Apple (Malus domestica Borkh.) is widely cultivated in New Zealand, being a significant export crop. European canker (EC), caused by the fungal pathogen Neonectria ditissima, is the leading cause of apple trunk disease. It reduces the growth and yield of apple trees and may cause the death of the entire tree. In this study, culturable endophytes from apple shoots were investigated as a source of potential biocontrol agents to protect apple trees from N. ditissima infection.
Apple shoots without disease symptoms were taken from Lincoln University (Canterbury), Nelson and Hawke’s Bay orchards between 2015 and 2016 for endophyte isolation. A total of 1004 endophytic bacteria and 81 endophytic fungi (representing 33 fungal morphology groups) were screened for biocontrol activity against N. ditissima using dual culture assays. Eighteen bacterial and 18 fungal isolates inhibited radial growth of three N. ditissima isolates. Sixteen antagonistic bacteria were isolated from commercial varieties (Royal Gala, Braeburn and Jazz) in Integrated Fruit Production (IFP) managed orchards in all three regions and two from a heritage variety (Grimes Golden) from Hawke’s Bay Plant and Food Research orchard. Twelve antagonistic fungi were isolated from commercial varieties in IFP managed orchards across Nelson and six from organic orchards in Hawke’s Bay. The 18 bacteria and 15/18 fungi were from low EC infection blocks (infection rate ≤30%).
The isolates were identified using PCR sequencing, and potential pathogens eliminated from further studies leaving 16 bacterial and 15 fungal isolates. These bacterial isolates were identified as Bacillus and Pseudomonas species, and fungal isolates identified as Epicoccum, Chaetomium, Biscogniauxia, Neoseptophoma, and Penicillium species. Seven bacterial and 13 fungal isolates were positive for siderophore production assessed using chrome azurol S blue agar plates. This study indicated that endophytes isolated from apple tissues have the potential for use in sustainable control of N. ditissima.