| Improvement of grain quality and yield has become one of the most important goals inrice breeding programs. Grain shape related traits and 1000-grain weight have been shownto be quantitatively inherited. Therefore, the use of marker-assisted selection (MAS) mayprovide a more efficient approach for improving these quality traits than classical breedingalone. MAS can be carried out by following five steps: 1. mapping major non-environment-specific loci that can be repeatedly detected in different populations; 2. constructingchromosome substitution segment lines carrying a single donor segment or near isogeniclines covering the whole genome; 3. dissecting target QTLs into single Mendelian factorsand precisely mapping, evaluating the feasibility of MAS by QTL pyramiding; 4.constructing phenotypic database for breeding by molecular technology; 5. transferring orintrogressing, and combinating multiple desirable QTLs. However, most of studies on ricegrain quality and yield were conducted in a single environment or using a single population,the stability of the resultant QTLs could not be evaluated. This characteristic is critical fordetermining the utility of a QTL for MAS. In the present study, the stability of QTLsaffecting grain length, grain width, grain length width ratio and 1000-seed weight wereanalyzed using different populations across different environments. The main conclusionswere as follows:1. Sixteen main effect QTLs were resolved using IR36/Nekken2 RIL population in twoenvironments. The numbers of QTLs for grain length, grain width, grain length width ratioand 1000-grain weight were 3, 3, 3, and 6, respectively. The stable QTLs were qGL-3qGW-5, qGW-6, qLWR-5, and qTGW-3, whose averge PVEs were 17.60ï¼…and 16.10ï¼…,7.85ï¼…, 9.36ï¼…, and 8.30ï¼…, with average LOD scores of 3.94, 4.35, 3.16, 2.25 and 2.14,respectively.2. A total of thirty nine main effect QTLs were detected for grain length, grain width, grainlength width ratio and 1000-grain weight in the Nipponbare/Kasalath//Nipponbare BILpopulation across three environments, qGL-2, qGW-2-1, qGW-5, qLWR-5 and qTGW-2 were repeatedly detected in three environments. Their averge PVEs were 17.60ï¼…16.10ï¼…,7.85ï¼…, 9.36ï¼…, and 8.30ï¼…, with average LOD scores of 5.43, 3.06, 6.50, 3.68 and 4.26,respectively. Further stability analysis was conducted using CSSLs with Nipponbare as thegenetic background and Kasalath as the donor in three environments. The result showedthat significant difference of phenotypic values existed between the recurrent parent,Nipponbare, and the CSSL NK50 harboring qGL-2, qGW-2-1 and qTGW-2-1 alleles.Compared to Nipponbare, NK50 had longer, narrower, and lighter grains. The four CSSLsharboring qGW-5 allele, including NK22, NK32, NK38 and NK50, all had markedlydecreased grain width across three environments, indicating the effects of the allele weresignificant and stable.3. Thirty four main effect QTLs were detected in the Koshihikari/Kasalath//KoshihikariBIL population across three environments, including 9 QTLs controlling grain length, 12controlling grain width and 13 controlling grain length width ratio, qGL-5, qGL-6, qGL-7,qGW-2-2, qGW-3-1, qGW-5 and qLWR-5 were expressed stably in three environments.Their averge PVEs were 8.81ï¼…, 9.29ï¼…, 9.76ï¼…, 8.65ï¼…, 8.77ï¼…, 26.6ï¼…and 39.18ï¼…, withaverage LOD scores of 3.89, 4.42, 3.93, 4.76, 5.40, 13.49 and 18.57, respectively.Significant difference of phenotypic values was observed between the recurrent parent,Koshihikari, and the CSSL KK12 harboring qGL-5 allele across three environments. Thesame case was for the two CSSLs harboring qGL-6 allele, namely KK17 and KK18, as wellas the two CSSLs KK12 and KK14 harboring qLWR-5 allele.4. A total of six QTLs controlling rice grain length, five QTLs controlling rice grain width,eight QTLs controlling rice grain length width ratio were detected using theSasanishiki/Habataki//Sasanishiki///Sasanishiki BIL population in all three environments.QTL qGL-12 for grain length was detected only in two of the three environments, Nanjingand Lianyungang, in 2006, with an average PVE of 8.80ï¼…and an average LOD score of2.46. QTLs qGW-3-2 and qGW-12 were identified in two environments of Nanjing in twosuccessive years. Only qLWR-3 was repeatedly detected in all three environments Thesethree QTL had average PVEs of 16.45ï¼…, 12.40ï¼…and 21.40ï¼…, and average LOD scores of5.10, 3.91 and 4.93, respectively.In conclusion, a total of 14 QTLs for grain shape relevant traits and 1000-grain weight, including qGL-2, qGL-3, qGL-5, qGL-6, qGL-7, qGW-2-1, qGW-2-2, qGW-3-1, qGW-5,qGW-6, qLWR-3, qLWR-5, qTGW-2, qTGW-3, were detected in different mappingpopulation across different environments. Moreover, a QTL cluster for grain width andgrain shape was located on chromosome 5 based on different populations, and another QTLcluster controlling grain length, grain wide and 1000-grain weight was detected onchromosome 2 in Nipponbare/Kasalath//Nipponbare BILs in different environments. Theseresults will provide useful information for elite rice breeding by MAS. |
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