Risk Assessment Of Gene Flow From Herbicide-resistant Genetically Modified Rice And Oilseed Rape Respectively To Weedy Rice And Wild Brown Mustard Under Artificial Cultural Conditions Through Ecological Fitness

One of the ecological concerns over herbicide-resistant genetically modified crops is gene flow to their wild/weedy relatives,resulting in a menace to local biodiversity.For this reason,it is essential to assess potential risk before their release in field.Crop-to-wild/weed gene flow mediated by pollen involves hybridization,backcross and fitness of their hybrids. Whether or not wild/weedy relatives,after introduction of the transgene by hybridization, are capable of living their own lives in their habitat hinges on their ecological fitness.We studied their performance under artificial cultural conditions,from the angle of fitness,in vegetative and reproductive stages of filial generations with herbicide-resistant gene between GM rice(Oryza sativa) and weedy rice(O.sativa f.spontanea),and backcross ones between GM oilseed rape and wild brown mustard(B.juncea var.gracilis Tsen et Lee),for the purpose of analyzing the fitness differences between GM crops and their wild/weedy relatives to estimate likelihood of successful gene flow.Research on fitness of progeny of two different kinds of GM crops is conducive to reveal its universal significance in safety assessment of GM crops.The main results are given as follows:1.Fitness of F₁,F₂ hybrids between weedy rice and GM riceIn this experiment our work compared fitness components of parents and F₁,F₂ hybrids between three types of weedy rice M4,AH,share177 and two herbicide-resistant GM cultivars Y0003,99-t.We measured plant height,tiller number/plant,stem diameter,flag leaf length,flag leaf width,flag leaf area,net photosynthetic rate in vegetative growth,and pollen viability,panicle number/plant,spikelet number/panicle,seed set of self-pollination, seed shattering,panicle length,grain length,grain width,grain thickness,100-grain weight in reproduction.Our results showed that 4×Y F₁ had the composite fitness value of 1.12, reciprocal cross Y×4 F₁ of 1.1.No apparent differences were found between them and their GM parent Y0003's 1.2,whereas significant ones were detected when compared to their weedy parent M4's 1.However,composite fitness of F₂ generations fell down.4×Y F₂ dropped off to 1.02,Y×4 F₂ to 1.04,and there were no considerable differences between them and their weedy parent M4.It suggested that F₂ progeny lowered their fitness to approach their weedy parent's.In other words,F₂ offspring performed in the similar way as weedy type.Therefore,risk of gene contamination caused by gene flow from GM rice to weedy one should not be slighted.Fitness differences between hybrids from original and reciprocal crosses were not statistically evident.Weedy parent could exert greater influence than GM one's on performance of their progeny.Moreover,hybrids were likely to be latent candidates for volunteers.2.Fitness of F₁,F₂ hybrids between weedy rice and GM riceIn this experiment our work compared fitness components of parents and F₂,F₃ hybrids between two types of weedy rice M4,AH and two herbicide-resistant GM cultivars Y0003, 99-t.We measured plant height,tiller number/plant,stem diameter,flag leaf length,flag leaf width,flag leaf area,above-ground biomass,chlorophyll fluorescence(Fv/Fm) in vegetative growth and pollen viability,panicle number/plant,spikelet number/panicle,seed set of self-pollination,seed shattering,panicle length,grain length,grain width,grain thickness,100-grain weight in reproduction.Our results showed that if composite fitness of weedy parent was defined as "1",F₂ and F₃ offspring from 4×Y cross reached the level respectively of 0.93 and 0.95,AH×Y of 0.94 and 1.02,4×99-t of 0.98 and 1.04,AH×99-t of 0.92 and 0.99.Fitness of all the hybrids was not statistically different from their weedy parent's.It indicated that F₃'s fitness,instead of falling further,remained close to weedy type's level,giving a representation of its high plant vigor.Therefore,risk of gene contamination caused by gene flow from GM rice to weedy rice cannot be despised. Performance of hybrids were affected strongly by the characteristics of weedy parent,while little by GM parent's and reciprocal cross.Again,it proved that hybrids were likely to be latent candidates for volunteers.3.Fitness of second-,third-generation backcross hybrids between GM oilseed rape and wild brown mustardIn this experiment our work compared fitness components of recurrent parent and second-,third-generation backcross hybrids between wild brown mustard and GM oilseed rape.We measured separately the traits in single,double and mixed planting modes, including bolting period,plant height,branch number/plant,stem diameter,rosette diameter, chlorophyll fluorescence(Fv/Fm) in vegetative growth,and flower number/plant,pollen viability,silique number/plant,silique length,seed number/silique,seed fertility,100-seed weight in reproduction.Our results show that gene introgression from wild brown mustard by successive backcross helped composite fitness of each backcross progeny revert to the level of wild brown mustard,which meant that they got great potentialities to be capable of making their own living in nature.Consequently,they became great menaces to biodiversity of their wild relatives around.The effects of reciprocal backcross and planting mode on composite fitness,unfortunately,could not be observed in such an experimental design.Furthermore,backcross offspring were likely to be latent candidates for volunteers.4.Fitness of fourth-generation backcross hybrids between GM oilseed rape and wild brown mustardIn this experiment our work compared fitness components of recurrent parent and different types of fourth-generation backcross hybrids between wild brown mustard and GM oilseed rape.We measured separately the traits in single,double and mixed planting modes,including bolting period,plant height,branch number/plant,stem diameter,rosette diameter,above-ground biomass in vegetative growth,and florescence,silique number/plant,silique length,seed number/silique,seed fertility in reproduction.Our results showed that gene introgression from wild brown mustard by successive backcross helped composite fitness of each backcross progeny revert to the level of wild brown mustard, which meant that they got great potentialities to be capable of making their own living in nature.Obviously,their existence would severely threaten biodiversity of their wild relatives around.Reciprocal backcross and planting mode,to a certain extent,could work on composite fitness.In conclusion,the filial or backcross generations were nearly the equal of their wild/weedy parent in plant vigor,implying that fitness did not proved a barrier to gene flow from herbicide-resistant GM rice and oilseed rape respectively to weedy rice and wild brown mustard.To make matters worse,there is a hidden danger of their seeds' escaping into volunteers.In view of the risks mentioned above,their large-scale spread in field should be given careful consideration.Besides,taking all possible measures that are practical and effective prevents gene contamination.