Kiwifruit worldwide suffers from the devastating diseases of bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) and gray mold caused by Botrytis cinerea. Here, an endophytic bacterium XL17 isolated from a rape crown gall was screened out for its potent antagonistic activities against Psa and B. cinerea. Strain XL17 and its cell-free culture filtrate (CF) inhibited the growth of Psa and B. cinerea, Psa-associated leaf necrosis, and B. cinerea-associated kiwifruit necrosis. Electron microscopy showed that XL17 CF could damage the cell structures of Psa and B. cinerea. Genome-based taxonomy revealed that strain XL17 belongs to Pseudomonas bijieensis within the P. corrugata subgroup of the P. fluorescens species complex. Among the P. corrugata subgroup containing 31 genomospecies, the presence of the phl operon responsible for the biosynthesis of the phenolic polyketide 2,4-diacetylphloroglucinol (DAPG) and the absence of the lipopeptide/quorum sensing island can serve as the genetic marker for the determination of a plant-protection life style. HPLC detected DAPG in extracts from XL17 CF. MALDI-TOF-MS analysis revealed that strain XL17 produced cyclic lipopeptides of the viscosin family and orfamide family. Together, phenotypic, genomic, and metabolic analyses identified that P. bijieensis XL17 producing DAPG and cyclic lipopeptides can be used to control bacterial canker and gray mold pathogens of kiwifruit.

Over the last several decades, kiwifruit production has been severely damaged by the bacterial plant pathogen Pseudomonas syringae pv. actinidiae (Psa), resulting in severe economic losses worldwide. Currently, copper bactericides and antibiotics are the main tools used to control this bacterial disease. However, their use is becoming increasingly ineffective due to the emergence of antibiotic resistance. In addition, environmental issues and the changes in the composition of soil bacterial communities are also concerning when using these substances. Although biocontrol methods have shown promising antibacterial effects on Psa infection under in vitro conditions, the efficiency of antagonistic bacteria and fungi when deployed under field conditions remains unclear. Therefore, it is crucial to develop a phage-based biocontrol strategy for this bacterial pathogen. Due to the specificity of the target bacteria and for the benefit of the environment, bacteriophages (phages) have been widely regarded as promising biological agents to control plant, animal, and human bacterial diseases. An increasing number of studies focus on the use of phages for the control of plant diseases, including the kiwifruit bacterial canker. In this review, we first introduce the characteristics of the Psa-induced kiwifruit canker, followed by a description of the diversity and virulence of Psa strains. The main focus of the review is the description of recent advances in the isolation of Psa phages and their characterization, including morphology, host range, lytic activity, genome characterization, and lysis mechanism, but we also describe the biocontrol strategies together with potential challenges introduced by abiotic factors, such as high temperature, extreme pH, and UV irradiation in kiwifruit orchards. The information presented in this review highlights the potential role of phages in controlling Psa infection to ensure plant protection.