Using bacterial endophytes from a New Zealand native medicinal plant for control of grapevine trunk diseases

Botryosphaeriaceous species are the causal agent of grapevine (Vitis vinifera) trunk diseases with very few options available for their control. They are also common endophytes in mānuka (Leptospermum scoparium), a New Zealand native medicinal plant, but there is no evidence of pathogenicity in this host. International research has demonstrated that endophytic bacteria can produce antimicrobial metabolites in planta. Thus, endophytic bacteria from mānuka may be viable options for biocontrol of botryosphaeriaceous species. This study was aimed at elucidating whether endophytic bacteria from mānuka with biocontrol activities can be transferred to grapevine as a heterologous host and express their bioactivity. Ten endophytic bacteria from a collection of 330 bacteria produced diffusible and volatile compound(s) that inhibited growth of six botryosphaeriaceous species. A combination of spontaneous rifampicin mutants and ERIC PCR was used to confirm endophytic colonization of the introduced antagonistic bacteria in planta. The results showed that two isolates, Pseudomonas sp. I2R21 and Pseudomonas sp. W1R33, were transferable from mānuka to grapevine when inoculated onto wounds, where they inhibited colonization by two botryosphaeriaceous species, Neofusicoccum luteum and N. parvum, respectively. The endophytic bacteria reduced lesion length caused by the pathogens (32-52%) compared to untreated controls. This study indicated that mānuka can provide a new source of microorganisms for use in sustainable agriculture.