Optimizing regeneration protocols for native Seeds of Success–collected milkvetch (Astragalusspp.) genetic resources

Abstract The USDA ARS National Plant Germplasm System conserves and promotes the use of important agricultural and ecological plant germplasm. In these collections, ~23,000 accessions representing 147 plant families have been acquired through the Bureau of Land Management Seeds of Success program. Unlike many of the cultivated crops in the collections, a significant proportion of these species lack basic biological information necessary for seed regeneration and long-term conservation. To fill knowledge gaps, we studied 5 native milkvetch (Astragalus L. [Fabaceae]) species to optimize germination protocols, characterize phenological and phenotypic traits, and test pollinator efficiency using various pollinator treatments. Germination trials tested 3 cold stratification (0, 2, or 6 wk in 4 °C [40 °F]) and 2 germination temperature (low: 15/25 °C [59/77 °F] and high: 20/30 °C [68/86 °F]) treatments in a full factorial design. Germination trial seedlings were outplanted at 2 sites (Prosser and Pullman, Washington) in fall 2020. We evaluated 3 pollination methods using honeybee (Apis mellifera Linnaeus [Apidae]), alfalfa leafcutting bee (Megachile rotunda Fabricius [Megachilidae]), and open pollination. Cold stratification increased germination in A. drummondii but had little effect on the other 4 species. Germination at the lower incubation temperatures was as effective, if not better, than germination at the higher temperatures. Only Canadian milkvetch (Astragalus canadensis L.) and two-grooved milkvetch (A. bisulcatus (Hook.) A. Gray) had sufficient survival in the Pullman location to move forward with pollinator treatments. Differences were not found in pollinator treatments for seed set or yield (P > 0.05). Astragalus canadensis and A. bisulcatus performed generally better than other species evaluated with the highest number of established and surviving plants, good seed set, and highest seed yields. This research provides critical information on germplasm management and suggests the need for further research on protocol development.