利用SSR分子标记辅助选择构建QPM近等基因系

利用分子标记辅助选择构建QPM近等基因系,以phi057为特异性引物,对90个回交群体各世代进行选择,构建出一批来自不同遗传背景的QPM近等基因系。结果表明,引物phi057在QPM与普通玉米自交系间表现多态性,能准确区分O2O2、O2o2和o2o2这3种基因型。因此,利用微卫星标记引物phi057在QPM与普通自交系杂交、回交世代中进行o2基因的选择是可行的。实验中的大部分材料在回交5～6代后与轮回亲本的农艺性状极为相似并稳定下来。经卡方检验,OO和Oo的分离比例为1∶1,符合孟德尔遗传分离比例。     

玉米O2和Wx基因内及O16基因连锁SSR位点的等位变异研究

以13个o2o2基因型的高赖氨酸玉米自交系、3个o16o16基因型的高赖氨酸玉米自交系、13个wxwx基因型的糯玉米自交系和8个普通玉米自交系为材料,用3个02基因内SSR标记(umc1066、phi057和phi112)、2个与o16基因连锁的SSR标记(umc1141和umc1121)和2个wx基因内SSR标记(phi027和phi061)检测上述材料的基因组DNA,了解3个基因内共7个SSR位点的等位变异情况.结果表明,7个SSR位点均有丰富的等位变异,这些变异可导致o2o2与O2O2基因型、o16o16与O16O16基因型间子粒赖氨酸含量的差异以及wxwx与WxWx基因型间糯性的差异.     

玉米O2和Wx基因内及O16基因连锁SSR位点的等位变异研究

以13个o2o2基因型的高赖氨酸玉米自交系、3个o16o16基因型的高赖氨酸玉米自交系、13个wxwx基因型的糯玉米自交系和8个普通玉米自交系为材料,用3个o2基因内SSR标记(umc1066、phi057和phil12)、2个与o16基因连锁的SSR标记(umc1141和umc1121)和2个wx基因内SSR标记(phi027和phi061)检测上述材料的基因组DNA,了解3个基因内共7个SSR位点的等位变异情况。结果表明,7个SSR位点均有丰富的等位变异,这些变异可导致o2o2与O2O2基因型、o16o16与O16O16基因型间子粒赖氨酸含量的差异以及wxwx与WxWx基因型间糯性的差异。     

小麦D2型细胞质雄性不育恢复基因近等基因系筛选和遗传背景的分子检测

通过连续回交和单株（系）跟踪选择，培育成小麦D^2型细胞质雄性不育系msD^2-CA8057恢复基因的近等基因系（BC6F1）材料。应用SSR分子标记技术，对9个恢复基因近等基因系单株及不育系msD^2—CA8057和恢复系遗4060的遗传背景进行了比较检测分析，结果表明，所检测到的遗传多样性集中于近等基因系与恢复系之间，而9个近等基因系单株之间及其与不育系之间的遗传背景具有很高的一致性；近等基因系C3只含一个主效恢复基因D^2Rf1，该单株的自交和回交群体可望用于对该基因的精细定位。     

玉米不同回交世代DH系遗传分析研究

[目的]研究不同回交世代DH系遗传分离规律。[方法]以"A619Ht3×辽3162"构建回交群体BC1F1和BC5F1,利用高频诱导系诱导加倍形成BC1F1和BC5F1的DH系,以DH系为材料,通过比较不同回交世代的DH系和父母本的农艺性状,对其做出评价,同时利用SSR分子标记分析DH系的遗传分离特性。[结果]DH系间株高、穗位高、穗长、穗粗、穗行数、行粒数等农艺性状存在较大的遗传变异,回交群体DH系中没有出现明显偏分离比例,通过χ^2检测,未达到显著水平。[结论]不同回交世代所创制的DH系的主要农艺性状差异均达到极显著水平,回交群体DH系中不存在明显的偏分离现象。     

小麦抗条锈病基因Yr2的SSR标记

为了利用SSR技术寻找与小麦抗务锈病基因Yr2紧密连锁的分子标记,以近等基因系Taichung29*6／HeinesⅦ与感病的背景亲本Taichung29构建F2分离群体,进行了F2单株苗期抗条锈病鉴定。抗性分析表明,近等基因系Taichung29*6／HeinesⅦ中的抗条锈病基因是由单基因控制的。进一步用7B染色体上的45对SSR引物对抗、感亲本及171株F2分离群体进行SSR分析,筛选出一个与小麦抗条锈病基因Yr2紧密连锁的SSR标记WMC364-207 bp／201 bp。通过最大似然法计算,该标记与Yr2基因之间的遗传距离为5.6 cM。     

