Transgenic Cottons Show Differential Responses to Drought-Stress and Herbivory by Western Flower Thrips

Recent drought conditions in Texas and continuous depletion of the Ogallala aquifer have highlighted the need for novel cotton cultivars that are well-adapted to reduced irrigation.  Abscisic acid is a plant hormone that plays a key role in regulating plant responses to drought, and transgenic cotton cultivars that over-express this hormone have recently been developed.   In the laboratory, we investigated three of these transgenic cultivars and the wild-type (WT) for responses to conditions of drought and herbivory by a key early-season pest in cotton, Western Flower Thrips (WFT).  We hypothesized that under drought conditions stomates will close to minimize transpiration and this will cause leaf surface temperatures to increase.  Therefore, plants were assayed for responses to drought and recovery (24h post water) by measuring stomatal apertures and leaf surface temperature (LST).  To test for an effect of periodic drought-stress on susceptibility to herbivory, we conducted Petri-dish bioassays by exposing WFT to excised cotton leaves from the different cultivars.  Drought-treatment plants had significantly higher LST compared to well-watered in all cultivars except for one, which was a transgenic.  Recovery from drought (24h post watering) showed a marked reduction in LST for all cultivars and drought-treatments.  However, for some cultivars, LST in drought-treatments did not recover completely and remained elevated relative to those in well-watered treatments. Results of the herbivory bioassay showed that some transgenic cultivars were more susceptible to WFT than others based on comparisons of feeding, thrips weight, hatched eggs and total number of eggs laid.  Drought-treatment rarely caused any detectable effects on the feeding and fitness of WFT across all cultivars.  Summarizing, our results highlighted how different transgenic events in the same genomic background can result in substantial variation in the plants’ response to drought as well as susceptibility to a key pest.