Susceptibility of Pruning Wounds of Apple Trees to Diplodia mutila, D. seriata, Lasiodiplodia theobromae, and Neofusicoccum arbuti Infections and Conidial Release of Botryosphaeriaceae spp. in the Maule Region, Chile.

Abstract

Studies on the susceptibility of pruning wounds of different ages and the effect of pruning time on infection by Botryosphaeriaceae species in apple trees are scarce. This work aimed to determine the susceptibility of pruning wounds of different ages (1, 15, 30, or 45 days after pruning) and the effect of pruning time during early (June) and late pruning (August) in apple cultivars Fuji and Gala on the infection of Diplodia mutila, D. seriata, Neofusicoccum arbuti, and Lasiodiplodia theobromae. Additionally, seasonal conidial release of Botryosphaeriaceae spp. was monitored using Vaseline-coated glass slides in two orchards, cultivars Fuji and Gala, during two consecutive growing seasons (2020 and 2021) in the Maule Region, Central Chile. The analysis of the variance of each pruning wound age showed significant interaction between the factors, Botryosphaeria isolate × apple cultivar (P = 0.0001). The isolates of N. arbuti and D. seriata were significantly more aggressive than the other isolates of Botryosphaeria, with mean values of 45.2 mm (1 day of age) to 7.9 mm (45 days of age) and 31.0 mm (1 day of age) to 6.6 mm (45 days of age), respectively. Independent of the Botryosphaeriaceae species, the pruning wound susceptibility considerably decreased as the age of the pruning wound increased, where fresh pruning wounds (1 and 15 days) are more susceptible than older pruning wounds (30 and 45 days). Our results indicated significant (P < 0.0001) interaction between Botryosphaeria isolates and pruning time for both cultivars. Necrotic lesions varied among the Botryosphaeriaceae species, where lesion length was significantly greater in the isolates of N. arbuti, D. mutila, and D. seriata inoculated in early pruning than in inoculations conducted in late pruning. This study demonstrated a strong relationship between conidial release and rainfall, where 70.3 and 86.3% of the total conidia of Botryosphaeriaceae spp. were released during rainfall periods between June and August (winter). This work suggests that a delay in pruning times may be justified to reduce the risk of Botryosphaeria canker and dieback in apple trees in the Maule Region, Chile, considering rain-free days.