QTL mapping of yield-related traits in the wheat germplasm 3228

The new wheat germplasm 3228, a putative derivative of tetraploid Agropyron cristatum Z559 and the common wheat Fukuhokomugi, has superior features in yield-related traits, particularly in spike morphological traits, such as large spike and superior grain number. To identify favorable alleles of these traits in 3228, 237 F_2:3 families were developed from the cross 3228/Jing 4839. A genetic map was constructed using 179 polymorphic SSR and EST-SSR markers. A total of 76 QTL controlling spike number per plant (SNP), spike length (SL), spikelet number per spike (SNS), floret number per spikelet (FNS), grain number per spike (GNS) and thousand-grain weight (TGW) were detected on 16 chromosomes. Each QTL explained 1.24–27.01% of the phenotypic variation, and 9 QTL (28.95%) were detected in two or all environments. Additive effects of 45 QTL were positive with 3228 alleles increasing the QTL effects, 31 QTL had negative effects indicating positive contributions from Jing 4839. Three important clusters involving all traits were located on chromosomes 5A, 6A and 4B, and several co-located QTL were also found. Most of the QTL detected on the three chromosome regions could contribute to the use of 3228 in breeding for grain yield improvement.     

YM型小麦温敏雄性不育系不育基因的QTL定位

YM型小麦温敏雄性不育系的不育基因被定位在1Bs染色体片段上, 但已发现的相邻分子标记与该基因的遗传距离较大, 达10 cM以上。为寻找与该基因连锁更紧密的分子标记, 以YM型温敏雄性不育系ATM3314与恢复系中国春杂交的F₂代200株为作图群体, 从1Bs的22个SSR引物中筛选出5个在亲本和F₂代中分离的SSR引物, 构建了1个包含5个标记的1Bs局部遗传连锁图谱。结合F₂代个体的育性调查, 采用复合区间作图法在YM型温敏雄性不育系的1Bs染色体上检测到不育基因的1个主效QTLrfv1-1和1个微效QTLrfv1-2。rfv1-1位于SSR标记Xgwm18和Xwmc406之间, 与两标记的遗传距离分别为6.0 cM和4.6 cM, LOD值为8.80, 加性效应23.87, 显性效应10.44, 可解释表型变异的23.91%; rfv1-2位于Xwmc406和Xbarc8之间, 与两标记的遗传距离分别为4.0 cM和3.4 cM, LOD值为3.10, 加性效应17.59, 显性效应5.99, 可解释表型变异的7.78%。本研究初步定位了YM型小麦温敏雄性不育系1Bs染色体片段上不育基因的QTL, 为进一步准确定位该基因奠定了基础。     

小麦抗白粉病新基因的AFLP和SSR标记及其染色体定位

M53 (YAV2/TEZ//Ae.squarrosa 249) 是硬粒小麦与粗山羊草的双二倍体合成种,携带一个抗白粉病新基因,暂命名为Pm-M53,该基因对北京地区白粉病优势生理小种15号表现免疫抗性。本研究利用来源于杂交组合M53/宛7107的一个F₂群体,在苗期采用白粉病15号小种（Blumeria graminis f. sp. tritici）接种,抗病反应型鉴定表明,抗感比例符合3∶1,说明其抗性受显性单基因控制;对部分F₂植株的F₃株系的抗病鉴定进一步证明了F₂鉴定的可靠性;利用AFLP和SSR标记技术结合F₂分离群体对目的基因进行了遗传作图,将目的基因定位在5D染色体的长臂上。其中AFLP标记P16M16_-109(Apm109)和P5M16_-161(Apm161)与目的基因的遗传距离分别为1.0和3.0 cM。SSR标记Xwmc289b、Xgwm583和Xgwm292与目的基因的遗传距离分别为20.0、33.0和24.0 cM。这些标记位于目的基因的两侧。利用中国春遗传背景的缺-四体和双端体结合AFLP标记Apm109确证了SSR标记定位的可靠性,进一步证明该基因是一个新的抗白粉病基因。     

Cytological and microsatellite mapping of mutant genes for spherical grain and compact spikes in durum wheat

