Using Burkholderia sp. as a biocontrol agent in kiwifruit plants against Neofusicoccum parvum

Abstract

Actinidia chinensis (kiwifruit) is an important horticultural crop in New Zealand. A fungal pathogen, Neofusicoccum parvum (teleomorph Botryosphaeria), was found causing fruit drop symptoms in kiwifruit orchards. To target this issue, a potential bacterial biocontrol agent, Burkholderia sp. (isolate W4R11), was used to test its efficacy against N. parvum in planta. Molecular approaches and in vitro testing were conducted prior to the glasshouse trial to provide insights on understanding the biology of N. parvum and Burkholderia sp. This work demonstrated the in vitro antagonist effect of Burkholderia sp. against N. parvum. Cultural practices on the two organisms were also conducted in the laboratory, providing inoculant material for the in planta testing. This is the first study testing the use of Burkholderia sp. (isolate W4R11) as a wound protectant in one-year old kiwifruit plants against N. parvum. It demonstrated an apparent competition between the two organisms and provided suggestions on colonization and movement of Burkholderia sp. and N. parvum in kiwifruit plants. The Burkholderia strain can colonise 15 -30% of the plants, which had no substantial differences compared to N. parvum. When examining the stems further from the wound site, Burkholderia sp. showed suppression on N. parvum, resulting in a non-fungal colonization. The result suggested: (1) Burkholderia sp. may have a better colonization ability and faster movement than N. parvum in kiwifruit plants; (2) Burkholderia sp. can be used as a wound protectant after pruning or harvesting of the kiwifruit to inhibit wound-invading pathogens; and (3) to prune the kiwifruit stem 20 cm from the infected site and then applying the biocontrol agent may reduce disease incidence in planta. Future studies should utilize more replicates and field testing to confirm the biocontrol ability of this particular strain.