Host Plant's quality in the food chain of a herbivorous insect influences the insect's life performance, and thus abundance in its populationa photoperiodism cycle of 16 L: 8D hours

Wheat leaf rust (Puccinia triticina Eriksoon) is of the most injurious wheat diseases that prevails throughout areas where wheat is grown. An identification of virulence factors along with differences in the population of pathogen in different wheat growing regions is necessary for an enhancement of resistant cultivars with effective resistant genes to leaf rust. To accomplish the purpose, a leaf rust Trap Nursery containing 37 near isogenic lines in addition to Bolani susceptible cultivar as check were planted under natural infection conditions in Gorgan (with an application of mist irrigation) and Gonabad (with no mist irrigation) locations during 2002-2007. Reaction to the disease of each line was recorded at the flag leaf stage and when infection on the Bolani susceptible cultivar was at its maximum level for infection rate and type. "S" reaction indicated virulence while "O, R, MR and MS" reactions were indicative of as avirulence. Results showed that virulence was detected for genes Lr1, Lr2c, Lr3, Lr3ka, Lr3bg, Lr10, Lr11, Lr12, Lr13, Lr14a, Lr14b, Lr15, Lr16, Lr17, Lr18, Lr20, Lr21, Lr22a, Lr22b, Lr23, Lr24, Lr26, Lr30, Lr32, Lr33, Lr34 and either Lrb at one or both Gorgan and Gonbad locations. Virulence was observed for genes Lr3, Lr10, Lr14b, Lr17, Lr18, Lr26 and Lr34 only at Gorgan site. No virulence was observed for genes Lr2a, Lr2b, Lr19, Lr25, Lr28, Lr29, Lr35, Lr36 and Lr37 at these locations. Avirulence due to the resistance of the above resistant genes provides the possibility of the use of these genes in breeding programs to develop varieties resistant to wheat leaf rust.