Dry after-ripening increases germination of critically imperilled Physaria thamnophila (Zapata bladderpod)

Abstract

Effective endangered plant conservation and recovery require empirical knowledge of seed dormancy release and responses to post-collection handling, yet such information is lacking for many rare taxa. Physaria thamnophila (Zapata bladderpod; Brassicaceae), a critically imperilled (G1) species endemic to southern Texas, USA, is poorly studied, and basic questions regarding seed storage and germination remain unresolved. We evaluated the effects of short-term cool-storage duration (14–180 d), storage temperature (refrigeration vs. freezing), dry after-ripening and maternal plant identity on germination probability and timing in P. thamnophila . Dry after-ripening and increased cool-storage duration consistently increased germination and shortened germination time, whereas storage temperature had comparatively weak effects. Germination probability increased from 45% in seeds planted directly from cool storage to 74% following dry after-ripening, and mean germination time was reduced by approximately 3 d. Seeds held in cool storage for longer durations germinated more rapidly and at higher percentages, indicating progressive dormancy release during storage. Maternal plant identity explained substantial variation in both germination probability and timing. Freezer storage resulted in only a marginal reduction in germination probability and did not affect germination timing, suggesting short-term freezing tolerance. P. thamnophila seeds exhibit physiological dormancy, retain viability for at least 210 d under short-term post-collection conditions and are likely tolerant of freezing. This study provides practical guidance for managing limited seed collections and conservation and recovery of P. thamnophila , as well as new, ecologically relevant information that increases our understanding of how this species is adapted to episodic rainfall in its habitat.