Changes in Chlorophyll a Fluorescence Induction Kinetics in Cereals Infested with Russian Wheat Aphid (Homopetra: Aphididea)

Abstract

Plant entries that previously had tested resistant or susceptible to Russian wheat aphid, Diuraphis noxia (Mordvilko), were used to evaluate the effect of aphid feeding on leaf chlorophyll content and in vivo chlorophyll fluorescence induction kinetics. D. noxia feeding for 96 h caused significant reductions in chlorophyll a, chlorophyll b, and total chlorophyll content in susceptible wheat (‘Avon’, ‘TAM W-101’) and barley (‘Wintermalt’). Total chlorophyll content and constituent chlorophyll a and b levels were not significantly affected by D. noxia in resistant wheat (PI 366616, PI 372129) or barley (PI 366450) and in neither resistant (PI 386156) nor susceptible (‘Beagle 82’) critical. D. noxia infestation resulted in significant alterations of the primary fluorescence induction transients. When compared with non infested control plants, infested susceptible wheat and barley showed significantly increased non variable fluorescence (F0) and decreased maximal fluorescence (Fm) and variable fluorescence (Fv). In contrast, values for these parameters did not differ significantly among the infested and non infested controls of resistant plants. When compared with control plants, the photochemical efficiency of photo system II (F/Fm) and the half-rise time from Fo to Fm (t1/2) were reduced significantly in the infested susceptible entries but remained relatively unchanged for the infested resistant cultivates. No significant differences between infested and non infested plants were observed in the measured chlorophyll fluorescence parameters for either the resistant or the susceptible critical, 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 photosyntheses from the plant. The substantial decrease in F/Fm following aphid infestation for the susceptible wheat and barley indicated a significant decrease in the capacity and efficiency of the primary photochemistry of photo system II.