Diversity of Lasiodiplodia species associated with canker and dieback in fruit trees from the Henan and Shandong provinces of China

Abstract

Lasiodiplodia is a widely distributed genus that is associated with a variety of diseases on many plant species, especially fruit trees. The current study conducted a disease survey of fruit trees growing in 12 orchards located within the Henan and Shandong provinces of China between 2020 and 2022. The symptoms observed included stem canker, branch dieback, and gummosis. Phylogenetic analyses of internal transcribed spacer (ITS), tub2, tef1, and rpb2 sequence data combined with morphological characteristics, revealed that the 19 isolates collected during the survey belonged to five documented Lasiodiplodia species, including Lasiodiplodia citricola, L. chiangraiensis, L. huangyanensis, L. pseudotheobromae, and L. theobromae, as well as two previously undescribed species, L. xinyangensis and L. ziziphi. In addition, the survey identified three novel host/pathogen interactions including L. chiangraiensis on loquat, L. citricola on apple, and L. huangyanensis on grapevine. Furthermore, the detailed phylogenic analysis indicated that four previously described Lasiodiplodia species were so closely related genetically that they would be better classified as synonyms rather than distinct species, so L. paraphysoides and L. nanpingensis should be considered synonyms of L. citricola, and that L. fujianensis should be a synonym of L. iraniensis, and L. henanica a synonym of L. huangyanensis. Pathogenicity tests confirmed that representative isolates of the two novel species and three new host/pathogen interactions identified in the current study were pathogenic to their original hosts, and fulfilled Koch’s postulates. Similarly, all of the isolates were found to be pathogenic on four alternative hosts, although a high degree of variation in virulence was observed.