Abstract
The quality of decomposing plant materials may affect the soil community structure. The aim of the study was to determine the impact of decomposing Bt cotton and its isoline on soil nematode diversity. Bt cotton (06Z604D), isoline (99M03) and HART 89M (local non-Bt cotton cultivar) were planted for two seasons in a completely randomized block design in a confined field trial at Mwea, Kenya. After harvest the plant material was incorporated into soil and the nematode diversity was determined. The presence of Bt protein was evaluated using ELISA and insect bioassays. Abundance of bacteria feeding nematodes was significantly (p<0.05) high but to a smaller extent in the Bt cotton plots (53.7% and 52% in the first and second season respectively) than in isoline (42.8% and 45% in the first and second season respectively). Insect bioassays detected Bt protein in the Bt cotton plots during the entire decomposition period in both seasons. There were no significant differences in nematode trophic groups composition between isoline and HART 89M. The effect of Cry2Ab2 and Cry1Ac protein in decomposing Bt cotton litter on soil nematodes was minimal. The study provides a basis for future studies on the impact of genetically engineered plants on soil nematodes in Kenyan agroecosystems.
Highlights
Transgenic crops are commercially cultivated in different countries and one of the main traits expressed in the plants is insect resistance
The insect bioassay through inhibition of larval growth was able to detect Bt protein in soil throughout the decomposition period compared with ELISA which detected Cry1Ac and Cry2Ab2 in the earlier months only
The lack of protein detection by ELISA in later months of decomposition may have been caused by protein extraction inefficiencies due to the presence of soil particles
Summary
Transgenic crops are commercially cultivated in different countries and one of the main traits expressed in the plants is insect resistance. The ecological concerns include gene flow to local cultivars, resistance development, invasiveness and effects on non target organisms such as nematodes (Mina et al, 2008). Decomposing transgenic plants may have a direct effect on soil microorganisms through exposure to the Bt protein and indirectly through unintended changes in the plant make up during transformation (Mina et al, 2008). According to Saxena & Stotzky (2001), Bt cotton decomposes less than its near isogenic line. They further argue that a decrease in decomposition would result in improvement of soil structure and reduction in soil erosion due to accumulation of organic matter.
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