Effect of Snail (Helix aspersa) Damage on Botrytis Gray Mold Caused byBotrytis cinereain Kiwifruit

Abstract

In three (1994) and two (1995) kiwifruit vineyards in the coastal area of California (San Luis Obispo County), the incidence of fruit with all sepals removed by the common brown garden snail (Helix aspersa) ranged from 11 to 35% in 1994 and 2 to 15% in 1995. Partially damaged fruit with fewer than three sepals per fruit ranged from 7 to 20% in 1994 and 3 to 5% in 1995. Swollen tissues associated with healing developed around the receptacle (stem end) from which sepals had been removed by snails. In a 3-year study, kiwifruit with and without characteristic damage (full removal of sepals) by snails were harvested from two vineyards and stored in controlled-atmosphere (CA) cold (-0.5°C) storage. After 3- to 5-month storage, fruit with snail damage consistently had more Botrytis gray mold than fruit not damaged by snails (P < 0.01). In separate studies, kiwifruit caged with snails developed more gray mold than fruit caged without snails after 3 to 5 months in CA storage in 1994 but not in 1993. In two vineyards, removal of sepals by hand did not consistently increase gray mold in CA storage. More viable propagules of Botrytis cinerea and other mycoflora were recovered from fruit that had snail slime than fruit without slime (P < 0.05). Although snail slime did not affect the germination of B. cinerea conidia on a nutrient-rich medium (acidified potato-dextrose agar), snail slime increased germination of B. cinerea conidia on a nutrient-poor medium (acidified water agarose) to more than 50% compared with 1 to 2% germination without slime after incubation at 21°C for 22 h. These results suggest that wounds caused by snails eating the sepals around the receptacle area of kiwifruit and (or) stimulation of conidial germination by snail slime may lead to more infections by B. cinerea.