A Systematic Approach to Regeneration and Selection of Four Florist's Chrysanthemum (Chrysanthemum morifolium Ramat.) Cultivars with Different Susceptibility to Aphids

Florist's chrysanthemum is one of the most important flower crops in the global floricultural industry today. The susceptibility of many cultivars to a variety of pests, especially aphids, causes large economic loss. In this study, 29 chrysanthemum cultivars in our germplasm were evaluated on the susceptibility to aphids in the field. The cultivars were divided into 4 grades as: high resistant (HR), moderate resistant (MR), moderate susceptible (MS), and high susceptible (HS). The results showed that 12 cultivars were highly susceptible to aphids, and 2 cultivars were found with high aphids resistance. Four cultivars, including 'Ziyan Xinzhuang' with highest aphid susceptibility, 'Quanxiang Chongtian' and 'Bai Longzhao' with moderate susceptibility and moderate resistance, and 'Huanshui Mingzhu' with high resistance, were selected for in vitro adventitious shoot regeneration. The direct shoot regeneration rate under 16 media with different combinations of BA and NAA were studied by using leaf discs as explants. After 5 weeks' incubation, regenerated shoots were counted and analyzed. Significant differences in the requirements for BA and NAA were observed among cultivars 'Quanxiang Chongtian', 'Ziyan Xinzhuang', 'Bai Longzhao', 'Huanshui Mingzhu' with 73, 56, 27, 8% of explants generating shoots, respectively. The best regeneration frequency of 'Quanxiang Chongtian' was obtained at MS basal medium supplemented with BA 3.0 mg/L and NAA 0.2 mg/L, and of 'Ziyanxinzhuang' was with BA 2.0 mg/L and NAA 0.2 mg/L. By establishing the regeneration protocols for these chrysanthemum cultivars, further genetic study to improve aphid resistance can be well proceeded.