Genetic Diversity Of Weedy Rice (O. Sativa F. Spontanea) And Its Effect On Rice Ecosystem

Weedy rice refers to rice plants or populations of O.sativa f.spontanea growing in paddyor other fields as a weedy type,which have an serious effect on rice ecosystem throughreproducing themselves by seed shattering,dormancy,and strong competition ablity againstnatural conditions.Weedy rice is a serious weed in rice-transplanting areas in LiaoningProvince of north China now.Field surveys conducted to define the distribution region ofweedy rice and weedy rice resources were collected from the main rice-growing regions ofLiaoning Province in the autumns 2003-2005.A research has been done at the Rice ResearchInstitute of Shenyang Agricultural University in 2006-2008 to determine the phenotypicdiversity,genetic dversity and population differentiation,origin,the effect on rice paddy ecosystem,germination dynamics of weedy rice.The main results are summarized as follows:1,Weedy rice is easily found in many rice growing areas in Liaoning province inNorth-east China.The distribution of weedy rice among farms is likely to be accomplished byseveral means,including culture,farming,machinery.Weedy rice spread quickly from paddy toother fields as a weedy type in North-east China now.The present paper indicated that weedyrice diffused widely by seed transportation and spread nearly by farming.The results alsoshowed that weedy rice distribute widely in conventional cultivars and was not found inhybrid rice in main rice growing regions of Liaoning.2,A research has been done at the Rice Research Institute of Shenyang AgriculturalUniversity in 2006 to determine the phenotypic diversity of weedy rice.Data were collectedon various morphological variables of weedy rice.The paper indicated considerablemorphological variation among weedy rice collections from Liaoning.This study revealed thatthere is great phenotypic diversity in weedy rice accessions from different regions based onplant height,tillering capacity,panicles,presence of own and other biological traits.Most ofweedy rice have white or red long awn,red pericarp.The weedy rice appears to bedifferentiated into japonica and indica unconspicuously based on six characteristics ofCheng's index.Most of weedy rice was classified into japonica andjaponica-cline types,whileminority was classified into indica-cline.3,Samples of weedy rice have been analysed with 30 SSR makers in comparison to arepresentative to collection of cultivated rice varieties and wild O.rufipongon.The percent ofpolymorphic loci was 86.67% and Shannon' s information index was 0.762,these resultsshowed that the genetic diversity of Liaoning weedy rice was very high.The results alsoshowed that the genetic differentiation of Liaoning weedy rice was very complex based onanalysis with 30 SSR makers.The G发_STvalues was 0.843 suggesting that the main genetic variation of weedy rice resided among populations.Weedy rice populations of Liaoning wereclosely related to japonica cultivated rice varieties but distantly related to wild O.rufipongonand indica cultivated rice varieties.Weedy rice from Liaoning most probably originated fromjaponica cultivated rice varieties planted in Liaoning by natural hybridization and naturalmutation.The weakness of breeding and cultivation methods promoted origin of Liaoningweedy rice.4,Field experiments were conduct to determine effects of season-long interference ofweedy rice densities of 1,3,5,7,and 9 plants/m² on a rice variety Shennong265.Cultivated ricegrain yield were reduced by 44.65%,36.89%,24.67%,17.58%,and 1.37% when weedy ricedensities were 9,7,5,3and 1 plants/m²,respectively.The competition of weedy rice to cultivatedconsiderably reduced rice grain yield when weedy rice densities were 9,7,5 and 3 plants/m²,respectively.This interference reduced panicle number per plant,number of grains per panicle,seed setting rate,and 1000-garins weight.Grain yield reductions were due to decreases inpanicle number per plant,in number of grains per panicle,in seed setting rate,and in1000-garins weight.The competion of weedy rice have no significant effect on plant height,leaf length andwidth,net photosynthesis rate and transpiration rate of cultivated rice.Daily meantemperature,daytime mean temperature,night mean temperature,daily maximum temperatureand daily minimum temperature of treatment of transplanting high density of weedy ricesignificant more than CK.Daily mean humidity,daytime mean humidity,night meanhumidity,daily maximum humidity and daily minimum humidity of treatment oftransplanting high density of weedy rice significant more than CK.5,We conducted pot experiment to study the seedling emergence of weedy rice inNorthern China at different planting depths.It shows that the elongation of mesocotyl andinternode of coleptile plays important roles in the seedling emergence of China weedy rice.Weedy rice elongated the mesocotyl at 3 cm planting depth and elongated the mesocotyl andcoleptile at 5 cm planting depths.The germination dynamics of weedy rice at deep plantingdepth depending on the elongation of mesocotyl and the elongation of coleptile.Weedy rice materials collected in rice field and 16 cultivated rice are used to study themesocotyl elongation characteristics under illumination condition.The results indicate thatweedy rice's mesocotyl elongation characteristics are better than cultivated rice's.Amongcultivated rice,indica rice's mesocotyl elongation characteristics are better than japonicarice's.Although weedy rice's mesocotyll elongation characteristics are better,but there isgreat difference between weedy rice materials.The systematical cluster analysis of mesocotylelongation characteristics reveal that the 109 materials in experiment may divide into longmesocotyl type,short mesocotyl type and intermediate type.57% weedy rice materials belongto long mesocotyl type and intermediate type.Long mesocotyl weedy rice germplasmWR04-6, WR04-7,WR04-8,WR04-24-white,WR04-43,WR04-46 and WR05-6 are screened.Study on dynamic analysis of mesocotyl elongation showed that the activity ofα-amylase andβ-amylase in seed increased,the content of soluble sugar added and the solubleprotein decreased,which provided powerful growth dynamics for the elongation of mesocotyl.Study on the cell wall-bound enzyme activity showed,The ionically bound cell wall proteincontent,POD activity,IAA oxidant enzyme were higher than which were covalently boundcell wall.The ionically bound cell wall protein content,POD activity inhibited the elongationof mesocotyl.Call wall-bound IAA oxidant enzyme to the elongation of mesocotyl was notobvious.The changes of covalently bound cell wall protein content,enzyme activity werecomplex and the relations with the elongation of mesocotyl were not obvious.Study ofinternal hormone indicated,IAA did not have evident action on mesocotyl elongation,GApromoted the elongation of mesocotyl,ABA inhibited it.The results of genetic analysis indicate that the mesocotyl elongation is controlled bytwo additive-dominance-epistatic major genes and polygenes.6,The cold tolerance at seedling period for 100 weedy rice and Akihikari wasindentified.The results showed that much weedy rice has stronger cold tolerance thanAkihikari.The results indicated that protective enzyme activities and soluble organicosmoticum were increased at first and then decreased,lipid peroxidation content was lastingincreased under low temperature treatment at seedling stage.WR03-45 and WR04-35 hadhigher soluble sugar content and soluble proline content,stronger protective enzymeactivities,and lower MDA content.That indicated WR03-45 and WR04-35 had strong coldtolerance at seedling stage.