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First Report of Diplodia seriata, the Anamorph of “Botryosphaeria” obtusa, Causing Fruit Rot of Olive in Spain

In October, 2006, 1,000 olive fruits (Olea europaea) were collected to study latent infections of Colletotrichum spp., causal agent of anthracnose, in an olive orchard in Córdoba Province (southern Spain). The fruits were incubated at 22 to 24°C and 100% relative humidity. Thirteen percent of the fruits showed a black rot that covered part or all of the fruit and pycnidia formed on the fruit surface. The fungus most consistently isolated from affected fruits was identified as Diplodia seriata, the anamorph of “Botryosphaeria” obtusa, by morphological criteria (1). Pathogenicity tests were performed on 50 immature and 50 mature fruits of olive cv. Hojiblanca. The fruits were washed in sterilized water with Tween 20 at 20 μl/liter and surface sterilized in 20% sodium hypochlorite for 2 min. Twenty-five of the immature and 25 mature fruits were wounded with a sterile 0.5-mm-diameter needle, inoculated by immersion in aqueous conidial suspensions (2.2 × 10⁵ conidia ml^--1) for 30 min. The same number of immature and mature fruits, wounded and unwounded, were treated only with sterilized Tween 20 water and served as the control. All fruit were incubated at 22 to 24°C and 100% relative humidity. The experiment was repeated twice. Eight days after inoculation, 75% of the mature inoculated fruits showed a general rot with pycnidia developing on the surface of the fruit. After 20 days, the first symptoms of disease were observed on immature olive fruits (2%) and all mature fruits. After 50 days, only 14% of immature inoculated fruits exhibited symptoms of the disease. The fungus caused mummification of mature fruits. D. seriata was reisolated from lesions on all infected fruits. There were no differences in the amount and severity of disease between wounded and unwounded fruits. Control fruits did not display disease symptoms after 50 days. Incidence of olive fruits affected by D. seriata in olive orchards in southern Spain is unknown, although it may be low since it was detected only in 1 of 12 olive orchards sampled for Colletotrichum spp. in 2006. Incidence of fruit rot associated with D. seriata in this orchard was 1.2% of fruits, which also were affected by Colletotrichum. D. seriata has a worldwide distribution and infects numerous fruit trees. In our research, D. seriata is pathogenic on olive fruits but weakly virulent. To our knowledge, this is the first report worldwide of the anamorph of “B.” obtusa causing fruit rot on olives.

Reference: (1) A. J. L. Phillips et al. Fungal Divers. 25:141, 2007.