| In this study, Shuhui527and Minghui86, which were two widely used eliteindica restorers in China, were used as the recurrent parents, Gui99, R2004, lemont andYunhui72as donors for developing eight BC2F2backcrossing introgression populations.These populations were imposed critical screening for yield and lodging resistance (LR)traits, through field estimation of yield traits and morphology traits of culms combiningwith the determination of culm bending force using dynamometer, from which eight BC2F4selected backcrossing introgression populations with high yield and lodging resistancewere developed. The progeny of the BC2F4backcrossing populations and their parentswere tested for yield and LR traits in2008and2009in Hefei. The identification ofgenotyping was conducted in the National Key Facility for Crop Gene Resources andGenetic Improvement/Institute of Crop Science in Chinese Academy of AgriculturalSciences (CAAS) in2009. Five yield traits (filled-grain number per panicle, spikelets perpanicle, spikelet fertility, thousand grain weight and theoretical yield) and five LR traits(stem diameter, wall thickness, flexural strength of the second internode, flexural strengthof the third internode and lodging index) were used for phenotypic and genotypic analysis.The analysis included the selection effect analysis of yield and LR, correlation analysis ofyield and LR traits, QTL mapping and effect analysis of yield traits and LR traits, thegenetic overlap analysis of yield and LR traits. The results in this study provide importantinformation for the application of favourable gene or QTLs in high yield and LR breeding,the direct and indirect use of progenies, and the simultaneous improvement of yield andLR traits. The main results are as follows:1. The effectiveness of the selection for yield and lodging resistance traitsThe eight BC2F4backcrossing populations in the genetic background of Shuhui527andMinghui86were imposed critical selections for yield and LR traits, from which a total of190introgression lines (ILs) were selected. Progeny testing allowed the identification of150(78.9%) and154(81.1%) lines which showed better yield performances than therecurrent parents. Of which,140lines had higher yield than the recurrent parents in two years, accounted for75.3%of the ILs. Furthermore,101lines with10%stably increasedyield in two years accounted for a lager portion (53.2%), the selected superior lines weremainly determined by genotypes, thus demonstrated the effectiveness of the selection.There was a certain difference in the effectiveness of the yield selection between thepopulations of different recurrent parents, the four populations with Shuhui527as therecurrent parent had better performances.In2008and2009, there were128and131lines which had lower lodging index thanthe recurrent parent, account for67.4%and68.9%respectively. Of which,108lines hadlower lodging index than the recurrent parents in two years, accounted for56.8%of the ILs.Furthermore,63lines with5%decreased lodging index in two years accounted for33.2%.In general, the ILs showed the consistent trend of the lodging index, they were mainlydetermined by genotypes, thus demonstrated the effectiveness of the selection. There weredifferences in the effectiveness of the selection among different populations. There was ahigh percentage of ILs in527-99and527-72populations which had lower lodging index intwo years with good and stable performances.Compared with the recurrent parents,82ILs had higher yield and low lodging index,accounted for43.2%. These findings indicated that it is feasible to make improvement ofyield and LR traits simultaneously, thus achieve high yield and LR together. Therefore, ourresults revealed an efficient breeding strategy using selected backcross introgression linesfor improving yield and LR in rice.The donor parent Gui99play an important role in the improvement for yield traits ofthe recurrent parents while the donor parent R2004contributed more in the improvementof LR traits, they could be used as materials in the practice breeding.Take the yield components of superior lines with stable performances in both yield andLR into consideration, if high yield and LR is to achieve, an ideal grain structure is needed,the general spikelets per panicle is about200, filled-grain number with160-180grains isadvisable.2. Correlation between yield