Canker and wood rot pathogens present in young lemon orchards in south-west Arizona

Canker and wood rots are economically important preharvest diseases of lemons in south-western Arizona, where commercial lemon production is concentrated. However, the aetiology and epidemiology of canker and wood rots are not well understood. This study comprised a large survey of canker and wood rot incidence and severity in Arizona and the characterization of fungal species associated with the disease. A total of 5431 trees with ages ranging from 1 to 20 years old in 10 lemon orchards were surveyed from 2018 to 2020. Our survey results revealed that canker and wood rot occurred in all 10 lemon orchards studied. Canker and brown rots of twigs, branches, and trunks were the most prevalent symptoms of affected trees ranging from 1 to 20 years old. In contrast, canker and white rots of twigs and branches were observed mostly on 1- to 5-year-old trees. Disease incidence for both diseases was less than 2% on 1- and 2-year-old trees. Brown rot increased significantly in older trees, ranging from 62.9% to 100%. Fungi were isolated from canker and wood rot samples and identified based on morphological characters and DNA sequences. Fomitopsis meliae and Hypoxylon macrocarpum were the primary canker and wood rot pathogens isolated from the surveyed orchards, at frequencies of 89% and 11%, respectively. In pathogenicity tests, both fungi were capable of causing canker and wood rots on lemon cv. Lisbon branches and the necrotic length caused by F. meliae was twofold greater than that caused by H. macrocarpum.