Interaction between <i>Botryosphaeria dothidea</i> and <i>Neofusicoccum parvum</i> Causing Cankers in Almond and Effect of Wood Age on Infection

Botryosphaeriaceae fungi are the main pathogens associated with almond decline syndrome in southern Spain, with Botryosphaeria dothidea and Neofusicoccum parvum being the most frequent and aggressive species, respectively. They can occur singly or coinfect trees, with the disease severity being usually higher in younger than in older trees. In this study, coinoculations of B. dothidea and N. parvum with adjusted conidial suspensions were conducted at different timings in detached shoots and potted plants, using green (1-year-old) or lignified (2-3-year-old) tissues of cv. Avijor to determine the effect of coinfections and wood age on the disease development. Cankers developed on lignified tissues were significantly smaller than on green tissues. There were no significant differences in aggressiveness among treatments in lignified tissues; whereas B. dothidea and N. parvum were significantly more aggressive in green tissues when inoculated individually, or when N. parvum was inoculated four days before B. dothidea. The biomass of each pathogen was quantified by multiplex qPCR in the margin and 2 cm beyond the margin of necrotic lesions in green tissues. The highest relative inoculum density was found in plants inoculated with B. dothidea, N. parvum, co-inoculated simultaneously, or in those where B. dothidea was inoculated 4 days before N. parvum. Although at a much lower density, both pathogens were detected in asymptomatic tissues 2 cm beyond the necrotic lesions. These findings suggest that interactions during coinfections alter the relative abundance and aggressiveness of these pathogens, with disease development being strongly influenced by the age of the host tissue.