Genes On The Receptor In Rice (oryza Sativa), Fitness Effects

Transgenes conferring resistance to rice insects have been introduced into pre-commercial lines of rice. The potential of these genes spreading to weedy or wild rice species that occurs near the GM rice becomes a great concern. The persistence of crop genes in wild or weedy rice populations is influenced by the associated fitness costs and benefits. Understanding the balance between yield benefits and possible underlying yield costs that are associated with transgenic cultivars is useful for evaluating crop performance and the fitness of crop-wild hybrid progeny, but few studies have tested for such costs under rigorous experimental conditions. As with other types of transgenic crops, biosafety assessment of GM rice requires information on the extent and consequences of gene flow to wild and weedy relatives of the crop, and whether the transgenes could increase the fitness advantage and thus cause any adverse ecological consequences. As a first step toward understanding the fitness effects of such transgenes on weedy or wild relatives, we carried out potted and field experiments in 2003 and 2004, comparing the growth and fecundity of three types of GM insect-resistant cultivated rice with non-GM control plants under conditions of low versus moderate insect pressure, with or without direct competition between the GM and control lines. We were especially interested in whether advanced-generation transgenic cultivars exhibit any detectable fitness costs that might be transferred to weedy or wild relatives of the crop.In the potted experiments in 2003, insect damage on GM rice lines was lower than that of the non-GM controls, indicating the transgenes may increase the insect tolerance ability for the GM lines. For Bt line, fitness costs for fecundity were undetectable under low insect pressure at the rooftop site. A net fitness benefit of Bt was detected under higher insect pressure at the field site. The Bt plants produced more tillers than the non-GM control, therefore, increased the number of panicles per plant resulting in the significant increase of seed production. For CpTI, fitness effect on seed production was not as significant as Bt gene. Under low insect pressure, fitness cost on seed production was not detected, while under higher insect pressure, CpTI line produced more tillers and thus increased the panicle numbers, but did not exhibit fitness benefit for seed production. This suggests that fitness costs and benefits associated with CpTI were negligible. For Bt/CpTI, fitness effect on seed productionwas greatest. Under low insect pressure, Bt/CpTI plants produced fewer full seeds per plant, and seeds with lower mass than the non-GM controls. Under higher insect pressure, Bt/CpTI plants exhibited net fitness benefits on fecundity in pure competition, but the net benefit for Bt/CpTI plants disappeared in mixed-line competition pots. This findings shows that fitness costs were greater under the mixed competition than pure competition. In the mixed experiment, the fitness costs associated with Bt/CpTI were large enough to offset the fitness advantage that observed in the pure competition.In the field experiments in 2004, GM lines showed notable insect resistance ability. The insect damage by leaf-folder and stem bores was significantly lower than the non-GM controls. Under low insect pressure, the three types of GM lines exhibited various fitness costs on fecundity, whereas under higher insect pressure, fecundity benefits were not detectable.For Bt, fecundity costs were not great in general. Under low insect pressure, fecundity cost was only detected for seed set rate in the pure competition experiment. No other fitness costs were found on other indices associated with fecundity. But it is notable that full seeds per plant and number of panicles per plant of Bt line were lower than the non-GM control in the mixed competition, and the differences were almost significant (P>0.05 and <0.1). Under higher insect pressure, fecundity effects associated with Bt were not detected both in the pure competition and mixed competition. For CpTI, fecundity costs were also not great in general. Under low insect pressure, 1000-grain weight of full seeds for CpTI plants was significantly lower than the non-GM control. Under higher insect pressure, fitness effects on fecundity for CpTI were not detectable. For Bt/CpTI, the fecundity effects were greater than those of Bt and CpTI. Under low insect pressure, the 1000-grain weight of full seeds for the Bt/CpTI plants was significantly lower than the non-GM control in the pure competition, and the seed set rate, full seed weight per plant, 1000-grain weight of full seeds, panicle numbers per plant, and average panicle length for the Bt/CpTI plants were significantly lower than the non-GM control in Mixed competition. Under higher insect pressure, 1000-grain weight of the Bt/CpTI lines was significantly lower than that of non-GM control both in the pure and mixed competitonsIn the field experiments where insecticides applied, plant height and tiller numbers of the Bt plants in various growth stages were significantly lower than the non-GM control, and the fresh biomass at maturity was also lower than the non-GM control. The distinct decrease in tiller numbers at maturity resulted in the reduction of panicle numbers per plant, therefore, significantly reduced the seed production for the Bt plants. The fecundity costs in the mixed competition were greater than that of the pure competition. For CpTI and Bt/CpTI, transgenes exhibited significant negative fitness effects on plant height, but not significant on tiller production, thus caused less fitness costs on fecundity.Fitness effects of insect-resistance transgenes were easier to be detected under mixed competition conditions. In mixed competition experiments, the net costs and benefits on the growth, development and fecundity associated with the transgenes could be more significant than that of the pure. The results suggest that these costs may be little or even negligible in monotypic rice fields, especially when target insects are abundant.Regarding the biosafety assessment on transgenic rice, further experiments should be carried out to detect the fitness effects of transgenes on weedy and wild populations, transgene expression in weedy and wild relatives, and the persistence of transgenes in the weedy and wild populations. This study detected and analyzed the fitness effects of three types of insect-resistance GM rice lines that are ready for commercialization. The findings from this study could provide references for the evaluation on the three types of GM rice lines in some extent. The methods established in this study could also be applied into the further research of the fitness effects of transgenes on weedy and wild relatives. The information of the fitness effects on transgenic rice lines would be helpful for the fitness effect evaluation on weedy and wild relatives of the crop.