A Study On Heredity And Cold-resistant Capabilities Of The Founder Parent Strains Of Japonica Rice In Cold Regions Of Heilongjiang

Rice is one of the most important food crops and its production has a veryimportant position in food security. The new varieties played an important role in riceproduction. Here we summarized the experience and lesson of the past in ricebreeding; traced the pedigree of cultivated varieties and founder parent in depth, andprovided instructive information and reference for designing the technical routerationally in breeding. In this study, we used226cultivated Japonica rice varietiesauthorized in different times from cold area in Heilongjiang province, which wereinvestigated in the origins and biological evolution, and made clear the founder parentof cold area, analyzed evolving trend of important agronomic traits, and then weanalyzed the genetic difference of51main cultivated varieties of rice including thefounder parent in1990s by using the Simple Sequence Repeats(SSR), all the resultsreveal the genetic difference and relationship between founder parent of Japonica ricein cold area and the progeny. At the same time, We also measured and characterizedcold-resistant capabilities of the cultivated varieties in different developmental stagesincluding in seedling，tillering, boot and mature stages, Besides, we analyzed therelationship of cold tolerance in different stage and molecular marker. We hoped thatall these result can provide effective theoretical bases for rationally using the founderparent and promoting the breeding efficiency, and which could pave the way formolecular marker-assisted breeding and gene locating and cloning in cold tolerance ofrice.The main results were as follows:1. We collected and tracked the pedigree of226main cultivated varieties in coldregion of Heilongjiang. Our results defined Shishoubaimao and Xiayi、Tengxi-138、Fushiguang、Nonglin-11、Xiabei、Shangyu-397、Wuyoudao-1as the founder parentstrains in cold region of Heilongjiang. We further analyzed the nucleus andcytoplasmic contribution values of these varieties,7varieties’ nucleus contributionvalues were more than5. They are Shishoubaimao, Xiayi, Tengxi138, Fushiguang,Nonglin11, Xjiabei and Shangyu397. Of them, the nucleus contribution value ofShishoubaimao reached18.85, which was much higher than others. This suggestedShishoubaimao is the most important founder parent strain of cultivated varieties inHeilongjiang.2. We tracked the laws of changes and development of several important agronomic traits of226founder parent varieties. Applying principal component analysis approach to estimatecontribution of6founder parent varieties on the important agronomic traits, we found the mostcontributed variety was Shishoubaimao. The variety highly contributed to grain numberper panicle, its feature value was3.02and contribution rate was50.38%. The secondcontributed trait by Shishoubaimao was1000kernel weight, which contribution ratereached30.69%. The third one was grain weight per plant. Its contribution rate is14.62%. The second most contributed founder parent strain is Xiayi, whichcontribution rate on was1000kernel weight48.02%, on plant height was28.51%andon seed setting rate was15.77%.the accumulative contribution rate by Shishoubaimaoand Xiayi reached95.69%and92.30%respectively. We also analyzed thediversification trends of several important agronomic traits of the founder parent strainsand their derivative strains derived from different breeding history. The overall trends of plantheight changed towards lowers. Plant height reached highest level in1950s; thendecreased a little bite in1960s; followed by a significant decrease during1970s and1970s. After1980s, changes on plant height of the stains were comparatively lesssignificant. On the other hands, the number of the tillers was increasing successively.Form1950s to1970s, the number of the tillers slightly increased,10more thanprevious one. After1980s, the number of the tillers increased significantly. Thepanicle length of rice in1960s was significantly lower than the others, while increasedgradually through1970s to1990s and reached the maxim value in1990s. After2000the panicle length was slightly decreased. Ear weights have similar trends like thepanicle length before2000. However， ear weights increased significantly after2000than others. Grain weight per spike reached maxim value in1970s while slightlydecreasing after that. The lowest number of primary branches occurred in1950s whilereached highest number in1980s. The number of secondary branches changedsimilarly like