and lodging resistance related traitsThe key points in high yield breeding could be conducted to improve the tilleringability and spikelet fertility, to ensure certain filled-grain number per panicle, maintaininghigh thousand grain weight, rather than pursuit the long and huge panicle. On the basis ofenough panicle number and large panicle, the high or low spikelet fertility is the mostimportant point. Panicle number, filled-grain number per panicle, and spikelet fertility should be considered, especially when the high yield and lodging resistance were set as thebreeding goal.In order to improve the lodging resistance of rice, stem diameter, wall thickness andthe number of internodes should be increased, the culm type should be improved, thusimprove the lodging resistance.During the breeding process of developing dwarf, high yield and lodging resistancevarieties, the number of internodes, stem diameter and wall thickness can be used as animportant index. Furthermore, the determination of stem bending force or thrust is alsoconsidered to evaluate the lodging resistance of rice.3. The main effect QTL and its applicationThe results of QTL mapping showed that many QTLs were identified at the significantlevel P<0.01. These identified QTLs were explained over30%of the phenotypic variationswith large additive effect and expressed stably in two years. It is indicated that these lociare important for the improvement of yield and lodging resistance traits, such as qGN10.1,qGN7.1, qGN1.2, qGN1.3, qGN11.4and qGN2.1controlling the filled-grain number,qSN2.1, qSN1.3, qSN1.4, qSN1.5and qSN2.4controlling spikelets per panicle, qSF10.1,qSF5.1, qSF1.1, qSF3.4, qSF4.1, qSF5.3, qSF6.2, qSF1.3and qSF1.4controlling spikeletfertility, qGW2.1, qGW7.1, qGW12.1, qGW1.5, qGW1.6, qGW6.4and qGW7.5controllingthousand grain weight, qGY3.1controlling grain yield, qSD2.2, qSD1.1, qSD1.6, qSD1.3,qSD1.4, qSD2.8and qSD1.9controlling stem diameter, qCT2.2, qCT2.1, qCT7.3, qCT1.3and qCT1.4controlling wall thickness, qCS7.1, qCS9.1, qCS1.3, qCS1.4and qCS1.5controlling flexural strength of the second internode, qCS â…¢7.1,qCS â…¢9.1,qCS â…¢12.4,qCS â…¢1.2, qCS â…¢1.3, qCS â…¢1.4and qCS â…¢2.1controlling flexural strength of thethird internode, qLI1.2and qLI7.2controlling lodging index. The introgressions of thedonor at some loci have greatly improved some index of yield and lodging resistance, butled to a decline in other major yield components. Therefore, the correlations among themain traits should be taken into account when some favorable genes/QTLs would beintrogressed.4. The genetic overlap of yield and lodging resistance traitsThere were genetic overlaps among yield traits within the same population, betweenyield and LR traits, among the donors in the same genetic background. These geneticoverlaps provided useful information for the simultaneous improvement of yield and lodging resistance traits. For example, three adjacent main effect QTL, qGN1.2(qSN1.3qCS1.3qCSIII1.2), qGN1.3(qSN1.4qCS1.4qCSIII1.3) and qGN1.4(qSN1.5qCS1.5qCSIII1.4) which were detected on the chromosome1in the527-72population, hadnegative additive effect on filled-grain number, spikelets per panicle, flexural strength ofthe second internode and flexural strength of the third internode. The favorable alleles werefrom Yunhui72, which contributed to the increased filled-grain number, spikelets perpanicle, flexural strength of the second internode and flexural strength of the thirdinternode. These QTLs could be applied in the marker-assisted selection (MAS), thus playan important role in the improvement of high yield and LR and progeny selection.To a certain extent, several pleiotropic QTLs were unfavorable for the improvementof different traits simultaneously, so the strategy should be flexible according to differentmaterials and breeding goals and critical selection is needed, thus make good advantage ofthe effects of these QTLs and avoid negative effects. In addition, the expression of thesame QTL is different in different donors under the same genetic background. During thebreeding process, adequate evaluation of the parent is needed. Then, we should get tounderstand the characteristics of the expressions of those favorable genes/QTLs and theirinteractions with the environment in order to make good advantage of them. |
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