Advances in research on distant hybridization of chrysanthemum.

Chrysanthemum is one of the most important ornamentals in the world,whereas most of chrysanthemum cultivars have a weak resistance to diseases,pests and other environmental stresses,thus their quantities and qualities are seriously restricted.As a result,it is very necessary to improve chrysanthemum’s resistance.By far,distant(interspecific and intergeneric) hybridization has become a promising approach to improve chrysanthemum’s tolerance through introducing tolerant traits from some wild species in Chrysanthemum and related genera into it.However,various barriers often exist in chrysanthemum distant hybridization and severely influence the utilization of these excellent germplasm resources.Therefore,this paper presents a detailed review on the information of many wild species in Chrysanthemum and its closely related genera,the types of incongruity barriers during chrysanthemum distant hybridization,the means of overcoming incongruity barriers,and the methods of hybrid identification as well.In addition,the prospects of chrysanthemum distant hybridization are put forward.Taken together,the general aim of this review is to provide valuable knowledge for the improvement of chrysanthemum cultivars in the near future.