Screening tomato varietal resistance against the two-spotted spider mite [Tetranychus urticae (Koch)]

Abstract

The two-spotted spider mite Tetranychus urticae (Koch) (Acari: Tetranychidae) is a serious pest of several crops, particularly tomato. Chemical control of the spider mite on this vegetable has not been very successful due to its rapid development of resistance to acaricides and insecticides. Tetranychus urticae performs differentially among tomato varieties. The aim of this study was to evaluate the plant features (the density of non-glandular and glandular trichomes) of seven tomato varieties and the survival, development, oviposition and life table parameters of T. urticae on each variety. In addition, the current study was intended to establish the relationships between damage caused by the mites and the mite population level on different tomato varieties. We used one variety, Beaufort, derived from a cross between the wild tomato Solanum habrochaites Knapp & Spooner and the cultivated tomato Solanum lycopersicum L., and six cultivated varieties: Beril, Bt-236, Impala, Simena, Troy and Y-67. The study revealed that when T. urticae fed on the Beaufort tomato variety, the demographic parameters [r(m) (0.121), R-o (5.79) and GRR (5.79)] were lower than when the mite fed on the other varieties. Additionally, the mite population level on the Beaufort variety was significantly lower compared with those on other tomato varieties. Moreover, the lowest mite survival rate was observed on the Beaufort variety. The densities of non-glandular (Type V) and glandular trichomes (Types IV, VI) on this variety were significantly higher than on the others. The variety's tolerance to mite damage was also found to be higher compared to other varieties. According to the life table parameters, population levels and rates of damage from T. urticae, the tomato variety Y-67 was found to be very susceptible to the mite. Also, the densities of non-glandular (Type V) and glandular (Type VI) trichomes in the susceptible variety were determined to be lower than in the Beaufort and some cultivated varieties. Variety Bt-236 was very similar to Beaufort in terms of the survival rates, damage rates and the density of Type VI glandular trichome on the leaf surface. The damage rate per female mite was highest on Y-67, intermediate on Simena, Troy and Beril, and lowest on the Beaufort, Impala and Bt-236 varieties.