Effect of plant variety, plant age and photoperiod on glandular pubescenceand host-plant resistance to potato moth (Phthorimaea operculella) in Lycopersicon spp.

The effect of plant age and daylength on glandular pubescence was determine d for two lines of tomato derived from Lycopersicon hirsutum (BTN 979 and L A 1777A) and a variety of L. esculentum (N 91-1-1-1-1). Densities of type I , IV, VI and VII glandular trichomes were lowest in N 91-1-1-1-1 and, over all varieties, were more dense on plants aged greater than 6 wk. Daylength interacted with variety to significantly affect densities of type VII trich omes only. Host-plant resistance to Phthorimaea operculella was determined in preliminary tests using insects cultured from founders from a potato cro p and in confirmatory tests using (less readily available) insects recovere d from foliage of a tomato crop. Mortality of ex-potato neonates on LA 1777 A and BTN 979 foliage was higher 18 h after placement than for N 91-1-1-1- 1, with no effect of day length or plant age. Mortality for ex-tomato neona tes followed a similar trend. Ten days later, two-thirds of ex-tomato larva e had established mines on N 91-1-1-1-1 but fewer (16.7 %) were live on oth er varieties. Stepwise multiple regression using variety as the sole factor was significant (P < 0.001) in accounting for 61.4% of the variation in ex tomato larval survival but addition of other factors to the regression mode l was not significant. BTN 979 supported fewer, smaller adults to develop t han did N 91-1-1-1-1, whilst no adults developed on LA 1777 A. In a non-cho ice test using ex-potato adults, significantly more eggs were laid on N 91- 1-1-1-1 than on L. hirsutum varieties and 9-wk-old plants were preferred ov er plants three weeks older or younger. The same variety and plant age tren ds were evident in a free-choice test using ex-tomato adults.