Non-host specificity of Botryosphaeriaceae on macadamia and blueberry

The ability of species in the Botryosphaeriaceae to inhabit seemingly healthy plants, reside as endophytes yet result in serious disease under stressful environmental conditions is poorly understood, as is their ability to colonise many unrelated hosts often without causing disease. Although many species of Botryosphaeriaceae have a wide host range, there is dearth of information on pathogenic variation of isolates of the same species on different hosts. In this study we used 16 isolates belonging to two genera of Botryosphaeriaceae from seven host plant species, to test the hypothesis that there are significant differences in pathogenic variation, varietal preferences and cross-pathogenicity in Botryosphaeriaceae on two unrelated host crops (macadamia and blueberry). Using the detached leaf and stem inoculation assays, we observed significantly (P < 0.05) high levels of pathogenic variation among isolates of Neofusicoccum parvum and compared with three other Neofusicoccum spp. and the three Lasiodiplodia spp. Host specificity was not observed among the isolates, as all were pathogenic on both hosts, but the aggressiveness of the isolates varied on the hosts, regardless of the source of the isolates. Between the host plants, blueberry was significantly more susceptible, regardless of the isolates than macadamia. There were significant (P < 0.03) differences among the four macadamia cultivars, isolates and cultivar × isolate interaction. Similar results for pathogenicity, aggressiveness and pathogenic variations were obtained using both the detached leaf and stem inoculation assays. Implications of these findings for disease management in cropping systems are discussed.