Two mutants for sphaerococcoid seed (MA 16219) and compact spike (MA 17648) were isolated from M₃ progeny of durum wheat cultivar, Altaiskaya Niva, mutagenized with chemical mutagens. The chromosomal locations of the genes involved were determined by the use of a complete set of D-genome disomic substitutions in durum cultivar, Langdon. The gene for sphaerococcoid grain, s ¹⁶²¹⁹ , was allelic to S2, located in the centromeric region of chromosome 3B in hexaploid wheat. The gene for compact spike, C ¹⁷⁶⁴⁸ , was located on chromosome 5AL distal to the Q locus. Using microsatellite markers, C ¹⁷⁶⁴⁸ and awn inhibitor B1 were located in the F₂ of LD222 × MA17648. The gene order was Xbarc319—C ¹⁷⁶⁴⁸ —Xgwm179—Xgwm126—Xgwm291—B1.     

小麦品系M8003-5抗条锈病基因遗传分析和分子作图

为了利用小麦抗条锈病品系M8003-5中的抗病基因,用当前7个流行的条锈菌生理小种对小麦品系M8003-5的抗条锈性进行了鉴定,发现该品种对当前的各优势小种均有良好抗性。在温室内以病菌小种Su11-4对M8003-5在进行苗期抗条锈性鉴定和遗传分析,初步确定M8003-5对Su11-4的抗性由1对显性基因控制,位于7DS上的SSR标记Xbarc5、Xwmc463、Xwmc405、Xbarc126、Xgwm295、Xgwm44、Xwmc702、Xwmc438、Xwmc121、Xgwm111和Xbarc121与该基因连锁,最近的为Xwmc702和Xwmc438,遗传距离分别为3.5 cM和4.3 cM。分子标记及其相关分析表明,此基因可能来自黑麦,与已定位于7D染色体上的抗病基因不同,暂命名为YrM8003。利用与其紧密连锁的标记Xwmc702和Xwmc438测黄淮麦区43个主栽品种,结果显示,有20%的品种具有与YrM8003基因相同的标记位点。这一结果有助于YrM8003在抗条锈病育种的应用。     

Quantitative and molecular characterization of heat tolerance in hexaploid wheat

Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate inheritance of heat tolerance and the minimum number of genes for the trait in bread wheat by combining quantitative genetic estimates and molecular marker analyses. Two cultivars, Ventnor (heat-tolerant) and Karl92 (heat-susceptible), were crossed to produce F₁, F₂, and F₃populations, and their grain-filling duration (GFD) at 30/25 ^°C 16/8 h day/night was determined as a measure of heat tolerance. Distribution of GFD in the F₁ and F₂ populations followed the normal model (χ², p > 0.10). A minimum of 1.4 genes with both additive and dominance effects, broad-sense heritability of 80%, and realized heritability of 96%for GFD were determined from F₂ and F₃ populations. Products from 59primer pairs among 232 simple sequence repeat (SSR) pairs were polymorphic between the parents. Two markers, Xgwm11 andXgwm293, were linked to GFD by quantitative trait loci (QTL) analysis of the F₂ population. The Xgwm11-linked QTL had only additive gene action and contributed 11% to the total phenotypic variation in GFD in the F₂population, whereas the Xgwm293-linked QTL had both additive and dominance action and contributed 12% to the total variation in GFD. The results demonstrated that heat tolerance of common wheat is controlled by multiple genes and suggested that marker-assisted selection with microsatellite primers might be useful for developing improved cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

发掘人工合成小麦中千粒重QTL的有利等位基因

以人工合成小麦Am3为供体亲本,普通小麦莱州953为轮回亲本,经5次回交然后自交,培育出含85个株系的F_2:3群体。以该群体为材料,用348对多态性SSR标记,进行全基因组扫描,发掘人工合成小麦中千粒重QTL的有利等位基因。利用复合区间作图法检测到3个千粒重QTL,其对表型变异的贡献率为10.9%~33.79%。其中,Am3的等位基因能够增加千粒重2.3~4.8 g。相关分析表明,该导入系群体的千粒重与穗粒数、穗数和株高无显著相关性。千粒重QTL与穗粒数、穗数性状的QTL不在同一位置,这有利于高千粒重基因与其他产量性状基因的聚合。采用混合线性模型作图法检测到1个千粒重QTL(QGw.caas-3D),该QTL与环境互作效应小,而且与复合区间作图法在3个环境中都检测到的QTL相同,表明QGw.caas-3D是一个稳定的主效QTL。     

