Endophytic Microbial Communities in Lemon Trees and Relationship with Susceptibility to Xanthomonas axonopodis pv.citri

摘要

Citrus-producing countries are making efforts develop methods to control citrus canker, caused by Xanthomonas axonopodis pv. citri (Xac). Xac is a Gram negative rod that infects citrus leaves, stems and fruit through stomata and wounds. Communities of bacteria and fungi inhabit citrus plants as endophytes. Members of these endophyte communities may compete with pathogens and act as potential biological control agents. The objective of this study was to quantify and classify the bacterial endophytes in lemon leaves from an orchard with high (H) and low (L) areas of citrus canker incidence. Leaves from each area were collected, ground in buffer and processed on nutrient agar to isolate representatives of the endophytic bacteria community. Endophytes were isolated and identified by their 16S rDNA sequence. The endophytes were inoculated into leaves by syringe either alone and as co-inoculants with Xac. After inoculation with Xac, infection was measured as the number of canker pustules per leaf area. Bacterial counts were higher in samples from the H area yielding 45% Xac colonies, while in L area no Xac was detected. Nine non-Xac colony types were observed from the H plates while 18 colony types were detected from the L plates. In co-inoculation assays the citrus canker was sometimes reduced by coinoculation with the endophytes, but the effect was not significant.