Abstract
Reduced plant productivity induced by silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring, is often associated with reduced net photosynthetic rate (P n ). This study was aimed at characterizing the effects of SLW on photosynthetic activity in cotton and the underlying mechanisms. Cotton (Gossypium hirsutum L. cv. Siv'on) plants were examined under SLW-infested and non-infested conditions and subjected to measurements of gas exchange, chlorophyll content and chlorophyll fluorescence. SLW infestation significantly reduced the P n of cotton by 22-54% throughout the day as well as throughout most of the examined ranges of photosynthetic photon flux density (PPFD) and CO 2 concentrations. Stomatal conductance was also reduced by SLW injury, while intercellular CO 2 concentration (C i ) was not affected, suggesting that stomatal limitation is not the major factor limiting P n . This conclusion was further supported by estimates of stomatal limitation, based on P n /C i curves, which were not affected by SLW infestation. On the other hand, non-stomatal limitation induced by SLW was over 2-fold higher than stomatal limitation. Chlorophyll a and b contents were not modified by SLW infestation. Fluorescence ratio (F v /F m ) and the effective quantum yield of PSII were reduced by less than 10%; thus, impaired photochemical reaction is probably not the only factor limiting P n under SLW infestation. In conclusion, SLW-induced P n reduction in cotton was due to non-stomatal factors, possibly induced by impaired carbon fixation and/or carbohydrate export.
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