VARIETAL RESISTANCE OF NINE POTATO VARIETIES TO NATURAL INFESTATION BY CERTAIN LEAF PESTS AT GEMMEZA REGION, EGYPT,

The varietal resistance of the nine potato varieties Lesita, Nicola, Diamont, Baraka, Draga, Spunta, Serrina, Mondial and Timate to natural infestation with seven serious pests attacking leaves during the two suc­cessive years, 1991 and 1992 was studied at Gemmeza region. The re­sults showed that in summer plantation in both 1991 and 1992 sea­sons, Lesita var. seemed to be more susceptible to Aphis gossypii Glover , whereas Spunta var. in the first season and Baraka var. in the second showed the highest levels of resistance_ Lesita potato plants were more attractive to A. craccivora Koch than the other tested varieties . Serrina Var. was less preferrable to insect attack. Spunta var.in the first year and Serrina var. in the second showed the highest level of resistance to Myzus persicae Sulz .Draga and Lesita vacs .were however more suscept­ible . Timate potato plants were more attractive to Empoasca decipiens Paoli. Potato plants of Nicola, Baraka, Draga and Spunta cultivars were not infested by this pest .Timate potato var. was more susceptible to Thrips tabaci Lind. The lowest average numbers of thrips insects oc­curred on Nicola and Baraka var. in 1991 and 1992 , respectively. Serri­na var. showed the highest level of resistance to Bemisia tabaci (Genn.). Lesita Var. was the lowest in this respect. Tetrancychus sp. attacked potato leaves of all tested cultivars in the first year of study , while in the second, Timate was the only cultivar invaded by this pest. in winter plantation, A. gossypii insects prefered winter potato plants of Spunta and Serrina cultivars more than the other tested culti­vars. Draga var. was the most susceptible to infestation with A.. c racci - vora. On the other hand , Timate potato var. was not infested by this species of aphid. M. persicae insects occurred in high numbers on Draga potato plants in both years. Baraka var. in 1991 and Timate var. in 1992