Effects of the Harvest Method on the Infestation of Chestnuts (Castanea sativa) by Insects and Moulds

Chestnuts were collected either every 7 days from suspended nets used to intercept the fruits, every 2 days from the ground or every 7 days from the ground. Nuts were visually inspected after collection for the presence of exit holes of the chestnut weevil (Curculio elephas) and the chestnut moth (Cydia splendana), and 20 nuts per sampling and tree were bisected to assess fungal colonization. Apparently healthy nuts were incubated at 24 C and 70–80% relative humidity for 21 days. All nuts were bisected after incubation and examined for the presence of insects and moulds. The harvest method did not have a statistically significant effect on either moulding or insect infestation except on Amphiporthe castanea. This vertically transmitted fungal endophyte was less frequently isolated from fruits collected after 7 days from the ground. The black rot fungus Ciboria batschiana did not occur in chestnuts intercepted in nets, but the difference to chestnuts collected from the ground was statistically not significant. The frequency of nuts colonized by C. batschiana was low in general probably due to the hot and dry summer in 2003. Big, marketable fruits appeared to be less frequently colonized by insects and moulds right after collection. This difference disappeared after incubation except for the chestnut moth. The mother tree had the greatest effect on fungal and insect infestation, indicating the importance of the genetic disposition and/or the phytosanitary situation of each tree. The chestnut weevil preferred chestnuts of the variety Lüina to those of the variety Torcion , whereas the fungi A. castanea, Trichothecium roseum, Clonostachys rosea and Penicillium spp. preferentially colonized chestnuts of the variety Torcion . Introduction Chestnuts are typical seasonal fruits that maintain their optimal commercial quality, turgescence and health for only a comparatively brief period. One of the major difficulties is the high perishability of the product. The major factors in postharvest depreciation are moulding or rotting caused by fungi and the larval development of insects (Wells and Payne, 1980; Breisch, 1993; Bassi et al., 2001). Insect damage is usually due to infestations of the chestnut moth Cydia splendana and the chestnut weevil Curculio elephas, which attack the fruits while still on the trees. Damage increases concomitantly with the development of the larvae (Giacalone and Bounous, 1993). Fungal infections often start in the larval galleries of insects (Wells and Payne, 1980), and many nuts become infected on the ground before picking. Some moulds are considered endophytes that colonize the fruits at various stages during their development but do not cause any symptoms of disease until after fruit fall (Washington et al., 1997, 1998). Expansion of fungal mycelia in the fruits and degradation of the cotyledons occur mainly during storage (Rutter et al., 1990; Giacalone and Bounous, 1993). At early infection stages, it is not easy to differentiate slightly mouldy or parasitized nuts from the good ones until they are processed or consumed (Rutter et al., 1990). As a consequence, various nut-treatment techniques have been developed. The most common are hydrotherapy (cold bath) and thermo-hydrotherapy (warm bath), which was developed in Italy during the 1930s. Thermo-hydrotherapy is nowadays the standard method used for its proven ability to control insect infestations without influencing nut quality (Jermini et al., 2006). Similarly, hydrotherapy prior to cold storage reduced moulding significantly from 60% to 30% (Delatour, 1978; Jermini et al., 2006). However, a disease incidence of one-third of mouldy nuts is still high, and further control strategies are needed for commercial chestnut production. In areas with traditional subsistence chestnut culture www.blackwell-synergy.com J. Phytopathology 155, 497–504 (2007) 2007 The Authors Journal compilation 2007 Blackwell Verlag, Berlin doi: 10.1111/j.1439-0434.2007.01269.x