CHANGES IN CHLOROPHYLL-A FLUORESCENCE INDUCTION KINETICS IN CEREALS INFESTED WITH RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE)

Plant entries that previously had tested resistant or susceptible to R ussian wheat aphid, Diuraphis noxia (Mordvilko), were used to evaluate the effect of aphid feeding on leaf chlorophyll content and in vivo c hlorophyll fluorescence induction kinetics. D., noxia feeding for 96 h caused significant reductions in chlorophyll a, chlorophyll b, and to tal chlorophyll content in susceptible wheat ('Pavon', 'TAM W-101') an d barley ('Wintermalt'), Total chlorophyll content and constituent chl orophyll a and b levels were not significantly; affected by D. noxia i n resistant wheat (PI 366616, PI 372129) or barley (PI 366450) and in neither resistant (PI 386156) nor susceptible ('Beagle 82') triticale. D, noxia infestation resulted in significant alterations of the prima ry fluorescence induction transients. When compared with noninfested c ontrol plants, infested susceptible wheat and barley showed significan tly increased nonvariable fluorescence (F-0) and decreased maximal flu orescence (F-m) and variable fluorescence (F-v). In contrast, values f or these parameters did not differ significantly among the infested an d noninfested controls of resistant plants. When compared with control plants, the photochemical efficiency of photosystem II (F-v/F-m) and the half-rise time from F-0 to F-m (t(1/2)) were reduced significantly in the infested susceptible entries but remained relatively unchanged for the infested resistant cultivars. No significant differences betw een infested and noninfested plants were observed in the measured chlo rophyll fluorescence parameters for either the resistant or the suscep tible triticale, which implied a much different resistance mechanism(s ) to D. noxia. The results of this investigation suggest that D. noxia damage goes beyond the simple removal of photosynthates from the plan t. The substantial decrease in F-v/F-m following aphid infestation for the susceptible wheat and barley indicated a significant decrease in the capacity and efficiency of the primary photochemistry of photosyst em II.