Effect of interspecific mixed cropping between transgenic oilseed rape and wild mustard on soil nematode communities

Abstract

As genetically modified (GM) crops are cultivated worldwide, the effects of GM crops on non鄄target organisms are of concern. Interspecific mixed cropping between transgenic and non鄄transgenic crops is generally regarded as a strategy against insects to minimize the development of resistance to otherwise insect鄄resistant transgenic crops. The toxin from Bacillus thuringiensis (Bt) is introduced into the soil primarily through root exudates and by the incorporation of plant residues after harvest, with probable help from pollen. Such incorporation of the toxin poses potential risks to soil organisms, including microbes, nematodes, collembolans, and other invertebrates. However, its effects on non鄄target soil organisms have rarely been assessed. We evaluated the effect on soil nematodes of mixed cropping with transgenic canola Brassica napus L. expressing Bt and wild brown mustard B. juncea. The abundance and genera composition of soil nematodes in the flowering and fruiting period of canola were investigated in five mixed proportions of transgenic canola and wild brown mustard: 0颐100 (A) , 25颐75 (B) , 50颐50 (C) , 75颐25 (D) , and 100颐0 (E). The results showed the following order of genera composition with each treatment: B (30 genera) > C (28 genera) > A (26 genera) > D and E (25 genera). The dominant nematode genera were Acrobeloides and Aphelenchus, accounting for 37. 4% and 12. 3% of total abundance, http: / / www.ecologica.cn respectively. The common and rare groups belonging to 13 and 19 genera accounted for 47. 9% and 2. 39% of the total, respectively. Hirschmanniella appeared only in treatment C. Tylenchus and Heterodera appeared only in treatments A and B. Depending on the trophic structure based on the functional group, fungivorous nematodes formed the largest proportion at 47.5%, followed by bacterivorous, herbivorous, and omnivorous鄄predatory nematodes at 33.7%, 14%, and 4.8% of the total, respectively. The colonizer鄄persister (c鄄p) values of nematodes had the same composition among the five treatments. Further, similar life histories were noted following the treatments. The total number of nematodes was in the range of 141.5-756.0 / 100 cm 3. The total abundance and number of four feeding types of nematodes were not significantly different among treatments. The generic composition and community parameters of nematodes did not differ significantly among the five treatments. The Shannon鄄Wiener diversity index (H忆) , Simpson index (姿) , and evenness index (J忆) of soil nematode communities showed no significant differences among treatments on May 20. However, treatment D showed a high diversity index, dominance, and evenness index on July 4, and the highest Simpson index and evenness index on August 22. Nematode maturity index (MI) was in the range of 2.15-3.63; nematode channel ratio (NCR) was 0.28-0.57 for the three sampling times in each treatment. Thus, the H忆, 姿, J忆, MI, and NCR of the nematodes varied with time. These results suggest that sole cropping or mixed cropping of transgenic canola with wild b...