Resistance Of Transgenic Chi+Glu Cotton On Verticillim Wilt And Effects On Biodiversity In Cotton Field

Stable cotton variety61217-1into which was transferred the chitinase and glucanase bivalent geneby the Institute of Cotton Research in Chinese Academy of Agriculture Sciences, was studied. Theacceptor CCRI24and Lumian28, with a transgenic Bt gene, were used as controls. Between2009and2010, the chitinase-glucanase transgenic cotton line with resistance to Verticillium wilt disease wasanalyzed for its response to non-target disease (seedling disease, premature senescence, boll disease andleaf spot), insect damage in the field (aphid, red spider, capsid and cotton bollworm), and its mainnatural enemies (ladybird, floret bug and lacewing). The microbial flora of the soil was also studied.This provided a basis for the safety evaluation of transgenic cotton.Main conclusions:1. Resistance to Verticillium wilt disease was significantly enhanced in cotton strain61217-1.Compared with receptor CCRI24, the incidence and average disease index of line61217-1decreasedby53.5%and61.6%, respectively. The incidence and average disease index of line61217-1declined by39.1%and47.9%, compared with Lumian28carrying the Bt gene. Thus, it provided good resistance towilt disease in the field. The chitinase-glucanase transgenic cotton line was much more resistant toVerticillium wilt than the receptor material during the whole growth period, implying that thechitinase-glucanase gene was expressed stably during the whole growth period.2. The rate of seedling death of the transgenic disease-resistant cotton was3.7–6.8percentage points lower than the receptor material, and0.6–8.2percentage points lower thanLumian28. In addition, it had a significantly lower rotten bell rate:9.8–16.6percentagepoints lower than the receptor material. Thus, the transgenic cotton not only had improved resistance toVerticillium wilt, but also showed improved resistance to seedling and boll disease.3. At the blossoming and boll forming stage, the leaf spot disease index of cotton61217-1wassignificantly higher than receptor CCRI24and Lumian28. Moreover, the index of Premature Senilitywas slightly higher than receptor CCRI24and Lumian28. Thus, transformation of cotton with thedisease resistant bivalent gene might lead to early aging and increased susceptibility to leaf spot disease.4. During the two years of this study, the number of summer ecotype and the second generationbollworm observed on the bivalent transgenic disease-resisting cotton was significantly lower than onCCRI24. This indicated that the presence of the bivalent transgene could significantly reduce thedamage caused by summer ecotype and second generation bollworm. There was no significantdifference between CCRI24and Lumian28in the occurrence of seedling aphids. The occurrence ofthree generations of larvae was not consistent. The number of H. armigera eggs on61217-1increasedcompared with CRI24and Lumian28. The introduction of the bivalent transgene had different effectson the various morphological stages of the same pest and the mechanism of action requires furtherstudy.5. There were fewer capsids in the chitinase-glucanase transgenic cotton line and Lumian28thanin receptor CCRI24. The number of red spiders was not significantly different among the three strains.The damage caused by red spiders was much more severe in2010and the transgenic cotton had a tendency towards more damage compared with CCRI24. The occurrence of red spider had a significantcorrelation with cotton that was damaged by drought. Red spider might have occurred as a spot film, butthis conclusion requires further verification.6. Compared with receptor CCRI24, the occurrence of adult ladybirds on the chitinase-glucanasetransgenic cotton line was not consistent over the two-year study period. The number of larval ladybirdsand lacewings was reduced, but not significantly. There was no effect on the presence of the Floret bugon the chitinase-glucanase transgenic cotton.7. Compared with receptor CRRI24and Lumian28, the cotton carrying the bivalent gene had aslight, but not unfavorable, effect on soil microorganisms. During the different growth stages of cotton,the rhizosphere soil pH was nearly constant. Furthermore, the soil pH of cotton61217-1was lower thanthat of receptor CCRI24, i.e., the rhizosphere soil pH of the transgenic cotton tended towards acidity.As mentioned above,recipient variety resistant to Verticilliumwillt was promoted significantly withreducing seeding disease and boll rot because of double gene(Chi+Glu) mediation. Besides, the numberof summer ecotype and the second generation of cotton bollworm larvae decreased obviously. While theeffects on other diseases, pest,natural enemies and soil microorganism were not obvious.