Resistance to sunn pest of 30 wheat genotypes has been evaluated under field conditions during the years 2000 – 2001. The evaluation method consisted of infestation of host plants by sunn pest nymphs under rearing cages. According to means of resistance indices, genotypes Albor ZX, K 6290914 / cno // K 58 / Tob / 3 / Wa , … , A-12-1-32-438 // Rsh / Bb / Kal / Ald " S ", … ranked as resistant and genotypes Kal//Bb/Kal / 3 / Au / 50 E / 3 * Kal / 4 / Brochis / … , Kayson / Glenson were grouped as susceptible. To study the relationship between resistance of wheat genotypes and abundance of starch granules, the small granules (1 – 10 ?) and large ones (10 –30 ?) have been counted in a definite area of undamaged as well as damaged flour in studied genotypes. Results showed that there are significant differences among studied genotypes regarding abundance of starch granules in undamaged as against damaged grains. Damaged grains showed 36.9 % decrease of small granules indicating sunn pest feeds generally on this size granules. According to results of analysis of correlation, genotypes carrying larger granules in their undamaged grains and which lose less small starch granules are relatively more resistant. Thus evaluation and preliminary selection of varieties and lines resistant to sunn pest seems to be feasible by measuring the number of starch granules in damaged and undamaged grains. The relationship between wheat genotypes and the abundance of starch granules has been determined using ridge regression. The following linear equation shows this relationship, in which R, x1 and x2 are the resistance index, percent reduction of small granules in damaged kernels and the ratio of large to small granules in uninfected kernels respectively.
R=5.5 -./.4(x1)+ 9.79(x2)
The resistance index calculated by means of the above equation would vary between 2-8. Genotypes having the resistance indices of 2 -3.5, 3.5 - 5, 5- 6.5 and 6.5 - 8 are susceptible, semi susceptible, semi resistant and resistant respectively.
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