Abstract:

Green strawberry （Fragaria viridis） is a dominant species in some natural grasslands of Zhaosu County， where leaf spot disease occurs widely. To clarify the causal agents responsible for leaf spot disease on green strawberry and their biological characteristics， diseased leaf samples were collected from Zhaosu County， Xinjiang Uygur Autonomous Region， and subjected to fungal isolation and identification. The isolated fungi were identified based on morphological characteristics and multi-locus phylogenetic analyses. Results showed that three pathogenic fungi were obtained： Alternaria alternata， Colletotrichum tibetense， and Ascochyta nigripycnidia. Biological characterization revealed that all three fungi exhibited optimal mycelial growth at 25 ℃ and tolerated a broad pH range （4-11）， with the best growth occurring at pH 7-8， where colony diameters were significantly larger than under other pH conditions （P<0.05）. A. alternata grew best on corn meal agar， with soluble starch and peptone as the optimal carbon and nitrogen sources， respectively. A. nigripycnidia grew relatively slowly on all tested media， with potato-carrot agar supporting the most favorable growth； ammonium sulfate and soluble starch served as the most efficiently utilized nitrogen and carbon sources， respectively （P<0.05）. For C. tibetense， soluble starch and peptone were also the preferred carbon and nitrogen sources （P<0.05）， and its mycelium grew most rapidly on potato dextrose agar. All three pathogens exhibited robust mycelial growth under various light conditions. Pathogenicity assays confirmed that A. alternata， C. tibetense， and A. nigripycnidia are all causal agents of leaf spot disease on green strawberry. Among them， A. nigripycnidia was isolated most frequently （40.15%） and is thus considered the primary pathogen responsible for this disease.

Key words: Fragaria viridis, leaf spot disease, pathogen identification, biological characteristics