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

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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

Climate-resilient summer cover crops are critical to improve soil health, enhance nutrient availability, and reduce the management cost of the following winter crops. The proposal focuses on exploring the potential of southern native tepary beans (Phaseolus acutifolius) as an alternative summer and effective leguminous cover crop to enhance the productivity of winter organic spinach. Most organic growers leave the soils barren due to the limited availability of regionally adapted cover crops. Tepary beans represent the best-untapped option as a cover crop that is (1) native to southern Texas and Mexico, (2) heat and drought-stress tolerant, and (3) leguminous crop mobilizing nitrogen in the available zone to benefit the succeeding organic winter vegetables like spinach. We will evaluate the 211 USDA undomesticated accessions of the tepary beans under organic production by assessing their productivity, nodulation properties, and nitrogen-fixing potential by measuring ureides (allantoin and allantoate) uptake in summer using augmented field design. The phenotypic data will be used for genome-wide association analysis (GWAS) to allow the mapping of genes associated with these traits and develop the best varieties through introgression breeding. Simultaneously, a comparative study of legume cover crops will be performed using split-plot designs to assess their impact on soil health by analyzing physicochemical properties, bulk soil microbiome diversity, and the productivity of winter-grown spinach varieties. The outcome of this study would demonstrate the genetic potential of southern-adapted tepary beans and open opportunities to promote the rapid adoption of leguminous cover crops by the regional organic vegetable industry.

1. Identify tepary bean accessions best suited for organic summer production based on (a) adaptability to organic production, (b) nitrogen-fixing potential,
2. Identify the best combinations of leguminous cover crops (tepary beans, Sun hemp, cowpeas) and fall cash crop spinach based on spinach productivity, nitrogen use efficiency (NUE), and soil microbiome diversity.

Objective 1 will focus on performing phenotypic screening of tepary bean accessions under an organic system using augmented filed plot design and commercial checks due to limited seed availability. The field evaluation under organic production would rely on assessing a diverse range of USDA accessions for critical agronomic traits such as biomass production, nitrogen fixation capacity, and adaptability to regional challenges such as drought tolerance, disease resistance, and weed suppression. The outcome of objective 1 would be identifying accessions exhibiting superior performance under organic environmental conditions and management practices. The trait data collected will be used to characterize existing phenotypic variations landscape among accessions to pinpoint traits of interest for further genetic analysis. As a sub-part of objective 1, a Genome-Wide Association Study (GWAS) will be performed by extracting DNA from all accessions, followed by high-throughput genotyping (ddRAD) to analyze genetic variation across all accessions. The GWAS will be performed using established statistical analyses to identify associations between specific genetic markers (Single Nucleotide Polymorphisms, SNPs) and observed phenotypic traits. As a deliverable, we anticipate uncovering genomic regions and candidate genes responsible for expressing desired agronomic traits, providing insights into the genetic basis of tepary bean performance. This primary study's long-term goal will help facilitate the selection of promising accessions and genetic markers for targeted breeding efforts to develop improved cover crop varieties with enhanced productivity, resilience, and ecological benefits.

With objective 2 we will undertake a comparative study to evaluate the efficacy of the commercially available native and domesticated varieties of tepary beans vis-à-vis two other legume cover crops. These selected varieties will be grown in a split-plot design followed by a set of regionally popular spinach varieties. The goal of objective 2 is to assess the potential of tepary beans to enhance soil microbial diversity and productivity of spinach. The same plots will be used for spinach production in the fall to evaluate spinach's biomass potential and nitrogen uptake efficiency. The soil microbiome diversity will be assessed based on the bulk soil amplicon sequencing before and after cover plot planting and at the end of spinach harvest. The comparative impact of tepary bean and cover crop species on soil health will be monitored by performing soil chemical analysis (elemental nitrogen (TKN), free nitrates, organic matter, and mineral composition) and physical properties.