Photosynthetic Responses of Wheat, <I>Triticum aestivum</I> L., Plants to Simulated Insect Defoliation During Vegetative Growth and at Grain Fill

Abstract

The impact of different levels of whole plant partial defoliation (WPPD) on the photosynthesis and primary metabolism of wheat,Triticumaestivum L., was evaluated at the vegetative and reproductive (grain-Þlling) developmental stages. Photosynthetic parameters such as photosyn- thesis, stomatal conductance, and transpiration, chlorophyll a suorescence, and plant morphological parameters, such as main stem height, sag-leaf and undefoliated leaf areas, and number of tillers, were recorded 1 h and 1, 9, and 12 d after defoliation in 2004 and 1 h, 3 d, and 6 d after defoliation in 2005. Plants with high defoliation levels (i.e., defoliation 75%) had 21 and 20% greater photosynthesis rates compared with control and low defoliation level treatments, respectively. Our data show that stomatal conductance for sag leaves was not signiÞcantly affected by WPPD. In addition, we did not observe a signiÞcant effect of defoliation on intercellular CO2 concentrations or on transpiration rates remaining sag 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 signiÞcant long-term modiÞcations to growth, morphological, or primary physiological characteristics of wheat plants.