Unexpected effects of chitinases on the peach-potato aphid (Myzus persicae Sulzer) when delivered via transgenic potato plants (Solanum tuberosum Linne) and in vitro

With the aim of producing insect-resistant potato plants, internode explants of Solanum tuberosum L. cv. Desiree were transformed with an Agrobacterium strain C58pMP90 containing an insect (Phaedon cochleariae: Coleoptera, Chrysomelidae) chitinase gene and the neomycin phosphotransferase (nptII) gene as selectable marker, both under the control of the viral CaMV 35S promoter. Three transformed potato lines (CH3, CH5 and CH25) exhibiting the highest chitinolytic activities were selected for feeding experiments with the peach-potato aphid, Myzus persicae (Sulzer), under controlled photoperiod and temperature conditions. Aphids fed on transgenic potato plants showed a reduced pre-reproductive period and an enhanced daily fecundity. Transgenic potato lines did not affect nymphal mortality, but improved several biological parameters related to aphid populations growth. Artificial diets were used to provide active (1, 10, 100 and 500 mug ml(-1)) and inactive (500 mug ml(-1)) bacterial (Serratia marcescens) chitinase to M. persicae. These compounds increased nymph survival at all active chitinase doses when compared to the control diet, while inactive chitinase did not. Although the pre-reproductive period was slightly shortened and the daily fecundity slightly higher, active and inactive chitinase provided as food led a reduction from 1 to 1.5 day populations doubling time. Therefore chitinase activity was responsible for the probiotic effects on aphids. Our results question the relevance of a chitinase-based strategy in the context of potato culture protection.