Cover Crop Diversity through Evaluation and Increase from Breeder Stocks and Germplasm Repositories

Cover Crop Diversity through Evaluation and Increase from Breeder Stocks and Germplasm Repositories

Summary

The focus of this study is to increase and evaluate germplasm of the leguminous cover crops Crotalaria juncea (sunn hemp), C. ochroleuca (slenderleaf rattlebox), Vigna unguiculata (cowpea), and Indigofera hirsuta (hairy indigo) that is not currently commercially available but has the potential for overcoming some of the constraints of existing commercial varieties such as hardseededness and the inability to set seed in Florida. This report confirms variation in the hardseededness trait in hairy indigo that supports the likelihood of further decreasing hardseededness in the cv. Flamingo. One accession of sunn hemp was successfully increased over the winter in Puerto Rico.

Objectives/Performance Targets

1. Multiply seeds of cover crop species and accessions with high potential for utility but are not currently available to obtain sufficient amounts for replicated field evaluation.

2. Select for the soft-seed trait in ‘Flamingo’ hairy indigo.

3. Evaluate on-station and on-farm for ecological services in comparison with commonly available species.

4. Provide recommendations and make seed available for the most promising species/accessions.

Accomplishments/Milestones

Recruitment

An undergraduate student worker and a research scholar were successfully recruited for the project and began work in summer and fall 2016, respectively. Work has been initiated on objectives one and two of the project.

Seed Multiplication

Seeds of C. juncea (PI 391567 and PI 426626) and C. ochroleuca (PI 274767 and PI 543869) were obtained from the USDA, ARS, Plant Genetic Resources Conservation Unit (PGRCU) in Griffin, GA. Approximately, 100 seeds of each accession were provided in response to our request. Since the timing was not appropriate for multiplying the seed in Florida, the seeds were sent to Puerto Rico for multiplication in fall 2016. Only the PI 391567 sunn hemp accession germinated well. Seed cleaning will be accomplished in April 2017 and approximately 2 lb of PI 391567 seed are expected and will be multiplied further in Florida in summer 2017.

Two consecutive crop failures have resulted in a lack of availability of the cowpea germplasm lines US-1136, US-1137, and US-1138. As an alternative, we have requested seeds for these cowpea lines from USDA, ARS, PGRCU (accessions PI 664531, PI 664532, PI 664533). Seeds received will be multiplied in Florida in summer 2017.

Propagation and Characterization of Hairy Indigo Seeds

In summer 2016, ‘Flamingo’ hairy indigo seeds that were stored in a freezer for more than two decades were assessed in a series of germination experiments. Although germination was very challenging without scarification, the researchers noticed a pattern in physical characteristics of seeds that were germinating better. Germinated seeds were placed in pots in greenhouse for establishment before transplanting the resulting seedlings in a field at the Agronomy and Forestry Research Unit (AFRU) in mid-summer (Figure 1). Seed pods were harvested from each plant at weekly intervals during fall 2016.

Assessment of Genotypic Variation in Hardseededness in Hairy Indigo

A laboratory study was conducted to assess genotypic variation in hardseededness in hairy indigo. Fourteen accessions of hairy indigo were secured from USDA ARS, PGRCU and were evaluated for variability in germination based on physical characteristics of seeds. Results confirmed genetic variation in seed coat permeability in this species (Table 1). The highest germination rate and percentage of soft seed were obtained with ‘Flamingo’ in comparison with the other accessions. This experiment will be repeated in spring 2017.

Seed germination tests were performed on seeds that were thought to be ‘Flamingo’ that were in storage in a freezer for ~ 30 years. The germination was very low (<15%) and scarification was required for better performance. The results suggest that we should rely on USDA, ARS as the seed source for subsequent work to further increase the percentage of soft seed in ‘Flamingo’.

Impacts and Contributions/Outcomes

The confirmation of genetic variability for the hard seed trait provides evidence that our proposed selection for soft seed should result in further reduction in the incidence of hard seed in this cultivar. A soft-seeded cultivar will eliminate the need for seed scarification and the problem of hard seed resulting in undesirable volunteers in cash crops. Involving growers in seed multiplication and field evaluation of the improved hairy indigo selection as well as the cowpea lines and Crotalaria spp. discussed above will promote greater seed availability and improve the prospects for commercialization and adoption of new cover crop options.

Collaborators: