Identification, Distribution, and Pathogenicity of Diatrypaceae and Botryosphaeriaceae Associated with Citrus Branch Canker in the Southern California Desert.

Abstract

Several members of the families Botryosphaeriaceae and Diatrypaceae are known as canker and dieback pathogens of a number of woody hosts. Because desert citrus production in California can occur in proximity to table grape production, it was suspected that fungi associated with grapevine cankers might also be associated with citrus branch canker and dieback decline. To determine the fungi associated with branch canker and dieback disease of citrus in the southern California desert regions, surveys were conducted from 2011 to 2013 in the major citrus-growing regions of Riverside, Imperial, and San Diego Counties. Cankered tissues were collected from branches showing symptoms typical of branch canker and dieback. Various fungal species were recovered from necrotic tissues and species were identified morphologically and by phylogenetic comparison of partial sequences of the internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2), β-tubulin gene, and elongation factor 1-α genes with those of other species in GenBank. Four fungi, including Neoscytalidium hyalinum, Eutypella citricola, E. microtheca, and an unnamed Eutypella sp., were associated with branch canker. N. hyalinum was the most frequently recovered fungus from symptomatic tissues (31%) followed by E. citricola (10%), E. microtheca (4%), and the Eutypella sp. (2%). In pathogenicity tests, all fungi caused lesions when inoculated on 'Lisbon' lemon (citrus) branches. Lesions caused by the Eutypella sp. were significantly longer than those of the other Eutypella spp.; however, they did not differ significantly from those produced by N. hyalinum. The most-parsimonious unrooted trees based on the combined data of ITS and partial β-tubulin gene region sequences showed three distinct clades of Eutypella spp. (E. citricola, E. microtheca, and an unidentified Eutypella sp.). Similarly, ITS and partial translation elongation factor 1-α gene region sequences differentiated two species of Neoscytalidium, N. hyalinum and N. novaehollandiae. Identifying the diversity, distribution, and occurrence of these fungal pathogens is useful for the management of citrus branch canker and dieback disease in the desert citrus-growing regions of California.