Photosynthetic responses of wheat, Triticum aestivum L., plants to simulated insect defoliation during vegetative growth and at grain fill

The impact of different levels of whole plant partial defoliation (WPPD) on the photosynthesis and primary metabolism of wheat, Triticum aestivum L., was evaluated at the vegetative and reproductive (grain-filling) developmental stages. Photosynthetic parameters such as photosynthesis, stomatal conductance, and transpiration, chlorophyll a fluorescence, and plant morphological parameters, such as main stem height, flag-leaf and undefoliated leaf areas, and number of tillers, were recorded I h and 1, 9, and 12 d after defoliation in 2004 and I h, 3 d, and 6 d after defoliation in 2005. Plants with high defoliation levels (i.e., defoliation > 75%) had approximate to 21 and 20% greater photosynthesis rates compared with control and low defoliation level treatments, respectively. Our data show that stomatal conductance for flag leaves was not significantly affected by WPPD. in addition, we did not observe a significant effect of defoliation on intercellular CO, concentrations or on transpiration rates remaining flag leaf tissue. Similar responses were observed for the overall photosynthesis of defoliated plants during vegetative stages. Whole plant source-sink manipulation of wheat by WPPD during the major plant developmental stages (i.e., vegetative and reproductive) did not elicit any significant long-term modifications to growth, morphological, or primary physiological characteristics of wheat plants.