Pomegranate dieback caused by Lasiodiplodia gilanensis in California

Abstract

During the summer of 2009, decline of young pomegranate trees was observed in several orchards in the southern San Joaquin Valley of California. Symptoms were characterized by overall poor spring growth and dieback of one to multiple branches. Sunken lesions and cankers were observed on trunks and branches of diseased trees and cross sections revealed discoloration of the wood. A total of 25 symptomatic young trees (three to five year-old) cv. Wonderful were sampled from five different orchards in Riverside County in an attempt to determine the canker causal agent/s. Following isolation in culture medium, white fluffy and fast-growing fungal colonies that became light- to dark-green with age were isolated consistently from the margin between the discolored and healthy tissues. Morphological characters along with DNA sequence analyses of three gene regions, including the ITS1–5.8S–ITS2, and part of the β-tubulin, and translation elongation factor 1-α allowed the identification of the botryosphaeriaceous fungus Lasiodiplodia gilanensis. Koch’s postulates were completed in two year-old pomegranate trees cv. Wonderful under field conditions. Twelve months after inoculation, L. gilanensis isolates showed to be highly virulent producing lesions of up to 21 cm in length. This study reports for the first time the fungus L. gilanensis as a pathogen of pomegranate trees causing cankers and branch dieback.