水稻果皮色泽近等基因系的构建及近等性评价

 以紫香糯和春江糯2号为亲本,利用F2、BC1F1和F3分离群体对果皮色泽性状进行遗传分析,并构建了7对果皮色泽近等基因系。遗传分析结果表明紫香糯果皮的色泽性状由两对互补基因控制。对7对近等基因系进行的性状相似性和遗传背景的SSR分子标记检测结果表明,近等基因系间在农艺性状上除了千粒重外,其他性状差异均不显著。利用34对亲本间多态性SSR分子标记,发现5对黑、白近等基因系仅在目标基因区段检测到了多态性标记,近等性比较理想;2对黑、褐近等基因系除了目标区段外,还分别在第11、12染色体检测到了多态性标记,近等性较差。     

玉米不育系回交转育群体背景选择效果的研究

以玉米细胞质不育系cms-合344为供体亲本、辐63018为轮回亲本,构建BC_1和BC_2群体,研究利用SSR标记进行遗传背景选择加速回交转育不育系的效果。选用两亲本间多态性好的并覆盖玉米10条染色体的60个SSR标记进行轮回亲本的遗传背景分析。结果表明,对两群体遗传背景回复率分析,86株BC_1群体背景回复率平均值为74.41%,63株BC_2群体背景回复率平均值为87.36%,BC_1群体表型与分子标记辅助选择相似度均较高的株系有9株,BC_2有8株。对两群体进行不同标记数目分析,两群体中使用40个标记与总数60个标记所计算的背景回复率基本相同,相关系数分别达到0.96和0.95以上。     

玉米胚乳突变体Wrk1基因定位及候选基因预测

Wrkl是在EMS诱导群体中分离得到的玉米胚乳显性突变基因.Wrk1突变体玉米胚乳严重皱缩,导致玉米子粒的千粒重降低30％～50％.研究利用B73为回交亲本构建BC1分离群体,通过9 800个单株把Wrk1基因定位在开发的SSR标记Mssr1824和Mssr2042之间,二者之间的物理距离约1.2 Mb.在此基础上,另外构建一个以M017为回交亲本的BC1群体,通过11280个单株把Wrk1基因定位在开发的SSR标记Mssr1916.2和Mssr1838之间,二者之间的物理距离约185 kb.通过基因预测和注释,发现在该区域内有7个候选基因,为Wrk1基因的最终克隆奠定了基础.     

玉米花期性状的主效SSR标记筛选

根据国内外已发表的与玉米花期相关性状主效QTL(贡献率10%)连锁的SSR标记中,选取30对SSR标记引物,筛选玉米花期性状的主效SSR标记。选用花期不同的玉米自交系P014、P037、E1312为亲本,分别组配得到两个杂交后代F1(P014×E1312)和F1(P037×E1312),F1经自交获得两个F2(P014×E1312)、F2(P037×E1312)群体为试验材料。利用亲本、F1代对30对引物进行筛选,获得的特异性引物再通过F2群体单株花期性状与单株SSR标记的符合度和准确率验证,筛选出符合率大于50%的主效标记。结果表明,bnlg1505、bnlg1666、umc1663、bnlg128为玉米花期性状的主效SSR标记,其中,标记bnlg1505适用于筛选抽雄期晚、散粉期晚、吐丝期晚的材料,筛选准确率分别为56.5%、65%、60%;标记bnlg1666适宜用于筛选散粉期早、吐丝期早的材料,筛选准确率分别为65%、57.5%;标记umc1663和bnlg128适用于筛选散粉期早的材料,筛选准确率为68%和61.5%。     

玉米回交后代群体中供体基因组成分分析

以郑58为受体亲本,昌7-2为供体亲本,通过杂交、回交和79对亲本间有多态的SSR标记,分析BC₂F₁和BC₃F₁世代供体的基因组成分。结果表明：BC₂F₁世代单株内的供体染色体片段数平均为11.4个,BC₃F₁世代为4.8个,从BC₂F₁到BC₃F₁单株内的供体染色体片段数减少了57.6%;BC₂F₁世代单株内的供体染色体片段长度平均为99.3 cM,BC₃F₁世代为87.1 cM,BC₃F₁较BC₂F₁减少了12.3%;BC₂F₁世代单株内的供体基因组大小平均为1 132.8 cM,BC3F1世代为421.4 cM,BC₃F₁较BC₂F₁减少了62.8%。     

基于SSR标记的玉米丝黑穗病抗性的关联分析

选取玉米染色体上的2.09、3.04、3.05 3个区段的55个SSR标记对16份抗感玉米丝黑穗病的玉米自交系基因组DNA进行扩增,并对SSR分子标记基因型与丝黑穗发病率进行关联分析。结果表明,40对SSR引物多态性较好,检测出的等位基因数为2～5个,平均为3个,多态性信息量(PIC)为0.180～0.765,平均为0.562。初步确定与玉米丝黑穗病相关程度达显著以上的标记14个,占多态性标记的35%。其中,标记umc2077和umc1525与玉米丝黑穗抗性相关呈极显著水平,可进行辅助选择研究。     

