Impacts of early-season square abscission on the growth and yield of transgenic Bt cotton under elevated CO2

A field study was carried out to quantify the compensation capacity of Bacillus thuringiensis (Bt)-transgenic cotton to simulated damage by manually removing squares during the early growing season in 2004 and 2005 in combination with CO2 levels (ambient CO2 and elevated CO2). Treatments included: initial squares were wholly (100%) removed manually for 1 week (i.e., SR1 treatment) and for 2 consecutive weeks (i.e., SR2 treatment). Plant leaf area was measured every 2 weeks, and plant root, stem, leaf, shatters, boll dry weight and lint yield and maturity were measured at harvest. Significantly higher leaf area per plant was observed on each sampling date for SR1 and SR2 treatments compared with control (SR0) treatment in 2004 and 2005 under elevated CO2. Significantly higher lint yield and maturity were observed for SR0, SR1 and SR2 treatments under elevated CO2 in 2004 and 2005. CO2 concentration and square removal significantly affected plant lint yield and maturity. Moreover, the interaction between CO2 concentration × square removal had a significant effect on plant leaf dry weight, lint yield and maturity. Our results indicated that transgenic cotton plants can compensate for the manual removal of 100% of the initial squares for 1 and 2 weeks under ambient and elevated CO2.