Aphids represent the most destructive of chrysanthemum pests to cultivation. Reliable variety sources of resistance and control methods are limited, so development of highly resistant breeding lines is desirable. An intergeneric hybrid between Dendranthema morifolium (chrysanthemum) variety 'Zhongshanjingui' and Artemisia vulgaris (mugwort) 'Variegata' was attempted. Most of the hybrid embryos aborted at an early developmental stage. Embryo rescue allowed the generation of hybrid plants, whose hybridity was confirmed by a combination of morphological, cytological and GISH analysis. The hybrids were vigorous, flowered normally, and their flower and leaf shape resembled those of the chrysanthemum more than those of the mugwort parent. The hybrids showed much higher resistance to chrysanthemum aphid (Macrosiphoniella sanbourni) than maternal chrysanthemum by inoculation test. The leaves of the hybrid developed a higher density of trichomes and secretory glands compared to the maternal chrysanthemum. GC-MS analysis revealed that approximately 51% of the essential oil in the hybrid leaves were monoterpenoids and sesquiterpenoids, while the proportion in the chrysanthemum was approximately 37%, and in the mugwort was approximately 90%. It is inferred that higher aphid resistance in the hybrid mainly owed to the leaf micromorphology and bioactive essential oil content.

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An intergeneric cross has been made between Dendranthema crassum (kitam.) kitam. (2n = 90; $) and Crossostephium chinense (L.) Makino (2n = 18; #). Most of the hybrid embryos aborted at an early developmental stage. Using ovule rescue, it was possible to establish a single intergeneric hybrid plant showing 2n = 54 chromosomes. The leaf length, leaf width and epidermal hair density of the hybrid were all intermediate between those of the parents. However the flower diameter, number of tubular florets, epidermal hair height and epidermal hair length exceeded those of both parents. A genomic in situ hybridization approach was able to distinguish between the parental genomes in the hybrid plant.Keywords Dendranthema crassum (kitam.) kitam. Á Fluorescent genomic in situ hybridization Á Crossostephium chinense (L.) Makino Á Intergeneric cross Á Anthemideae Á