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

Commodities

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

Practices

• Crop Production: cover crops, crop improvement and selection, cropping systems, nutrient management
• Production Systems: organic agriculture
• Soil Management: 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.