Covering Ground: Southern Native Leguminous Summer Tepary Beans to Boost Productivity of Organic Spinach

View the project final report

Commodities

• Vegetables: greens (leafy), Spinach, Tepary beans

Practices

• Crop Production: cover crops, crop improvement and selection, cropping systems, nutrient management
• Production Systems: organic agriculture, transitioning to organic
• Soil Management: soil analysis, soil microbiology, soil quality/health

Cover crops are essential for improving soil health, enhancing nutrient availability, and reducing management costs for subsequent main crops. However, most organic growers in the southern United States leave fields fallow during summer because of the limited availability of regionally adapted cover crops that can tolerate high temperatures. Tepary bean (Phaseolus acutifolius) is a promising alternative due to its adaptation to hot, dry regions, nitrogen-fixing ability, and potential to improve soil fertility for succeeding crops.

This project evaluated the genetic potential of USDA tepary bean germplasm for various agronomic and nutritional traits and compared summer legume cover crops for their effects on soil microbial communities. The goal was to identify genetic resources and improve understanding of plant-soil interactions to support the development and adoption of summer cover cropping systems for sustainable vegetable production. A panel of USDA tepary bean accessions was evaluated under field conditions using an augmented experimental design. Agronomic and nutritional traits, including biomass production, flowering time, nitrogen-related characteristics, and leaf and seed amino acid concentrations, were measured. Genotyping-by-sequencing (GBS) data were integrated with phenotypic observations to perform genome-wide association studies (GWAS) and identify genomic regions associated with important agronomic traits. In parallel, a comparative field study evaluated summer legume cover crops such as cowpea, sunn hemp, and tepary bean to determine their influence on rhizosphere microbial communities using high-throughput sequencing. Soil microbial composition and functional potential were characterized to understand how different cover crop species influence soil health and microbial communities.

This project identified significant genetic variation among tepary bean accessions for traits including biomass, flowering time, nitrogen-related traits, and other agronomically important characteristics. GWAS identified genomic regions and candidate genes associated with these traits, providing valuable inputs for future breeding efforts. The rhizosphere microbiome study demonstrated that summer legume cover crops support distinct microbial communities with functions related to nutrient cycling and soil health. Although our project primarily generated foundational research, these findings provide practical guidance for adopting tepary bean and other summer legume cover crops in organic vegetable production, supporting the future development of improved tepary bean cultivars and cover cropping systems in the southern United States.

1. To evaluate the USDA tepary bean (Phaseolus acutifolius) accessions under organic field conditions and identify genomic regions associated with agronomically and nutritionally important traits, using genome-wide association studies (GWAS).
2. To compare summer legume cover crops (tepary bean, cowpea, and sunn hemp) for their effects on soil microbial communities, soil health, and the productivity of subsequent organic spinach production.

Objective 1: A panel of tepary bean accessions was phenotyped under organic production conditions for key agronomic and physiological traits. Phenotypic data were integrated with genotyping-by-sequencing (GBS) data to perform GWAS and identify significant marker-trait associations. This work provided valuable genomic resources and candidate genes to support future breeding efforts to develop tepary bean cultivars suitable for sustainable agricultural systems.

Objective 2: A comparative field study evaluated tepary bean alongside other summer legume cover crops (cowpea and sunn hemp) to determine their influence on rhizosphere microbial composition and functional potential using amplicon sequencing. Soil health indicators and crop performance were assessed to understand how different cover crop species contribute to nutrient cycling and sustainable production. The results provide insights into selecting cover crop species that improve soil health and support organic cropping systems.