Taxonomic And Phylogenetic Studies Of Ascomycetes Associated With Common Woody Oil Crops In Sichuan Province

Sichuan Province,located in the southwestern region of China,possesses advantageous geographic and climatic conditions that support diverse ecological niches for the organism proliferation and evolution.Fungi have formed complex coevolutionary relationships with plants,acting both as saprophytes that decompose dead organic matter,promoting energy and nutrient cycling,and as pathogens causing plant diseases.Sichuan Province is one of the origins of woody oil crops,and recent national policy support has bolstered the economically important species such as olive,walnut,tung trees,and Sichuan pepper.These crops are vital for rual economic development and revitalization.Given the intergral role of fungi in mountain ecosystems,understanding their taxonomy ad pathogenicity is crucial for ensuring the high-quality and high-yield production of woody oil crops.In this study,samples were collected from 20 cooperatives and selfoperated planting areas in Chengdu,Leshan,Meishan,Mianyang,Guang’an,Guangyuan and Ya’an in Sichuan Province.Morphology and multi-gene phylogeny were incorporated to identify and classify the obtained fungal strains.Pathogenicity tests were conducted on the most common and widely distributed pathogenic fungi.The key findings are as follows:1.In this study,a total of 620 samples were collected from the dead branches and diseased leaves of woody oil crops,yielding 332 fungal isolates.Based on morphological and multi-gene phylogenetic analysis,these isolates were identified as 115 species,distributed in 53 genera,31 families,10 orders and 2 classes.Three new genera were described: Bicellulospora W.L.Li & Jian K.Liu,Neobrevicollum W.L.Li & Jian K.Liu,and Oleaginea W.L.Li & Jian K.Liu;53 new species and 61 new host records were introduced and reported respectly.Notely,Lophiostoma chiangraiense,Pseudochaetosphaeronema chiangraiense,P.magnoliae,and Seiridium rosarum were collected in China for the first time,Neokalmusia aquibrunnea was first discovered from a terrestrial habitat.This study also described the asexual stages of known species such as,Acrocalymma pterocarpi,Austropleospora ochracea and Loculosulcatispora hongheensis,and the sexual stages of Arthrinium jiangxiense,Diaporthe sackstonii,and Pestalotiopsis kenyana.2.The study incorporated extensive morphological and molecular data to update the phylogenetic trees of one suborder,22 families,and 12 genera.A revision of the family Pleurotremataceae was conducted,with Dyfrolomyces being synonymized under the earlier established genus Melomastia,resulting in eleven new combinations.3.Stable morphological characteristics are valuable for species identification among genera,whereas unstable features are unreliable for classification.In Melomastia,the morphology and texture of perithecial wall are easily affected by habitat and substrate,and unstable morphological characteristics.The number of septa in ascospores is not valuable for distinguishing between genera in Amphisphaeriaceae and Pleurotremataceae,but is important between species.In Heleiosa,the shape and size of gelatinous sheaths are key morphological criteria for species identification.The number of ascospores within an ascus is considered to be an important morphological feature at both genus and species levels.For example,Crassiparies is distinguished from other genera within the family based on the fact that it contains 4-spored asci.While in Cucurbitariaceae,the presence of 4 or 8 spores can be valuable for identification at the species level.4.In this study,the ITS gene region showed limited effectiveness in distinguishing species in Botryosphaeriaceae,Diatrypaceae,Diaporthaceae and Pestalotiopsis-like fungi.The tef1 gene was found as the ideal DNA barcode for Botryosphaeriaceae,while a combination of ITS,tef1,tub2,cal and his genes serve as best DNA barcodes to distinguish both intra-and interspecific differences within Diaporthe.The combination of tef1 and tub2 genes was effective for Pestalotiopsis-like fungi,but Diatrypaceae lacks suitable molecular markers for genus-level differentiation.Single-gene phylogenetic analysis confirmed tef1 as an ideal DNA marker for Melomastia.The rpb2 gene is recommended for species delimitation in Bambusicolaceae.For Nigrogranaceae,ITS and tef1 genes effectively differentiate species,while tef1 and rpb2 were significant in resolving interspecies relationships within the most genera of Lophiostomataceae.5.Based on Koch’s postulates,pathogenicity tests were conducted on 15 species of Botryosphaeriaceae.Among them,six species,namely Botryosphaeria dothidea,Diplodia acerigena,Di.mutila,Di.seriata,Dothiorella sarmentorum and Neofusicoccum parvum,exhibited high pathogenicity towards the branches and leaves of Olea europaea L.,Idesia polycarpa var.vestita Diels,Sapium sebiferum(L.)Roxb.and Acer truncatum Bung,and the pathogenicity showed differences between different species,between different strains of the same species,and the same species on different hosts.This study provides a comprehensive taxonomic investigation of pathogenic and saprobic fungi on woody oil crops in Sichuan Province.The acquisition of fresh specimens,fungal strains,and molecular data led to the description of several new genera and species.These finding contribute valuable data on fungal diversity in southwestern China and lay the groundwork for future studies on fungi-plant coevolution.By applying Koch’s postulates,the study identified pathogenic fungi causing diseases in woody oil crops,offering insights for disease management and cultivation of healthy,disease-free woody oil crops.