Endophytic fungi from the common walnut and their in vitro antagonistic activity against Ophiognomonia leptostyla

Abstract

The common (or English) walnut (Juglans regia L.) is an economically important hardwood tree species cultivated worldwide for its edible nuts and high-quality wood. However, walnut trees are attacked by many pathogens causing economic damage. Among these pathogens, the most important fungal disease agent of walnut is Ophiognomonia leptostyla (Fr.) Sogonov (formerly Gnomonia leptostyla (Fr.) Ces. et de Not), which causes walnut anthracnose. In this study, endophytic fungi from various walnuts tissues (leaves, roots, twigs, shoots, fruits, and petioles) were isolated and molecularly identified by ITS gene sequencing. Additionally, the isolated fungi were tested for their in vitro antagonistic potential against O. leptostyla. A total of 35 endophytic fungi were isolated and species richness of endophytic fungi in roots was found to be higher than in aboveground organs. The most frequently isolated species was Fusarium sp. Seven isolates (Alternaria sp. CC-3, A. chlamydosporigena CC-8 and CC-9, Fusarium acuminatum CC-11, unidentified CC-16, Neonectria sp. CC-22 and unidentified CC-44) showed the antagonistic effects on O. leptostyla at different rates and the highest inhibition rate was obtained from Alternaria sp. CC-3 with 52.5%. Also, the presence of polyketide synthase I-II and non-ribosomal peptide synthase genes (possible antifungal-related genes) was investigated by PCR. From seven isolates showing antagonistic activity, PKS-I gene was detected in 3 isolates (Alternaria sp. CC-3, A. chlamydosporigena CC-8 and CC-9), PKS-II in one isolate (F. acuminatum CC-11), NRPS in two isolates (unidentified CC-16 and Neonectria sp. CC-22). None of three genes was detected in one isolate (unidentified CC-44). This is the first study to determine the antagonistic activity of the endophytic fungi isolated from walnuts against O. leptostyla. It is thought that the results will be beneficial in the future biological control programs for walnut anthracnose disease.