Conferring resistance to pre-harvest sprouting in durum wheat by a QTL identified in <Emphasis Type="Italic">Triticum spelta</Emphasis>

Pre-harvest sprouting (PHS) causes significant yield loss and degrade the end-use quality of wheat, especially in regions with prolonged wet weather during the harvesting season. Unfortunately, the gene pool of Triticum durum (tetraploid durum wheat) has narrow genetic base for PHS resistance. Therefore, finding out new genetic resources from other wheat species to develop PHS resistance in durum wheat is of importance. A major PHS resistance QTL, Qphs.sicau-3B.1, was mapped on chromosome 3BL in a recombinant inbred line population derived from ‘CSCR6’ (Triticum spelta), a PHS resistant hexaploid wheat and ‘Lang’, a PHS susceptible Australian hexaploid wheat cultivar. This QTL, Qphs.sicau-3B.1, is positioned between DArT marker wPt-3107 and wPt-6785. Two SCAR markers (Ph3B.1 and Ph3B.2) were developed to track this major QTL and were used to assay a BC₂F₈ tetraploid population derived from a cross between the durum wheat ‘Bellaroi’ (PHS susceptible) and ‘CSCR6’ (PHS resistant). Phenotypic assay and marker-assisted selection revealed five stable tetraploid lines were highly PHS resistant. This study has successfully established that PHS-resistance QTL from hexaploid wheat could be efficiently introgressed into tetraploid durum wheat. This tetraploid wheat germplasm could be useful in developing PHS resistant durum cultivars with higher yield and good end-use quality.     

燕大1817/北农6号重组自交系群体穗部性状的QTL定位

小麦穗部性状与单株产量密切相关。本研究以小麦骨干亲本燕大1817与优良品系北农6号衍生的269个重组自交系为材料,通过在北京和河北石家庄的2年田间试验数据,利用本实验室已构建的高密度SNP和SSR遗传连锁图谱进行穗长、穗粒数和穗粒重QTL定位。采用完备复合区间作图法共检测到29个穗部性状加性效应QTL,其中10个穗长QTL分布于1B、2D、3A、3B、4A、5A、5B、6A和7D染色体上,解释的表型变异率为2.96%~9.63%,QSl.cau-4A.2在所有5个环境中均能被检测到,解释的表型变异为5.89%~9.62%,另有7个QTL能在2个或2个以上环境中被检测到;8个穗粒数相关QTL分布于1A、3A、3D、4A和5B染色体上,解释的表型变异为4.06%~11.17%,为单个环境QTL。11个与穗粒重相关QTL分布于1A、1B、2A、2D、3A、4D、5A、5B和6B染色体上,解释的表型变异为2.79%~16.12%,其中QGws.cau-1B、QGws.cau-3A和QGws.cau-6B.2在2个或者2个以上环境中能被检测到。另外,鉴定出6个分布于1A、2D、3A、4A和5B染色体上的QTL富集区段。     

野生二粒小麦导入普通小麦的抗白粉病基因MlWE29分子标记定位

小麦白粉病是严重影响小麦生产的重要病害之一,培育和应用抗病品种是有效控制和减少病害的最经济有效的方法。野生二粒小麦是硬粒小麦和普通小麦的四倍体野生祖先种,是小麦抗病性遗传改良的重要基因资源。本研究利用来自以色列的野生二粒小麦WE29与普通小麦杂交,再用普通小麦连续回交和自交,育成高抗白粉病(Blumeria graminis f. sp. tritici)小麦新品系3D258(系谱为燕大1817/WE29//5*87-1, BC₄F₆)。将3D258和高感小麦白粉病的普通小麦品种薛早配制杂交组合,对其F₁、F₂代分离群体和F₃代家系进行白粉病抗性鉴定和遗传分析。结果表明3D258携带抗白粉病显性单基因,暂命名为MlWE29。利用集群分离分析法(BSA)和分子标记分析,发现6个SSR标记(Xgwm335、Xgwm213、Xgwm639、Xwmc415、Xwmc289和Xwmc75)和5个EST-STS标记(BE494426、BE442763、CD452476、BE445282和BE407068)与抗白粉病基因MlWE29连锁。利用中国春缺体-四体系、双端体系和缺失系将抗白粉病基因MlWE29标记物理定位于5BL染色体的0.59–0.79区域。这一普通小麦抗白粉病种质资源的创制及其连锁分子标记的建立为小麦抗病基因分子标记辅助选择、基因积聚和分子育种提供了新的物质基础。     

