Resurrecting a locally extinct species from Jordan : pre-germination treatments affect seed dormancy, germination dynamics and seedling survival in Rosa pulverulenta

Abstract

Habitat loss, fragmentation, and climate change present significant threats to global plant biodiversity. Small and isolated populations residing in threatened habitats at the edge of their natural distribution are particularly vulnerable to local extinction. Rosa pulverulenta M.Bieb., had its southernmost distribution in the Mediterranean basin in Jordan, but this remnant population recently extinct in the wild. Our goal to resurrect this species is hindered by the limited availability of seeds from the extinct population and a high degree of combinational dormancy in R. pulverulenta. To preserve as many genotypes as possible for eventual reintroduction, we aimed to identify the most effective seed treatment for breaking seed dormancy, and enhancing germination, and seedling establishment. Seeds were collected one season before extinction. We applied seven pre-germination treatments. The pre-treated seeds were then germinated at three temperature regimes (4/4 °C, 20/15 °C, and 25/20 °C), simulating winter and spring germination conditions. Warm-cold stratification, integral to all pre-treatments, proved effective in dormancy release, significantly enhancing germination. The highest germination (68 %) occurred at 4 °C, particularly in seeds treated with warm-cold stratification alone. Conversely, minimal germination was observed at higher temperatures (20/15 °C and 25/20 °C), suggesting potential induction of secondary dormancy. Furthermore, warm-cold stratification, especially when followed by microbial fertilizer, positively impacted seedling survival. Our study provides insights into effectively resurrecting the southernmost boundary of R. pulverulenta distribution in the Mediterranean basin, thereby preventing the global decline in the species' extent of occurrence. Strategically releasing seed dormancy and enhancing germination has important implications on scientific efforts reversing the declining trend of biodiversity in the Anthropocene. Additionally, seed collection from populations on the brink of extinction for resurrection is crucially required as the best method to preserve their genetic diversity. Therefore, this work offers a valuable framework that can be adapted to similar conservation efforts for other endangered plant species facing comparable threats. We emphasize the importance of further investigating how climate change can negatively affect seed dormancy, germination, and plant regeneration, ultimately leading to the local extinction of threatened populations.