Photosynthesis and productivity of cotton under silverleaf whitefly stress

The silverleaf whitefly (SLW), Bemisia argentifolii (Bellows and Perring), has been a severe pest of numerous field and vegetable crops for many years. Nevertheless, little has been reported on the complex interactions between SLW and its host plants. This study was aimed at investigating the effects of SLW on cotton (Gossypium hirsutum L.) photosynthesis and productivity under various irrigation and N fertilization regimes. Cotton plants (cv. Siv'on) were examined during an entire growing season in two factorial-designed screenhouse experiments consisting of two irrigation regimes (I) x two N application rates x two SLW levels (noninfested vs. infested). Buildup of the SLW population was markedly higher on N-fertilized plants than on N-deficient plants. Seed cotton yield was reduced by SLW infestation under all combinations of I x N treatments by about 40%. Yield reduction (noninfested minus infested) was significantly correlated with the number of SLW adults on the maximally infested leaf at peak flowering (r² = 0.94, P < 0.05 in 1995; r² = 0.91, P < 0.05 in 1996). Photosynthetic rate decreased 50% at about 60 d after SLW introduction. The relative photosynthetic rate (infested/noninfested) was significantly correlated with SLW adult density on the maximally infested leaf (r² = 0.72, P < 0.001 in 1995; r² = 0.53, P < 0.01 in 1996). The reduced photosynthetic rate was associated with reductions in chlorophyll variable fluorescence (Fv/Fm) and fluorescence yield. No substantial changes were found in stomatal conductance, intercellular CO₂ concentration, and leaf chlorophyll content. These findings indicate that SLW infestation impairs, either directly or indirectly, the photochemical reaction of the photosynthetic system in cotton plants.