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Botryosphaeria dothidea is a fungal pathogen causing canker, dieback, and fruit rot of apple trees worldwide. Ascospores are an important source of inoculum of Botryosphaeria canker in China. Experiments were conducted under both controlled and natural conditions to study perithecium formation in relation to environmental conditions. Perithecia of B. dothidea were detected on cankered lesions throughout the apple growing season except in July and in some years including August under natural conditions. On newly formed canker lesions, the first perithecium was detected as early as August, about 1 week after rainfall. Perithecia matured successively, lasting from early August to June of the next year, with a peak in late September or early October. Temperature and rainfall are two key environmental factors affecting perithecium formation. Under controlled conditions, perithecia were produced only on cankered shoots incubated at test temperatures of 20 and 25°C and wetted by >3 days of simulated rainfall per week. The number of perithecia produced on canker lesions increased with the increase in rainfall duration. Perithecia were formed on canker shoots exposed to rainfall only in June, July, and August but not in September. Rainfall of >3 days per week can be used to predict the initial formation of perithecia in the main apple production areas in China to assist disease management. [ABSTRACT FROM AUTHOR]

Fungal pathogens use plant surface physiochemical signals to trigger specific developmental processes. To assess the role of phospholipase C (PLC) in mediating plant stimuli sensing of Alternaria alternata , the function of three PLC genes was characterized by constructing Δ AaPLC mutants. Here we showed that fruit wax-coated surfaces significantly induced appressorium formation in A. alternata and mutants. Germination of Δ AaPLC mutants did not differ from the wild type. Deletion of AaPLC1 led to the decrease of appressorium formation and infected hyphae, but the degree of reduction varies between the different types of waxes, with the strongest response to pear wax. Appressorium formation and infected hyphae of the Δ AaPLC1 mutant on dewaxed onion epidermis mounted with pear wax (θ4) were reduced by 14.5 and 65.7% after 8 h incubation, while Δ AaPLC2 and Δ AaPLC3 formed the same infection hyphae as wild type. In addition, AaPLC1 mutation caused pleiotropic effects on fungal biological function, including growth deficiency, changes in stress tolerance, weakening of pathogenicity to the host, as well as destruction of mycotoxin synthesis. Both AaPLC2 and AaPLC3 genes were found to have some effects on stress response and mycotoxin production. Taken together, AaPLC genes differentially regulate the growth, stress response, pathogenicity, and secondary metabolism of A. alternata .