the number of primary branches. It increased significantly and hadhighest number in1970s and significant lowest ones after2000. Setting percentagewas low in1950s and1960s and gradually increased in1990s while reached highestlevel after2000.1000kernel weight was continually increasing from1950s to2000and the increment was significant.3. We designed50pairs of SSR primers to detect genetics diversities of150SSRmarkers in51main cultivated varieties of rice in1990s. Data were then analyzed byUPGMA and principal coordinate analysis (PCO). We detected number of changedbands ranged from2to6with3as mean. The average primer PCI is0.3655, changed from0.0725to0.6845. According to the genetic similarity factors of0.6, the51testing samples could be classified into4groups. Group1is Wuyoudao1and theirderivative strains. Group2is Fushiguang and their derivative strains. Group3is Tengxi138and their derivative strains. Group2is Shangyu397and their derivative strains. PCO analysisshowed that the for founder parent strains and their derivative strains were genetically diversified.We also detected39SSR markers as rare alleles. Of them, only3were detected in founder parentstrains. Moreover, experimental verification of SSR and PCO analysis is highly consistent with thepedigree records which double confirmed the reliability of our experiment. Taken together, ourresult suggested that the genetic improvement of main cultivated varieties in cold region ofHeilongjiang in the past20years was performed on the basis of a limited range of geneticbackground. The derivative strains are genetically closed to their founder parent strains.4. In this study, we analyzed morphological characters of226cultivated Japonicarice varieties in cold-resistant capabilities. Results indicated that, in seedling stage, wedetected the average seedling death rate was35.2%with a wild range from3%to8%.In tillering stage, The average seedling emergence rate was69.2%, ranged from21.2%to93.5%with variation coefficient of18.6%. In boot stage, we found theaverage relative setting percentage was70.5%changed from2.1%-94.6%withvariation coefficient of15.7%. In mature stage, the average relative ear weights ofsignal plant was66.5%，ranged18.2%to93.7%. Its variation coefficient was25.7%5. We identified422alleles by using102SSR primers that having polymorphismbetween varieties. The result of clustering analysis of SSR showed that the similaritiesfrom61%to94%. It suggested that the testing rice varieties were genetically close.Combining the similarities of SSR data and phylogenetic tree, we classified thevarieties into2groups, the seedling death rate were lower or higher than35%inseedling stage under cold treatment, the seedling emergence rate s were lower orhigher than69%in tillering stage treated by cold water, the relative setting percentagewere lower or higher than70%in boot stage treated by cold water and the relative earweights of signal plant were lower or higher than66%in mature stage treated by coldwater.6. We also carried out an association analysis between cold-resistant traits andSSR markers, results indicated that5markers relative to cold tolerance in seedingwere detected (RM225-160, RM230-260, RM488-190, RM249-130and RM551-200).RM488-190and RM551-200were correlated with high seedling death rate (>35%) inseedling stage which related coefficients were0.23and0.16respectively. RM225-160, RM230-260and RM249-130were highly associated with low seedling death rate (<35%), which related coefficients were0.37,0.45and0.13respectively. RM498-220,RM230-260, RM1337-210and RM235-110were correlated with seedling emergencerate to low seedling emergence rate (<69%, related coefficients=-0.27), whileRM498-220, RM230-260and RM1337-210were related to high seedling emergencerate (>69%, related coefficients=-0.55,-0.37, and-0.35). RM498-220,RM263-180,RM587-240, RM264-200, RM242-235and RM20-150were associatedwith relative setting percentage in boot stage under cold water treatment. Among them,RM587-240and RM20-150were related to low setting percentage (<70%, relatedcoefficients=-0.24and-0.31), while RM498-220, RM263-180, RM264-200andRM242-235were related to high setting percentage (>70%, related coefficients=0.37,0.32,0.21and0.48). RM230-260, RM246-120, RM1267-170and RM410-190were associated with relative ear weights of signal plant in mature stage under coldwater treatment. RM1267-170was related to low ear weights of signal plant (<66%,related coefficients=--0.28), while RM230-260, RM246-120and RM410-190wererelated to high ear weights of signal plant (>66%, related coefficients=0.33,0.25and0.26).