Responses of seed germination to low temperature storage in different cultivars of Xanthoceras sorbifolium

To study the seed dormancy and germination mechanism of Xanthoceras sorbifolium, the seeds of four cultivars [‘Putong’(PT),‘Qihong’(QH), ‘Wofeng’(WF) and‘Woshi’(WS)] were stored at -20 ℃ for different periods (30, 60, 90, 120, 150 d). The seed germination indexes were determined in each treatment, and the changes of reserve substance and hormone content were also analyzed in three stages including before storage, after storage, and 7 days of germination. The results were as follows: (1) Cold storage could significantly promote the germination rate and germination potential of small seeds (PT, QH). The best treatment was cold storage for 60 d, and the germination rate was up to 48.3% and 58.3%, respectively. The effects of cold storage on large seeds (WF and WS) was lower than that of small seeds. (2) The kernel oil content, seed shell thickness (SST) in four cultivar seeds all decreased significantly during periods of cold storage and germination, especially in 3-7 days of germination, the oil content and SST (except WS cultivar) decreased notably. However, water content in kernels increased rapidly within 1-3 days of germination and then slowly increased to the peak value on the 7th day. The contents of soluble sugar in kernels increased significantly at the 3-4 days of germination. (3) Cold storage increased GA/ABA and tHor/ABA ratios in small seeds (PT, QH), promoted oil degradation, made seed shell thinning and break seed dormancy. In conclusion, the main factors leading to dormancy in X. sorbifolium seeds are larger in size, higher shell thickness and more hardness, physiological post-ripening, and belongs to comprehensive dormancy type. Cold storage at -20 ℃ for 60 d can improve the germination rate of PT, QH and WF seeds, reduces dormancy degree, while the cold storage time of WS seeds needs prolonging to 150 d. The method using -20 ℃ storage with wet sand germination is a rapid and simple method to promote X. sorbifolium seeds germination. This study provides a reference for the promotion of superior varieties and the research on the seed breaking dormancy mechanism in X. sorbifolium.