Phylogeny, pathogenicity, and fungicide sensitivity of Botryosphaeriaceae fungi associated with Persian lime dieback in Sinaloa, Mexico

The occurrence of cankers on the trunk, gummosis, and dieback of branches and shoots in Persian lime trees has become a common disease in commercial orchards in Sinaloa, Mexico. This study aimed to identify the fungi associated with these symptoms, assess their virulence, and estimate their in vitro sensitivity to various fungicides. Symptomatic samples from Persian lime were collected from three commercial orchards, obtaining 30 fungal isolates belonging to the Botryosphaeriaceae family. Fungal identification of nine representative isolates was performed using a phylogenetic analysis based on DNA sequence data of the internal transcribed spacer (ITS) region and part of the translation elongation factor 1-alpha (tef1-alpha) gene. Sequence analyses were carried out using the Maximum Likelihood and Maximum Parsimony methods. The phylogenetic analysis revealed five species: Lasiodiplodia pseudotheobromae, L. subglobosa, L. brasiliense, L. iraniensis, and Barriopsis thailandica. The fungus L. pseudotheobromae was the most frequently isolated species (62.5 %). Pathogenicity tests on young Persian lime trees, using the mycelial plug inoculation method, demonstrated that all identified Lasiodiplodia species induced symptoms of necrosis and gummosis in branches. However, B. thailandica, found only as a saprophyte, did not cause symptoms. L. pseudotheobromae and L. iraniensis exhibited the highest virulence among the identified species. In vitro sensitivity tests showed effective concentration values inhibiting 50 % of mycelial growth (EC50) ranging from 0.0018 to 0.0162, 0.66-69.59, 56.72-299.21, and 0.332-13.766 mu g mL- 1 for the fungicides thiophanate-methyl, pyraclostrobin, pyrimethanil and chlorothalonil, respectively. This indicated that Lasiodiplodia spp. isolates were more sensitive to systemic fungicides thiophanate-methyl and pyraclostrobin, as well as the contact fungicide chlorothalonil.