification of plant foods with micronutrients essential to the human diet and often in short supply. ARS researchers in East Lansing, MI have identified ten members of the ZIP family in the dry bean genome via DNA sequence analysis. The position of these genes in the bean genome in relation to molecular markers was determined. One of these genes has been found to be linked to a region of the genome important for ferrous iron accumulation in bean seeds. This research will help bean breeders develop biofortified bean seeds using marker assisted selection.