玉米矮花叶病抗病基因Rscmv1的精细定位

以感病亲本Mo17为轮回亲本、抗病亲本四一为供体亲本,构建近等基因系,对抗病基因Rscmv1进行精细定位。结果表明,在自交系四一中定位了两个抗病基因Rscmv1和Rscmv2,其中Rscmv1是抗源中普遍存在的主要抗病基因。以选育的近等基因系BC4F3、BC4F4和BC4F5为定位群体,在抗病基因区域内开发了9个有多态性的BAC-SSR标记,将Rscmv1定位在BAC-SSR标记A5-1和B2-1之间,其遗传距离分别为0.3 cM和0.6 cM,2个标记之间的物理距离为1.38 Mb。     

Introgression of Gene for Non-Pollen Type Thermo-Sensitive Genic Male Sterility to Thai Rice Cultivars

For the two-line hybrid rice system, pol en sterility is regulated by recessive gene that responds to temperature. The recessive gene controlling thermo-sensitive genetic male sterility （TGMS） is expressed when the plants are grown in conditions with higher or lower critical temperatures. To transfer tgms gene（s） control ing TGMS to Thai rice cultivars by backcross breeding method, a male sterile line was used as a donor parent while Thai rice cultivars ChaiNat 1, PathumThani 1, and SuphanBuri 1 were used as recurrent parents. The BC2F2 lines were developed from backcrossing and selfing. Moreover, the simple sequence repeat （SSR） markers were developed for identifying tgms gene and the linked marker was used for assisting selection in backcrossing. The identification lines were confirmed by pol en observation. The results showed the success of introgression of the tgms gene into Thai rice cultivars. These lines will be tested for combining ability and used as female parent in hybrid rice production in Thailand.     

Biofortification of sweet corn hybrids for provitamin-A,lysine and tryptophan using molecular breeding

Traditional sweet corn is poor in provitamin-A, lysine and tryptophan, deficiency of which causes serious health problems. Here, parental lines of two shrunken2 (sh2) -based sweet corn hybrids viz., ASKH-1 and ASKH-2 were targeted for introgression of crtRB1 and opaque2 (o2) genes through marker-assisted backcross breeding. Gene-based markers; umc1066 (SSR) and 3′TE-InDel were utilized for foreground selection of o2 and crtRB1, respectively in BC₁F₁, BC₂F₁ and BC₂F₂ generations. Background selection employing 102–113 polymorphic SSRs led to >90% recovery of recurrent parent genome. Reconstituted hybrids recorded high mean provitamin-A (18.98 μg/g) with a maximum of 7.7-fold increase over original hybrids (3.12 μg/g). High mean lysine (0.39%) and tryptophan (0.10%) with an average enhancement of 1.71- and 1.79-fold, respectively was recorded among reconstituted hybrids over original versions (lysine: 0.23%, tryptophan: 0.06%). Improved hybrids exhibited high phenotypic resemblance with their original hybrids. The average cob yield (11.82 t/ha) and brix (17.66%) of improved hybrids was at par with their original versions (cob yield: 11.27 t/ha, brix: 17.04%). These biofortified sweet corn hybrids rich in provitamin-A, lysine and tryptophan hold immense significance as multinutrient-rich balanced food. This is the first report to stack sh2, crtRB1 and o2 genes to improve nutritional quality in sweet corn.     

Quality Protein Maize: Overcoming the Hurdles

SUMMARY

Quality Protein Maize (QPM), a nutritionally enhanced maize, was developed by researchers from CIMMYT using too genetic systems–opaque-2 and genetic modifiers. The use of these two genetic systems overcame the highly complex problems that were inherent in the original soft endosperm opaques. This review describes the ever-evolving breeding options and strategies for the development of QPM with examples from the CIMMYT maize program, where much of the research and practical breeding work has been done. The soft endosperm opaque-2 materials developed earlier had poor agronomic performances and lacked producer and consumer acceptance. To overcome these constraints, subsequent research explored various options, with and without high lysine mutants. Like other institutions, CIMMYT researchers tried and critically examined the merits and demerits of different strategies. Of all the strategies available, the selection for modified kernels in which CIMMYT scientists had gained information, experience, and confidence seemed viable. To implement this strategy, modified opaque-2 donor stocks were built and were subsequently used for expanding the QPM developmental efforts. A large volume of QPM germplasm was developed using different breeding options, which were later merged and reorganized into a fixed number of pools and populations to permit working in homozygous opaque-2 genetic backgrounds. The development of QPM hybrids was the next turning point in the mid-80s. During the QPM developmental process, serious problems inherent in the opaques were circumvented and since then, rapid progress has been made. There is a renewed interest in QPM and several countries have recently released QPM varieties and hybrids. To further accelerate the QPM developmental process, to enhance its popularity amongst nations and its farmers, and to meet future challenges, innovative ideas and the tools of biotechnology will be needed.