Interspectific Hybridization Between Chrysanthemum Species And Research On Resistant Germplasm Innovation

Chrysanthemum(Chrysanthemum grandiflorum (Ramat.) Tzvel.) is one of the most important ornamentals, enjoying a major share of the cut flower and flowering pot plant market worldwide. However, the majority of chrysanthemum cultivars are susceptible to a range of diseases, pests and abiotic stresses. Many Chrysanthemum wild species have been recognized levels of tolerance to various biotic or abiotic stresses, and interspecific hybridization offers opportunities to transfer useful genetic variation to elite germplasm. Here, in order to introduce excellent traits from C. nankingense and C. makinoi to commercial cultivar Chrysanthemum grandiflorum'rm20-12', we produced F1 progeny between them. Then, to improve the ornamental value of F1 hybrid of C. makinoi x'rm20-12', we produced BC1F1 progeny using'rm20-12'as the recurrent parent. We surveyed the morphology, cold tolerance, aphid resistance and heat tolerance of these hybrid progeny. The main results and conclusion are listed as follows:(1) Ovary rescue was employed to create six interspecific hybrids from the cross between Chrysanthemum grandiflorum (Ramat.) Tzvel.'rm20-12'(2n=54) and its wild diploid relative C. nankingense (Nakai) Tzvel. (2n=18). The morphology of the hybrids differed from that of either parent. The leaf length and width of all three C. grandiflorum x C. nankingense hybrids exceeded that of the parents, as did the plant height of two and the inflorescence diameter of another of the hybrids. The RN1 plant was tall (66.88 cm), with long, wide leaves (6.18 cm and 3.99 cm, respectively). RN2 had the longest leaves (8.73 cm), widest leaves (5.62 cm) and largest inflorescence diameter (5.06 cm), while RN3 had a leaf length of 5.68 cm and a leaf width of 4.73 cm. One of the reciprocal hybrids NR2 was heterotic for leaf length and width (6.55 cm and 4.40 cm). All the hybrids bore yellow flowers. The cold tolerance of five hybrids was significantly superior to that of their C.×grandiflorum parent for the LT50S of the five hybrids lay between-15.93℃and-21.23℃, significantly lower than that of C. grandiflorum-14.33℃. C. nankingense appears to be a suitable donor to C. grandiflorum for cold tolerance. Interspecific hybridization clearly provides an effective means of cultivar improvement in chrysanthemum.(2) Three backcross hybrids using C. grandiflorum'rm20-12'as paternal parent was obtaine, and the morphology of them differed from that of both parents NR2 and'rm20-12' NR2R1 was tallest (64.55cm), and the inflorescence of NR2R3 developed most tubular florets, compared to their parents. The other characteristcs of hybrids were intermediate between two parents, or the same as one of the parents. The flower color in BC1F1 hybrids was orange and red, while NR2 bore yellow flowers and'rm20-12'bore red flowers. The cold tolerance of three BC1F1 hybrids was significantly superior to that of their C. grandiflorum parent for the LT50S of the three hybrids lay between-17.31℃and-19.06℃, significantly lower than that of C. grandiflorum-14.33℃. Backcross provides an effective means to improving ornamental value and cold torance of F1 hybrid.(3) The interspecific cross between Chrysanthemum grandiflorum (Ramat.) Tzvel. 'rm20-12'(R,2n=54) and C. makinoi Matsum.& Nakai (M,2n=18) was achieved using embryo rescue, and a single backcross progeny using C. grandiflorum 'rm20-12' as paternal parent was obtained. The morphology of the two independent F1 hybrids (RM1 and RM2) differed from that of both parents. RM1 had a larger inflorescence diameter (4.9cm) along with narrow leaves (2.2cm) and a reduced number of ray and tubular florets (17.5 and 144.5). RM2 was shorter (30.8cm) and its inflorescence developed fewer tubular florets (148.8) than either M or R. The BC1F1 hybrid was similar to its maternal plant RM2R in terms of leaf length and width, inflorescence diameter and the number of ray florets, while it produced fewer tubular florets (103.9) than either RM2 or R. The flower color in both F1 hybrids was red-purple (red-purple group N74A and N74B), while the BC1F1 plant bore red flowers (red group 55A). The aphid resistance and heat tolerance of RM1, RM2 and the BC1F1 hybrid were both significantly superior to that of C.×grandiflorum 'rm20-12'. Backcrossing can maximize the recovery of the elite traits. Interspecific hybridization followed by backcrossing shows clear potential for cultivar improvement in chrysanthemum.