Seasonal dynamics of Botryosphaeria dothidea infections and symptom development on apple fruits and shoots in China

Botryosphaeria dothidea is one of the most important pathogens of apple trees in China. It causes warts and cankers on shoots and fruit rot. In this study, multi-season experiments were conducted to investigate the seasonal dynamics of B. dothidea infection and symptom development on twigs and fruits of cv. Fuji through spraying and rain-splash inoculations. Fruit were most susceptible to infection from late May to mid-August. The length of the incubation period, i.e. from inoculation to the first lesion was observed, generally decreased with the age of fruit at the time of inoculation. Fruit inoculated in May-June developed visible symptoms from early August onwards, with a peak in early September. However, fruit inoculated in September developed visible symptoms within one week after inoculation. Twigs remained susceptible to infection by conidia from the initial extension stage in early May to late September. New extension shoots were most susceptible from June to mid-August and then became gradually less susceptible over time. When inoculated before the end of August, twigs developed visible lesions within the same season. In contrast, when inoculated late in the season, most lesions became visible during the subsequent season. The incubation period on twigs was shorter for inoculations conducted in June-August, with the shortest being 25 days. These results may contribute to the improvement of the management of this disease.