Conspecific weeds that permanently infest worldwide agroecosystems are evolved from their crop species.These weeds cause substantial problems for crop production by competing for resources in agricultural fields.Weedy rice represents such a conspecific weed infesting rice ecosystems,and causing tremendous rice yield losses owing to its strong competitiveness and abundant genetic diversity,likely resulted from its complex origins.Here,we report the use of chloroplast DNA(cpDNA)fingerprints to determine whether weedy rice is evolved from its wild(exo-feral)or cultivated(endo-feral)rice progenitor as the maternal donor in recent hybridization events.In addition,we also applied nuclear simple sequence repeat(SSR)markers to confirm the exo-feral or endo-feral origins of weedy rice accessions determined by the cpDNA fingerprints.We found that the studied weedy rice accessions evolved either from their wild or cultivated rice progenitor,as the maternal donor,based on the cpDNA network and structure analyses.Combined analyses of cpDNA and nuclear SSR markers indicated that a much greater proportion of weedy rice accessions had the endo-feral origin.In addition,results from the genetic structure of nuclear SSR markers indicated that weedy rice accessions from the endo-feral pathway are distinctly associated with either indica or japonica rice cultivars,suggesting their complex origins through crop-weed introgression.The complex pathways of origin and evolution could greatly promote genetic diversity of weedy rice.Therefore,innovative methods should be developed for effective weedy rice control.
Nan YaoZhe WangZhuo-Jun SongLei WangYong-Sheng LiuYing BaoBao-Rong Lu
Ecological impact of transgene flow into pop- ulations of wild/weedy relatives is associated with fitness effects in hybrid progeny. Most studies assessing fitness effects focus essentially on early-generation hybrid progeny. However, whether the transgenes remain effective and durable in advanced generations of hybrid progeny remains unclear. We conducted a common garden experi- ment with Fs-F7 hybrid progeny derived from crosses between insect-resistant transgenic （Bt/CpTI） rice and weedy rice, to examine their insect resistance and fitness effects of transgenes on progeny. Hybrid progeny were grown under different insect pressures and cultivation modes where insect damage and fitness-related traits were measured in the same growth season. Plants with transgenes showed significantly lower insect damage （10 % vs. 32 %） and higher fecundity （551 vs. 392 seeds/plant） than those without transgenes in the efficacy of transgenes Fs-F7 populations, suggesting for insect resistance. Fitness benefits of the transgenes were similar among the Fs-F7 populations, indicating the stability of transgenic effects. A positive correlation between insect index and fecundity change was detected, stressing the important role of ambient insect pressures in assessing fitness effects caused by insect-resistance transgenes. Our results have important implications for assessing ecological impacts caused by transgene flow to wild/weedy relatives. For cost-effec- tiveness, the experimental estimation of fitness effects is probably sufficient based on data from hybrids in early generations. Given that fitness effects of insect-resistance transgenes are associated with ambient insect pressure, ecological risk assessment on transgene flow should consider this variable in experimental design, reasonably reflecting actual situations in wild/weedy populations.
Xiao YangLei LiXing Xing CaiFeng WangJun SuBao-Rong Lu
