Biocontrol potential of antagonistic fungal endophytes against Neonectria ditissima on apple

Abstract

The efficacy of 311 fungal endophytes isolated from the stem and leaf tissues of apple against Neonectria ditissima, the causal pathogen of apple European canker, was evaluated using in vitro and in planta antagonistic assays. The bioactivity of 37 isolates that showed the highest antifungal activity in the dual-culture assay were evaluated further using other in vitro antagonistic assays, volatile, culture filtrate, siderophore, and enzyme activity assays. Following these, in planta assays were conducted to determine the colonisation ability and pathogenicity of the selected endophytes on apple tissues. Of the 37 isolates, 10 were shown to be pathogenic on apple shoots while 11 showed disease symptoms on wounded fruit. When twenty-seven isolates were evaluated for their endophytic colonization capability, 25 were recovered from the stem tissue, up to 5 cm below and above the inoculation point. Based on the results of their pathogenicity, in vitro antagonism, spore production ability, and relative length of stem tissue colonised, four isolates (Biscogniauxia sp., Neosetophoma sp., Paraphaeosphaeria sp. and Trichoderma sp.) were selected and tested in a detached shoot assay to assess their ability to reduce infection by N. ditissima. The results of the in planta biocontrol assay indicated that two endophyte isolates (Paraphaeosphaeria sp. FE9 and Trichoderma sp. FE3) reduced the colonisation of N. ditissima in the apple tissues and have the potential for use in the sustainable control of N. ditissima. Further work will be carried out this season to evaluate their efficacy to reduce infection in attached apple shoot tissue.