Development and Phenotypic Evaluation of a Brassica oleracea Leafy Greens Diversity Panel

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Commodities

• Vegetables: greens (leafy)

Practices

• Crop Production: crop improvement and selection, plant breeding and genetics
• Pest Management: genetic resistance

Collard greens are primarily produced in the Southern region where they are an important cultural heritage crop. Brassica oleracea leafy greens, including collard greens and kale, are an exceptional source of vitamins, minerals, and phenolic compounds. However, research on these crops is limited leading to reduced availability and use of genetic resources for Brassica leafy greens. Despite the increasing popularity of collard greens and kale, the number of cultivars available for their production remains low. In addition, production is challenged by high insect and disease pressure, and the emergence of new pathogenic strains of economically important diseases (Bacterial leaf blight, Alternaria leaf spot) emphasizing the need for improved cultivars. We propose to develop a B. oleracea leafy green diversity panel from public germplasm sources, including the USDA-NPGS collection and the Seed Savers Exchange (SSE). The developed diversity panel, BLG1, would be a valuable source of alleles for improved nutrition (high glucosinolates), biotic (diseases and pests) and abiotic (salinity and high temperature) stress resistance for B. oleracea breeding programs. Release of new, improved cultivars would increase sustainability and profitability of Brassica leafy greens production through reduction of pesticide usage combined with increased yields.

The main goal of this project is to develop a collection of B. oleracea leafy green accessions (collected from USDA-NPGS and the Seed Savers Exchange) to identify desirable alleles and facilitate their introgression into improved collard and kale cultivars for production in the Southeastern US. The transition of these accessions into more stable, homozygous lines will improve their utility for future breeding and genetics research projects. The long-term goals of these projects are to (i) genotype the diversity panel (BLG1) and map the genomic regions associated with biotic and abiotic stress resistance, and nutrition using genome-wide association studies (GWAS); (ii) develop new B. oleracea-leafy green cultivars with better horticultural traits and resistance; (iii) introgression of desirable alleles from these accessions to other economically important B. oleracea species like cabbage.

We have already self-pollinated 260 accessions (S0) once and have S1 seeds for each accession. Keeping this in mind our major objective will be to purify these accessions for one more season to obtain S2 seeds. Towards the fall 2023, phenotyping of each BLG1 individual will be done for different horticultural traits and the records will be maintained.

The proposed proposal has been formulated for these objectives:

Objective 1: Self-pollination and seed increase of the collected accessions during the first year, 2022-23
In fall 2022, single seeds of each accession (S1) will be sown to obtain S2 seeds for phenotyping to reduce segregation (i.e., to generate ‘true  breeding’ seed) within each accession. Manual pollination will be carried out to ensure selfing for all 260 accessions of the diversity panel. This will be done in greenhouses available at Clemson University Coastal Research and Education Center (CREC) in Charleston, SC.

Objective 2: Phenotypic evaluation of all the S2 genotypes for different horticultural traits and disease resistance during the second year, 2023-24
Two replications of 10 seeds for each S2 accession will be seeded for field trials in Fall 2023 and Spring 2024 to evaluate the morphological diversity of all the accessions (collard, kale and non-heading cabbage), including leaf shape, leaf texture, leaf color, days to bolting and days to flowering. In addition to the field trials, the S2 kale genotypes will be screened for resistance against Alternaria leaf spot (Alternaria sp.). Alternaria leaf spot is the most important fungus on organic kale in South Carolina esp. in fall and the cultivars ‘Darkibor’ and ‘Winterbor’ are susceptible to the new causal agent, A. japonica (Keinath et al. 2021). The kale accessions in BLG1 (N=50) will expand the germplasm available for disease screening increasing the likelihood of identifying resistance sources.