Abstract: eranium sylvaticum plants differ in susceptibility to a macrocyclic rust, Uromyces geranii,depending upon whether they were previously infected by microcyclic rusts,Puccinia spp.and which rust(Puccinia morthieri or P. leveillei)previously diseased them. Field surrey, field transplantation and inoculation experiments show that previous infection by Puccinia spp. can decrease the susceptibility of G. sylvaticum to U. geranii. Furthermore,plants infected by P. morthieri show a lower probability of becoming infected by U. geranii compared to those infected by P. leveillei. Thus,interspecific pathogenic interactions and induced protective resistances are existed in G. sylvaticum populations. Induced protective resistance may be one important factor in explaining disease patterns observed in natural plant populations.

Key words: soil organic carbon, deep soil, revegetation, revegetation years, hilly Loess Plateau.