Effects of glandular trichomes on the development of Phytophthora infestans infection in potato (S-tuberosum)

S. berthaulltii Hawkes, a wild potato species, possesses two types of gland ular trichomes on its leaf surface: types A and B wich confer resistance to insects. Preliminary results indicated that the presence of glandular tric homes also confers resistance to Phytophthora infestans, the causal agent o f late blight. In this paper we report the evaluation of trichome character istics (density and exudate activities) performed on 8 lines of potato, inc luding the control varieties Desiree and Tropicana, 5 hybrid lines derived from intercrosses and backcrosses between S. tuberosum and S. berthaultii a nd one accession of S. berthaultii. Whole plants of the 8 genotypes were in oculated with a spore suspension of Phytophthora infestans in order to eval uate their resistance to late blight. The resultant disease incidence corre lated negatively with type A trichome density and with polyphenol-oxidase ( PPO) activity of type A trichome glands. The removal of type B trichomes ex udate by leaf dipping in ethanol did not influence the disease development after artificial inoculation of detached leaves. Type B trichome exudate wa s extracted and the fraction corresponding to Fatty Acids Sucrose Esters (F ASE) was recovered after Thin Layer Chromatography and tested on the fungal mycelium in vitro. The FASE exhibited a slight inhibitory effect on myceli um growth. The results of the experiments are discussed, and several hypoth eses regarding the possible role of types A and B trichomes are formulated.