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 caused by transgene flow from genetically engineered （GE） crops to their wild rela- tives is largely determined by the fitness effect brought by a transgene. To estimate such impact is critical for the eco- logical risk assessment prior to the commercialization of GE crops. We produced F1 and F2 hybrid descendants from crosses of two insect-resistant GE rice lines （Bt, Bt/CpT1） and their non-GE rice parent with a wild rice （Oryza ruff- pogon） population to estimate the transgenic fitness. Insect damages and life-cycle fitness of GE and non-GE crop- wild hybrid descendants as well as their wild parent were examined in a common-garden experiment. No significant differences in insect damages were observed between the wild rice parent and GE hybrid descendants under high- insect pressure. The wild parent showed significantly greater relative survival-regeneration ratios than its GE and non-GE hybrid descendants under both high- and low-in- sect pressure. However, more seeds were produced in GE hybrid descendants than their non-GE counterparts under high-insect pressure. Given that the introduction of Bt and Bt/CpT1 transgenes did not provide greater insect resistance to crop-wild hybrid descendants than their wild parent, we predict that transgene flow from GE insect-resistant rice to wild rice populations may not cause considerable ecolog- ical risks.
Lei LiXiao YangLei WangHuanxin YanJun SuFeng WangBao-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
Weedy rice (WR,Oryza sativa L.f.spontanea)is a noxious agricultural weed,infesting rice fields worldwide and causing tremendous yield losses of cultivated rice.However,little is known about the relationship between genetic diversity and distribution of WR populations across a wide latitudinal gradient,in addition to its reasons for genetic differentiation.To determine the distribution of genetic diversity and differentiation,we analyzed 20 WR populations collected from wide geographic ranges of rice-planting regions across Northeast,Jiangsu,and Guangdong provinces of China,and Sri Lanka,based on 20 simple sequence repeat loci.Our results indicated a significant negative correlation (R =0.84,P <0.01)between genetic diversity and latitudinal locations of WR populations.The Mantel test (R2 =0.49,P <0.01)showed distinct groupings of WR populations from different rice-planting regions,fitting an isolation-by-distance pattern.In addition,the STRUCTURE analysis and principal coordinates (PCoA)analysis indicated considerable genetic differentiation of WR from different rice-planting regions,which was associated with the types of co-occurring rice cultivars.We conclude,based on the above results,that WR genetic diversity is affected by the latitudes where WR populations are located.The genetic differentiation of WR populations is determined by their spatial distances and co-occurring rice cultivars.Such a pattern of genetic diversity and differentiation across different regions might facilitate the design of effective WR control,in addition to understanding the adaptive evolution of this weed.
Zhe WangMin-Jie FuHai-Ge ZhuYue ZhuXiang-Xiang ZhaoBao-Rong Lu
