Biological control of Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker of kiwifruit, using endophytic bacteria recovered from a medicinal plant

Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of bacterial canker in kiwifruit (Actinidia deliciosa). Mānuka (Leptospermum scoparium) is a New Zealand medicinal shrub that produces essential oils with antimicrobial properties. The aim of this study was to determine whether endophytes from L. scoparium could be transferred to A. deliciosa and maintain their biocontrol activity. Five endophytic bacteria showed antagonism against Psa in vitro. The endophytic bacteria possessed multiple antibiotic producing genes, such as phenazine, 2,4-DAPG, and hydrogen cyanide, compounds that are known to inhibit growth of bacterial plant pathogens. Spontaneous chloramphenicol mutants and BOX-PCR fingerprinting were used to monitor endophytic colonization of antagonistic bacteria in planta. Three endophytic bacteria were transmissible to A. deliciosa by wound inoculation where they inhibited colonization by Psa and reduced disease severity in two different commercial cultivars.