Effect of ultra-dry storage on Stylosanthes seed and its genetic stability

Abstract: Stylosanthes spp. originated in central and South America, consisting of 44 species and subspecies, in a promising tropical legume forage. It is planted in one-third of the tropical and south subtropical area of the world in terms of variety. It mainly regenerates in the form of a seed, and it is planted and used in southern China. The seed is the conservation of germplasm, breeding, and material basis, and it is important material for physiological studies. This study goes into the development of the tropical pasture seed ultra-dry conservation, breeding, and germplasm resources for biodiversity conservation and utilization of great significance.The ultra-dried seed storage technique is energy efficient, effective, and easy to manipulate for seed storing. While most tropical crop seeds do not have dehydration tolerance, the ultra-dried storage technique is a constraint in these seeds. However, our previous study showed that the Stylosanthes guianensis seed has very high tolerance to ultra-dried storage. The ultra-dried seeds of S. guianensis with a moisture content of 3.17% has high tolerance to aging after treatment at 50℃ for 15 days. These results show that ultra-dried treatment could increase the seeds storability of S. guianensis. The most suitable moisture content is 3%±0.2 for long-term ultra-dried storing.Ultra-dry treatment can improve storage stability. However, this does not mean that the lower the moisture content the better. Researches proved that when the moisture content lowered to a certain extent, the vitality of the seed dropped. Too much ultra-dry treatment does not have a positive effect on the seed longevity. In fact, it may even decrease it. The ultimate aim of seed storage is to preserve the innate hereditary feature and pass it without variation by harmful influences. When storing seeds, not only should the seeds' high germinating ability be preserved, but genetic stability should also be kept. Therefore, the detection of the genetic stability of the storage seed was very important in evaluating the storage effects. Morphologic features, cytological markers, physiologic and biochemical indexes, and molecular researches could be applied in the study of the changes in genetic integrity.The purpose of this study was to dertmine the effects of ultra-dried seed storage for ten years through analyzing the seed germination, viability, phenology, morphological characteristics, agronomic traits, and genetic stability of Stylosanthes guianensis cv. Reyan No. 5 compared to the methods of -20℃ and room temperature storage. With three seed storing methods for 10 years, a seed with moisture of 3.17% at ultra-dry storing, a seed with moisture of 8.7% at -20℃ storing, and a seed with moisture of 8.7% at room temperature storing have a germination potential of 77.9%, 71.3%, and 18.5%, respectively and a vitality index of 60.10, 50.79, and 4.98, respectively. Both germination potential and vitality index have significant differences between an ultra-dry seed and a seed with moisture of 8.7% at -20℃ storage for 10 years. There are very significant differences between a seed with moisture of 8.7% at room temperature storage and a seed in ultra-dry storage or a seed stored at -20℃ for 10 years. The ultra-dry long-term storage for Stylosanthes seeds is the best method among them. An investigation on the Stylosanthes morphologic characteristics and its AFLP molecular analysis showed that the ultra-dry seed storage does not cause plant morphological phenotypes to change or AFLP molecular genetic variation. The ultra-dry storage seed of Stylosanthes can greatly reduce the energy in long term storing with characteristics of being simple, effective, and widely applicable. This result will be useful in the field of Stylosanthes germplasm conservation and breeding.