野生二粒小麦导入普通小麦的抗白粉病基因MlWE29分子标记定位

小麦白粉病是严重影响小麦生产的重要病害之一,培育和应用抗病品种是有效控制和减少病害的最经济有效的方法。野生二粒小麦是硬粒小麦和普通小麦的四倍体野生祖先种,是小麦抗病性遗传改良的重要基因资源。本研究利用来自以色列的野生二粒小麦WE29与普通小麦杂交,再用普通小麦连续回交和自交,育成高抗白粉病(Blumeria graminis f. sp. tritici)小麦新品系3D258(系谱为燕大1817/WE29//5*87-1, BC₄F₆)。将3D258和高感小麦白粉病的普通小麦品种薛早配制杂交组合,对其F₁、F₂代分离群体和F₃代家系进行白粉病抗性鉴定和遗传分析。结果表明3D258携带抗白粉病显性单基因,暂命名为MlWE29。利用集群分离分析法(BSA)和分子标记分析,发现6个SSR标记(Xgwm335、Xgwm213、Xgwm639、Xwmc415、Xwmc289和Xwmc75)和5个EST-STS标记(BE494426、BE442763、CD452476、BE445282和BE407068)与抗白粉病基因MlWE29连锁。利用中国春缺体-四体系、双端体系和缺失系将抗白粉病基因MlWE29标记物理定位于5BL染色体的0.59–0.79区域。这一普通小麦抗白粉病种质资源的创制及其连锁分子标记的建立为小麦抗病基因分子标记辅助选择、基因积聚和分子育种提供了新的物质基础。     

Identification and genetic mapping of a powdery mildew resistance gene in wild emmer (<Emphasis Type="Italic">Triticum dicoccoides</Emphasis>) accession IW72 from Israel

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating disease of wheat (Triticum aestivum) in China and worldwide, causing severe yield losses annually. Wild emmer (T. dicoccoides) accession IW72 collected from Israel is resistant to powdery mildew at the seedling and adult stages. Genetic analysis indicated that the resistance was controlled by a single dominant gene, temporarily designated MlIW72. The F₂ population and F₃ families derived from a hybrid between IW72 and susceptible durum wheat line Mo75 were used for molecular mapping of the resistance gene. MlIW72 was linked with SSR loci Xgwm344, Xcfa2040, Xcfa2240, Xcfa2257 and Xwmc525 on the long arm of chromosome 7A. In addition, two STS markers, MAG2185 (derived from RFLP marker PSR680) and MAG1759 (developed from EST CD452874), were mapped close to MlIW72. All these markers were physically located in the terminal bin 0.86–1.00 of 7AL. The chromosome location and genetic mapping results suggested that the powdery mildew resistance gene identified in wild emmer accession IW72 might be a new allele at the Pm1 locus or a new locus closely linked to Pm1.     

