Abstract:

Genetic differentiation among three pine-stem rust fungi from China, i.e., Cronartium ribicola, C.flaccidum and C.quercuum, was assessed by random amplified polymorphic DNA(RAPD). Ten isolates(including an outgroup isolate)with different host and/or geographical origins were subjected to study. Pairwise similarity analysis was conducted on 51 RAPD loci detected by five selected primers. The result shown that although there were intraspecific variations, three rust pathogens were clearly separated as distinctive groups, thus justifying these traditional fungal taxa by using DNA data. Genetic relatedness between C.ribicola and C.flaccidum was closer than that between C.quercuum and either of the former two, this being consistent with the relationship reflected by disease symptom and telial-stage host range of these pathogens.High degree of intraspecific divergence was found between two C.flaccidum isolates which differ from each other in host specialization over their life circles, possibly demonstrating the genetic background underlying these two supposed formae speciales. Intraspecific variation was also found among C.quercuum isolates with different pine hosts, suggesting that the host specialization of C.quercuum in aceial stage as reported in Northern America may also exist in China. Evidences were also obtained that host adaptation, rather than geographic factors, is the primary force to drive genetic differentiation of the pine-stem rust fungi.

Key words: Pine-stem rust, Cronartium, Genetic differentiation, RAPD