| Potential weediness is one of ecological impact of genetically modified crops(GMO).There are two channels by which GMO could become a weed,one is weediness in the crop itself,another one is transgenes escape into weedy relatives through pollen-mediated gene flow.There are a lot of reports on weediness of mono-trait transgenic crops.However,rare research has been reported on the weediness of the stacked-traits transgenic crops.Gene stacking refers to the process of combining two or more genes of interest into a single plant.Due to the complex relationship between multiple genes,weediness risk of stacked-gene crops may be enhanced.Therefore,weedniess assessment on gene-stacked crops must undergo a pre-market safety assessment before approval can be given.The first gene stacked rice variety used in the experiment was insect and herbicide-resistant rice B2A68,which cultivated by Institute of subtropical agriculture,the Chinese academy of sciences.B2A68 was obtained by transformed a connected a synthetic insect resistant gene Cry2Aa#and glufosinate resistant gene Bar to receptor rice D68 using agrobacterium-mediated method.B2A68 displayed a high-level resistant to glufosinate and target insect.The other transgenic rice was TIC-19,cultivated by National key laboratory of crop improvement,Huangzhong agricultural university,which obtained by transformed combined insect-resistant gene Cry 1C*and herbicide resistance gene Bar into an elite indica CMS restorer line MH63 using agrobacterium-mediated method.Field experiment indicated that T1c-19 showed high-level resistant to glufosinate and target insect(stemborers and leaffolders).Both of B2A68 and T1c-19 have the possibility of commercialization.The potential weediness of B2A68 and Tlc-19 were studied in Nanjing area in 2012 and 2013,respectively.And in 2014,the fitness of F1 hybrids between Tlc-19 or MH63 as male plants and three weedy rice biotypes(Maoming MM,Taizhou TZ,Yiyang YY)as female plants(named F1+ with T1c-19 as male plants and F1-with MH as male plants)were evaluated in different conditions.The results can provide reliable experimental data for evaluation on weediness of the two stacked traits of transgenic rice.And also provides the experimental basis for formulation of weediness in the evaluation standard of environment safety.The main results are as follows:The possibility of weediness on B2A68.To evaluate potential ecological risk of weediness for gene stacked rice B2A68,the survival and reproductive ability,seed shattering,seed germination rate,seed viability of the transgenic insect-resistant and glufosinate-tolerant rice B2A68 was carried out in the field to compared with glufosinate-tolerance rice Bar-68 and conventional rice ninggen46(CR).The result showed that whatever in favorable season or in unfavorable season,the survival and reproductive ability of B2A68 was no significantly different with Bar-68 in direct seeding or transplanting field,and B2A68 didn't have more competitive ability than CR.The seed shattering of B2A68 was similar to Bar-68,both of them were higher than that of CR significantly,but the shattering of the three rice varieties were at a same level.There was no volunteer plant found in the experiment filed.The germination rate was no significantly different among the three rice varieties and was higher than 90%at 7 days after sowings.Seed viability of three rice varieties decreased with time under shallow or deep bury.Seed viability of B2A68 and Bar-68 decreased faster than that of CR.It is concluded that the potential weediness of B2A68 was low in Nanjing,China..The possibity of weediness on TIC-19.In field conditions,stacked(insect and herbicide-resistant)transgenic rice T1c-19,its receptor rice Minghui63(MH63)and a local indica cultivar Feng-liang-you-xiang-No.1(CR)was compared on survival competition ability(plant height,tiller),reproduction ability(pollen viability,panicle length,filled grain number),seed overwintering ability,shattering,volunteer seedlings for assessing the weediness of stacked transgene rice T1c-19.The results showed that,in direct seeding and transplanting rice,T1c-19 and its receptor were no significantly different in survival competition ability,reproduction ability,and significantly lower than the conventional rice.The seed shattering of T1c-19 and MH63 were less than 3%,significantly lower than CR.Seed dormancy of three rice lines were weak.The seed viability of the three rice lines decreased from 90%to less than 40%under shallow or deep bury after 2 months,and no alive seed detected in 6 months,which indicated that the seed viability was not strong.There was no volunteer plant found in the experiment filed.Exogenous insect resistance and herbicide tolerant genes did not induce competitive advantage to transgenic rice T1c-19,the potential weediness of T1c-19 was low in Nanjing.Fitness of F1 hybirds weedy rice×Tlc-19:A:Sexual compatibility between Tlc-19,MH63 and weedy rice:Six kinds of F1 were obtained with T1c-19 or its receptor rice MH63 as male parent and three weedy rice biotypes as female parent(Maoming MM,Taizhou TZ,Yiyang YY)by hand pollination.The seed setting rates were among 41.7%-88.7%between Tlc-19 and three weedy rice biotypes,which were similar to these between MH63 and three weedy rice biotypes.The results indicated that transgenic rice and three weedy rice biotypes had high sexual compatibility,and transgene did not affected sexual compatibility between MH63 and three weedy rice biotypes.B:Impact of stacked gene on weedy rice:In pure plot under natural insect pressure(insect pressure index 18.4%),F1(+)showed a fitness benefit compared to(F1-)on filled grain number per panicle and yield per plant.On composite fitness,F1TZ+ and F1MM+ were significantly higher than F1TZ-and F1MM-,the composite fitness of F1 YY+ was similar to F1YY-.Without insects pressure(0%),the height,the area of flag leaf,the number of filled grain per panicle and the yield per plant,finally the composite fitness of F1MM+were significantly lower than that of F1MM-,showed significantly fitness cost.However,the composite fitness of F1TZ+ and F1YY+ was no significant different with that of F1TZ-and F1YY-.In mixed plot under natural insect(13.3%),F1TZ+ showed significant fitness benefit compared to F1TZ-,but F1MM+ and F1YY+ had no significant different with F1MM-and F1YY-on composite fitness.In mixed plot without insect pressure,the fitness of F1MM+ was lower than that of F1MM-significantly,but F1TZ+ and F1YY+ was not different with F1TZ-and F1YY-on composite fitness.These above results indicated that environmental pressure and genetic background of weedy rice impact on composite fitness of F1+ with stacked gene.In pure or mixed plot,under natural insect pressure,three F1+ had significant greater composite fitness than their respective weedy rice,and showed fitness benefit.Without insect pressure,composite fitness of F1+ was significantly greater or similar compared to their corresponding weedy rice counterpart.C:Impact of stacked gene on cultivated rice.There was no significant difference between the T1c-19 and its receptor cultivated rice MH63 with or without insect pressure,and the result showed that stacked gene did not affect composite fitness of MH 63 significantly.D:Composite fitness of F+ and Tlc-19 affected by selection pressure:F1+ and Tlc-19 had similar composite fitness with and without glufosinate selection pressuret.The composite fitness of F1TZ+ was significant higher with insect pressure than without it.Insect pressure did not affect on composite fitness of F1MM+,F1YY and T1c-19 significantly.Double selection pressure(glufosinate pressure + insect pressure)did not have a significant impact on composite fitness of Tlc-19 and F1+.To sum up,the surviving competitive ability of insect-and herbicide-resistant stacked transgenic rice B2A68 and Tlc-19 were no significant different to that of corresponding receptor rice,which indicated the potential weediness of gene stacked rice was low.F1+showed a higher or similar composite fitness compared to respective F1-,and higher composite fitness compared to respective weedy rice under the natural insect pressure.F1+showed a higher or similar composite fitness compared to respective F1-under no insect pressure.The environmental selective pressure did not impact on composite fitness of F1+ significantly.The stacked genes did not affect fitness of cultivated rice with or without the natural insect pressure. |
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