Verification of aecial host ranges of four Gymnosporangium species based on artificial inoculation.

Aecial host ranges of four Gymnosporangium species causing cedar-apple rust diseases, G. asiaticum, G. cornutum, 5. japonicum and G. yamadae, were investigated through artificial inoculation. Thirteen species of nine genera among Rosaceous plants, which have been reported as social hosts in Korea, were inoculated with fresh teliospores spores in early days of May of 2000 and of 2001, respectively. In the results, we re-confirmed that there was highly specific relationship between the rust species and aecial hosts and report new aecial hosts of four Gymnosporangium species. Teliospores of G. cornutum collected from Juniperus rigida successively produced spermogonia and aecia only on Sorbus alntifolia, the first report on host alteration of G. cornutum in Korea. Positive responses by teliospores of G. japonicum from J. chinenis of Suwon and from J. chinenis var. horizontalis of Jeju island were obtained only on P. villosa. Crataegus pinnatifida was confirmed as a new aecial host of G. viatium. Until this time, G. ymadae was believed to have Malus as the aecial host. However, teliospores of G. yamadae collected from J. chinensis var. kaizuka successively formed spermogonia and aecia on the leaves of Chaenomeles lagenaria, C. sinensis, Pyrus pyrtifolia var, culta, P. ussuriensis, Malus pumila and M. sileboldii. The date for maturation of spermogonia and aecia, and symptom development varied according to the rust fungi and aecial host plants, respectively.