First report of Botryosphaeria obtusa causing fruit rot of quince (Cydonia oblonga) in Spain

In autumn 2005, a severe fruit rot of quince (Cydonia oblonga) was investigated in commercial orchards in Córdoba province (southern Spain). Incidence of fruit rot (1-5%) was lower than that observed by farmers in previous years, which had more humid springs than in 2005. Affected fruits showed a soft rot that evolved rapidly covering the entire fruit surface and causing mummification (Fig. 1). A fungal stroma developed on the fruit surface but no spores, conidiomata or ascomata were observed. Some mummified fruits dropped prematurely, although most of them remained attached (Fig. 2). No symptoms were observed on leaves or branches of affected trees. The fungus consistently isolated from affected fruits was identified as Sphaeropsis malorum or Diplodia spp., the anamorph of Botryosphaeria obtusa, based on morphological characters (Phillips, 2006).

Detached fruits from healthy field trees of C. oblonga were cleaned with dry paper, surface sterilised with sodium hypochloride and inoculated by placing one drop (10 µl) of aqueous conidial suspension (2.5 x 10⁵ conidia per ml) on the peduncular area. All inoculated and control fruits were treated with one drop of water. The fruits were incubated in a growth chamber at 100 % RH and 23-24°C for 14 days, and then in another growth chamber at the same temperature and 40-50 % RH until fruit mummification. After 7 days, a firm and general rot starting in the peduncular area developed on all inoculated fruits but not on non-inoculated controls. Fruits rots and mummifications were similar to that observed in naturally infected trees in the field (Fig. 3). The anamorph of B. obtusa was reisolated from lesions of all infected fruits but not from control fruits.

B. obtusa has a worldwide distribution and affects numerous plant species. In fruit trees, it causes fruit rot, leaf spot and canker, but only the fruit rot phase was observed in our work. It has been cited as pathogen of C. oblonga in Canada, Greece, New Zealand, Australia, USA and South Africa (Farr et al., 2005), but to our knowledge, this is the first report of this pathogen causing fruit rot on quince in Spain.