INTER-SPECIFIC HOST HYBRIDS AND PHALACRID BEETLES IMPLICATED IN THE LOCAL SURVIVAL OF SMUT PATHOGENS

In populations of the sedges Carex canescens and Carex mackenziei, the incidence and severity of a non-systemic floral smut fungus, Anthraco idea fischeri, was strongly associated with the occurrence of natural hybrids. Data from 23 localities showed that in the presence of the hy brid (13 localities), both parents sustained infection while in its ab sence (10 localities), both were disease-free. Furthermore, in mixed p opulations of parental and hybrid plants, the incidence and severity o f disease was always much greater on hybrid than parental plants (5 to 9 and 30 to 80-fold, respectively), and parental plants were more oft en diseased when growing close to hybrid plants. Hybrids were earlier regarded as completely sterile. however, we obtained successful germin ation of hybrid seeds from two localities. Thus we suggest that the hi gh disease occurrence on hybrid plants appears to reinforce an incompl ete fertility barrier that exists between the parents. The apparently precarious nature of this association at the individual population lev el (indicated by the almost total reliance of the smut on the hybrids for continued survival) is complicated by evidence indicating that inf ection of host plants by the fungus may result from either wind disper sal of basidiospores or through their transmission by the beetle Phala crus substriatus whose larvae feed on teliospores in the smut sori.