| Rice(Oryza sativa L.)is a main food resource for more than a half population in the world.Rice breeding plays an important role in ensuring food security.During the life cycle of rice,various kinds of diseases and pests will be encountered.Among them,the brown planthopper(BPH,Nilaparvata lugens Stal)is one of the most destructive pests to rice,which can cause severe yield loss or even extinction of rice.It is the most economic and time-effective strategy to introduce BPH resistance genes into elite rice varieties for genetic improvement.The advance of molecular breeding technology provides a new approach for accelerating the development of new varieties and improving the breeding efficiency.The objectives of this study were to introgress the BPH resistance genes into elite rice varieties through backcrossing,molecular marker assisted positive and negative selection of target genes,and whole genome marker assisted background selection,to develop BPH resistance rice lines.The main results are as follows:1.BPH-resistance genes BPH14 and BPH15 of B5 were successfully introgressed into an elite rice restore line 'Huahui938' by backcrossing and marker-assisted selection(MAS).Three new lines,designed as 'H613002-5-30-10','HB13002-5-31-24' and'HB13002-50-9-7',were finally abtained.These lines stacking homozygous BPH14 and BPH15 had a genetic background recovery percentage from 86.62%to 87.88%of'Huahui938'.BPH bioassays results indicated that the resistance grades of all three breeding lines were 1 or 3,showing resistant or highly resistant to BPH at seedlings.For the hybrids that derived from these improved restorer lines and sterile lines,if the sterile lines carried homozygous BPH14 and BPH15,the derived hybrids also presented resistant to BPH at seedlings;if not,the BPH resistance of the derived hybrids were not improved at seedlings.The randomized block experiment trials in field showed that,the main agronomic traits,grain yield and rice qualities of three new lines were similar to those of the reccurent parent.The main agronomic traits,grain yield and rice qualities of hybrids derived from 'Quan9311A' and improved lines were correspond to those of the control 'Fengliangyou4',and it is expected to develop new hybrid varieties by further multi-point experiments.2.BPH-resistance genes BPH14 and BPH15 were introgressed from the donor'HB13001-14-5' into an elite inbred variety 'Wushansimiao' by backcrossing,target genes positive and negative selections,and whole genome-wide marker-assisted background selection that based on SSR markers distributed on 12 chromosomes,medium-and high-density SNP chips.Five new lines,designed as 'IB17004-7-47','HB17004-7-50','HB17004-7-54','HB17004-7-72' and 'HB17004-7-88' were developed.For these new lines,the introgression fragments were 437.7 kb for BPH14 and 417.6 kb for BPH15,respectively.Except for these two fragments,the residual genetic background of the new lines was identical to that of the recurrent parent,with a genetic background recovery rate of 99.78%.BPH bioassay results indicated that the BPH resistance grades of these five new lines were all 1 at seedlings,showing highly resistant to BPH.The BPH resistance grades of these five new lines were all 3 at adult stage,showing resistant to BPH.Under the same conditions,the recurrent parent'Wushansimiao' showed susceptible to BPH.Besides,the mass of honeydew excretions and the weight gains of the BPHs fed on these five new lines were significantly less than those of the reccurent parent at tillering stage.Three repeats randomized block field trials at Hainan and Wuhan showed that the grain yield,growth duration,main agronomic traits,and grain qualities of these five improved lines were statistically indistinguishable from those of the recurrent parent.Moreover,the growth duration,grain yield and main agronomic traits of hybrids,which derived from these improved lines and different sterile lines,were also consistent with those of the hybrids derived from 'Wushansimiao' and correspongding sterile lines.Several rice qualities of new hybrids were even better than those of the the original hybrids.These results indicated that BPH1 4 and BPH1 5 had been precisely introgressed into the genetic background of 'Wushansimiao' by whole genome marker assisted background selection,which can directionally improve the BPH resistance of the recurrent parent without negative impact the original agronomic traits and rice qualities.At present,the improved line 'HB17004-7-88' has been provided to a commercial seed company as an alternative of 'Wushansimiao' for rice production.It is one of the most precised breeding cases for introgressing two shortest fragments with a highest background recovery through backcrossing and whole genome marker assisted background selection in rice.3.With 'HB13001-14-5' as the donor,several single-segment substitution lines(SSSLs)of Wushansimiao were developed by the whole genome marker assisted background selection system.Each SSSL only carries a single chromosome fragment containing BPH14 or BPH15,which ranges from 428.5 kb to 13.3 Mb.Through analyzing the difference of fragments length,field phenotypes and rice qualities of these SSSLs,it was found that the QTLs in the linked fragments of BPH14 would influence the plant heights and growth duration of these SSSLs.4.BPH-resistance genes BPH14 and BPH15 were also introgressed from the donor'HB13001-14-5' into an elite inbred variety 'Huanghuazhan' by a similar selection system of backcrossing,positive and negative selections of target genes,and whole genome marker assisted background selection.Five new lines,designed as HB17010-180-171-1,HB17010-180-171-39,HB17010-180-171-63,HB17010-180-171-75 and HB17010-180-171-86 were developed.For these new lines,the introgression fragments were 362.7 kb for BPH14 and 1049.4 kb for BPH15,respectively.Except for these two fragments,the residual genetic background of the new lines was nearly identical to that of the recurrent parent,with a genetic background recovery rate of 99.64%.BPH bioassay results indicated that the BPH resistance grades of these five new lines were all grade 1 at seedlings,showing highly resistant to BPH;while the BPH resistance grade of 'Huanghuazhan' was grade 9,showing highly susceptible to BPH.The BPH resistance grades of these five new lines were all grade 1 at adult stage,showing resistant to BPH.Under the same conditions,the the BPH resistance grade of 'Huanghuazhan' was grade 7,showing susceptible to BPH.Besides,the mass of honeydew excretions and the weight gains of the BPHs fed on these five new lines were significantly less than those of the reccurent parent at tillering stage.Field trials in Hainan showed that the plant height of improved lines was siginificant shorter than that of the recurrent parent,and the grain yield,growth period,and other major agronomic traits of improved lines were similar with those of the recurrent parent.Field trails in Wuhan showed that the grain yield,growth period,and all major agronomic traits of five improved lines were similar with those of the recurrent parent.Rice quality analysis results showed that the milling and appeaeance qualities of five improved lines in Hainan were significantlt increased than those of 'Huanghuazhan',and the rice qualities of five improved lines in Wuhan were all similar than those of 'Huanghuazhan'.These results also indicated that BPH14 and BPH15 could be precisely introduced into the genetic background of'Huanghuazhan' by whole genome marker assisted background selection,to improve the BPH resistance of the recurrent parent without negative impact the other traits. |
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