小麦矮秆种质SN224的鉴定及农艺性状QTL分析

SN224是从六倍体小黑麦与普通小麦杂种后代选育的矮秆小麦种质,为对其有效利用提供参考依据,本研究对其进行了细胞学和主要农艺性状的鉴定,对它矮秆性状的遗传特点进行了分析。结果表明,SN224平均株高68.6 cm,株型较紧凑,纺锤穗、有芒、白粒,千粒重42.0 g左右,中抗条锈病和白粉病,后期不早衰,综合农艺性状较好;SN224根尖细胞染色体数目为42条,花粉母细胞减数分裂MI可观察到21个二价体,为1BL?1RS易位系;SN224/辉县红杂种F₁株高介于双亲之间,F₂群体的株高分离表现连续变异。利用已知主效矮秆基因Rht-B1b、Rht-D1b和Rht8以及1RS的特异分子标记检测证明,SN224不含有3个矮秆主效基因,1RS对SN224矮秆性状的表达没有影响。利用SN224/辉县红F₂群体,构建了含有134个标记的分子标记连锁遗传图谱,总长1332.1 cM。采用加性-完备区间作图法(ICIM-ADD)进行QTL分析,检测到2个降低株高的主效QTL QPh1B和QPh4B,分别位于1B染色体Xwmc719–Xgwm18和4B染色体Xgwm368–Xmag4284标记区间,它们可分别解释株高变异的20.0%和10.2%;检测到分别控制穗长、单株穗数和每穗小穗数的7个QTL;在4B染色体KSUM062–Xmag4284标记区间同时检测到降低株高、增加穗长和单株穗数的QTL。     

Quantitative trait loci for soil-penetrating ability of roots in durum wheat

Increasing root penetration (RP) ability into hard soil is important to improve drought resistance in durum wheat. Traits related to RP ability were evaluated in 110 recombinant inbred lines (RILs) derived from a cross between 'Jennah Khetifa' and 'Cham1' using paraffin-Vaseline (PV) discs. QTL analyses were made for the number of roots penetrating the PV disc (PVRN), total number of seminal and crown roots (TRN), RP index (PVRN/TRN) and root dry weight (DW). 'Jennah Khetifa' had higher PVRN, RP index and root DW values than 'Cham1', and the RILs showed significant differences for these traits. Two closely-linked markers, Xgwm617a and Xgwm427b , on the long arm of chromosome 6A were associated with PVRN and RP index. For root DW, a QTL was linked to marker Xgwm11 on chromosome 1B. Alleles of 'Jennah Khetifa' were associated with increased PVRN, RP index and root DW. No QTL was detected for TRN in this mapping population. The absence of co-located QTLs suggested that RP ability was controlled separately from TRN and root DW. Although the population size and number of replications were small, this study helps in understanding the complexity of root growth and the potential of marker-assisted selection for selecting genotypes with high RP ability in durum wheat populations.     

QTL-based analysis of heterosis for number of grains per spike in wheat using DH and immortalized F 2 populations

To map quantitative trait loci (QTL) and heterotic loci (HL) related to grain number per spike (GNS), 168 double haploid (DH) populations derived from Huapei?3?×?Yumai?57 and an immortalized F ₂ population (IF ₂) generated by randomly permutated intermating of these DH populations were investigated. Using inclusive composite interval mapping (ICIM), a total of nine and eight significant QTLs for GNS were detected in three different environments in DH and IF ₂ populations, respectively. QTLs on chromosomes?1A, 2B, 3B, and 6A were observed between two populations. Five QTLs were detected on chromosome?1A. Of these QTLs, QGns1A-1 was a major QTL explaining 31.25?% of phenotypic variation. QGns2B-2 detected on chromosome?2B had the most significant additive effects, explaining 46.75?% of phenotypic variation with the favorable allele contributed by Yumai?57 corresponding to an increase of 5.69?kernels. Mid-parent heterosis of each cross in the IF ₂ population was used to map heterotic quantitative trait loci. A total of 17 HLs were detected. QTLs and HLs on chromosomes?2B and 6A were observed in the IF ₂ population. Three HLs, QHgns1B-2, QHgns2B, and QHgns6A-1, were detected in two environments and expressed stably. These results showed that some intervals on chromosomes?1B, 2B, and 6A play an important role in GNS heterosis in wheat, improving understanding of this phenomenon.     

Inheritance and identification of DNA markers associated with yellow berry tolerance in wheat (Triticum aestivum L.)

