Journal of Plant Pathology Archive

Abstract:

Walnut (Juglans regia L.) is widely planted in China. A new Fusarium wilt disease was observed in 5-yr-old walnut orchards in Hubei, China in mid-August of 2012 and 2013. The infected trees were found over an area of 50 ha. Yellowing and wilting of leaves, browned vascular tissues, and partially or entirely rotted roots were observed. A fungus was consistently isolated from symptomatic roots, forming dense, pale orange, aerial mycelium on Komada selective medium. Macroconidia were abundant (19.1 to 42.7 μm × 2.1 to 2.8 μm), curved to lunate, and three to four septate. Pathogenicity tests were carried out in greenhouse by injection of spore suspension (2 ml per plant of 107 spores/ml) into the rhizome of 5-yr-old plants of walnut cultivar 'Qingxiang'. Two months later, the inoculated plants started to yellow and wilt, similarly to those observed in the orchard, while the water-injected controls remained symptomless. The fungus was consistently re-isolated from inoculated plants but not from the controls. The isolate was identified as Fusarium sp. based on morphology (Leslie and Summerell, 2006). ITS and TEF-1α regions were PCR amplied using rDNA universal primers ITS1/ITS4 (White et al., 1990) and EF-728F/EF-986R (Carbone et al., 1999), respectively. The sequences of ITS (KP001165) and TEF-1α (KU559902) showed 99% to 100% identity to Fusarium solani (KJ019828 and KM044418.1). The pathogen was identified as F. solani based on its morphological and molecular characteristics. To our knowledge, this is the first report of Fusarium wilt on walnut trees caused by F. solani in central China.