Diversity, phylogenetic identification, and pathogenicity of Lasiodiplodia species associated with branch dieback of sweet orange (Citrus sinensis) in Veracruz, Mexico

Background/Objective. Citrus branch dieback caused by species of the genus Lasiodiplodia constitutes an emerging disease that limits the productivity and longevity of sweet orange orchards (Citrus sinensis),because it causes gummosis, cankers, bark and wood necrosis, and branch dieback. Veracruz accounts for more than half of the national orange production; however, information on the etiological agents associated with this disease is limited. Therefore, the objective of this study was to determine the Lasiodiplodia species associated with sweet orange branch dieback in six municipalities of the northcentral region of Veracruz through multilocus phylogeny, confirm their pathogenicity, and compare theirvirulence. Materials and Methods. During the period from May to August 2023, 18 branches exhibiting dieback symptoms were collected from nine commercial sweet orange orchards distributed across six municipalities in north-central Veracruz, from which 36 fungal isolates were obtained. All isolates werepreliminarily identified by sequencing the ITS region, and of the 30 isolates assigned to the genus Lasiodiplodia, 12 representative isolates were selected for multilocus phylogenetic characterization considering the groupings obtained through ITS, cultural and morphological variability, as well as theirgeographical origin. Identification was performed through phylogenetic analyses of four loci (ITS, tef1-α, tub2, and rpb2) using Bayesian inference and maximum likelihood. The geographical distribution of the species was documented, and pathogenicity was verified on detached sweet orange branches by inoculating the 12 isolates, confirming the pathogenicity of the evaluated species. Results. Phylogenetic analyses allowed the identification of five Lasiodiplodia species: L. iraniensis (41.7%), L. pseudotheobromae (25%), L. subglobosa (16.7%), L. theobromae (8.3%), and L. mexicanensis (8.3%). L. iraniensis showed the widest geographical distribution, being detected in five of the six municipalities evaluated. All isolates were pathogenic and induced characteristic symptoms of the disease on detached branches, confirming the pathogenicity of the evaluated species. The comparison of virulence showed significant differences among species (p ≤ 0.05), with L. iraniensis inducing thelongest necrotic lesions, whereas L. mexicanensis and L. theobromae caused the shortest lesions. Conclusion. Sweet orange branch dieback in the north-central region of Veracruz is associated with a complex of Lasiodiplodia species with different geographical distributions and virulence. Five Lasiodiplodia species were identified, with geographical predominance of L. iraniensis (42%) and the longest necrotic lesions (>100 mm). The use of a multilocus phylogenetic approach allowed robust taxonomic delimitation of the species present and provides a basis for phytosanitary surveillance, thedevelopment of integrated management strategies, and future research on the epidemiology and diversity of Lasiodiplodia in citrus in Mexico.