Date Published: January 18, 2017
Publisher: Public Library of Science
Author(s): Jun-Yu Luo, Shuai Zhang, Jun Peng, Xiang-Zhen Zhu, Li-Min Lv, Chun-Yi Wang, Chun-Hua Li, Zhi-Guo Zhou, Jin-Jie Cui, Nicolas Desneux.
An increasing area of transgenic Bacillus thuringiensis (Bt) cotton is being planted in saline-alkaline soil in China. The Bt protein level in transgenic cotton plants and its control efficiency can be affected by abiotic stress, including high temperature, water deficiency and other factors. However, how soil salinity affects the expression of Bt protein, thus influencing the control efficiency of Bt cotton against the cotton bollworm (CBW) Helicoverpa armigera (Hübner) in the field, is poorly understood. Our objective in the present study was to investigate the effects of soil salinity on the expression of Bt toxin (Cry1Ac) and the control efficiency of Helicoverpa armigera in field-grown transgenic Bt cotton using three natural saline levels (1.15 dS m-1 [low soil-salinity], 6.00 dS m-1 [medium soil-salinity] and 11.46 dS m-1 [high soil-salinity]). We found that the Bt protein content in the transgenic Bt cotton leaves and the insecticidal activity of Bt cotton against CBW decreased with the increasing soil salinity in laboratory experiments during the growing season. The Bt protein content of Bt cotton leaves in the laboratory were negatively correlated with the salinity level. The CBW populations were highest on the Bt cotton grown in medium-salinity soil instead of the high-salinity soil in field conditions. A possible mechanism may be that the relatively high-salinity soil changed the plant nutritional quality or other plant defensive traits. The results from this study may help to identify more appropriate practices to control CBW in Bt cotton fields with different soil salinity levels.
Soil salinization is an important impediment to sustainable agricultural development [1,2]. The total area of saline land in nearly 100 countries is approximately 1010 million ha, accounting for approximately 25% of the total land area. Because of improper irrigation or poor drainage, approximately 300,000 ha of cultivated land worldwide are affected by secondary salinization . In China, saline-alkaline soil occupies an area of 37 million ha, accounting for 4.9% of the arable land. The recent increase in the area of salinized land, which has reached 9 million ha and represents 6.6% of the total cultivated land area, endangers crop production . Cotton is one of the most important cash crops worldwide and a pioneer crop on salinized land; thus, the cultivation of cotton on saline or alkaline land is a preferred alternative strategy for future agricultural production on a limited land area to guarantee grain crop output . Developing techniques for cotton cultivation on saline or alkaline land has become therefore an important focus of agricultural research in China.
The soil physical and chemical properties and abiotic factors (mechanical wounds, ultraviolet radiation, environmental stress, etc.) [44–46] can affect plant growth and nutrition [18–20]. Host plant nutrition can also modify the plant’s reaction to insects, which can have varied effects on herbivore densities [18,20]. Some studies have indicated that high temperatures [30–32], drought and waterlogging [37,22,34], nitrogen nutrition [47,48] and salinity stress [38–41] can affect the control efficiency and Bt protein content of transgenic Bt cotton. In this study, we focused on the influence of soil salinity on the Bt protein content and control efficiency of Bt cotton and the change in the pest population in the field during the growing season.