Yellow berry (YB) is a serious seed disorder in durum wheat, bread wheatand triticale, which arises due to deficiency in nitrogen concentration in thesoil. YB seriously affects the grain protein content (GPC) thereby affectingbread making quality in bread wheat and pasta making quality in durumwheat. In order to study the inheritance and to identify DNA markersassociated with YB tolerance, a recombinant inbred line (RIL) populationof 113 individuals was developed by making a cross between RyeSelection111 (RS111), highly resistant to YB and Chinese Spring (CS), asusceptible parent. Phenotyping of this population to YB incidenceindicated that, at least one major gene/QTL and few minor genes governthe tolerance to YB. DNA marker analysis revealed linkage of twomicrosatellite markers Xgwm174 and Xgwm190 from chromosome 5Dwith YB tolerance while one ISSR marker UBC842₆₀₀ and oneRAPD marker OPR8₁₀₀₀ from chromosome 6B were found to beassociated with YB tolerance in repulsion phase. Association of YBtolerance with that of GPC was analyzed using the markers associated withYB tolerance. It was found to be reciprocal in this population in accordancewith the previous reports.     

QTL analysis of resistance to Fusarium head blight in wheat using a 'Wangshuibai'-derived population

Fusarium head blight (FHB) is a devastating disease that reduces the yield, quality and economic value of wheat. For quantitative trait loci (QTL) analysis of resistance to FHB, F₃ plants and F_3:5 lines, derived from a ‘Wangshuibai’ (resistant)/‘Seri82’(susceptible) cross, were spray inoculated during 2001 and 2002, respectively. Artificial inoculation was carried out under field conditions. Of 420 markers, 258 amplified fragment length polymorphism and 39 simple sequence repeat (SSR) markers were mapped and yielded 44 linkage groups covering a total genetic distance of 2554 cM. QTL analysis was based on the constructed linkage map and area under the disease progress curve. The analyses revealed a QTL in the map interval Xgwm533‐Xs18/m12 on chromosome 3BS accounting for up to 17% of the phenotypic variation. In addition, a QTL was detected in the map interval Xgwm539‐Xs15/m24 on chromosome 2DL explaining up to 11% of the phenotypic variation. The QTL alleles originated from ‘Wangshuibai’ and were tagged with SSR markers. Using these SSR markers would facilitate marker‐assisted selection to improve FHB resistance in wheat.     

Upland rice breeding in Brazil: a simultaneous genotypic evaluation of stability, adaptability and grain yield

A durum wheat recombinant inbred line population developed from PDW 233 × Bhalegaon 4 cross was analyzed in five environments to understand the genetic network responsible for test weight (TW), thousand kernel weight (TKW), grain yield (YLD), spike length (SL), spikelets per spike (SPS), kernels per spike (KER) and kernel weight per spike (KWS). Genotype, environment and their interactions were main sources of variance for all the traits. TW and TKW were influenced by 11 main effect QTL and 6 digenic epistatic interactions detected on chromosomes 2A, 2B, 4B and 7A. Grain yield was influenced by three epistatic interactions and five main effect QTL, of which two on chromosome 2A were most consistent. A major QTL for spike length was observed on chromosome 3B. QTL for spike characters were distributed over 9 chromosomes. All the traits showed significant influence of digenic epistasis (QQ) and, to a certain extent, QTL × environment interactions (QQE). Therefore, while breeding for complex traits like kernel characters and grain yield components, these interactions should also be considered important. The consistent QTL on chromosome 2A between the marker interval Xgwm71.2–Xubc835.4 with pleiotropic effect on TW and TKW, may be utilized in early generation selection to improve TW and TKW and thereby the milling potential of the durum wheat.     

Genomic characterization of drought tolerance-related traits in spring wheat

Drought tolerance was investigated in ‘C306’, one of the most drought tolerant wheat cultivars bred in India in the 1960’s. An intervarietal mapping population of recombinant inbred lines of the cross ‘C306’ × ‘HUW206’ was evaluated for drought tolerance components, namely potential quantum efficiency of photosystem (PS) II (F_v/F_m), chlorophyll content (Chl), flag leaf temperature (Lt), and grain yield per plant (Gyp) under stress. Three independent experiments were conducted under well-watered and water-stressed conditions in greenhouses and growth chambers at Kansas State University (USA). Five hundred and sixty microsatellite markers covering the entire genome were screened for polymorphism between the parents. A QTL (QLt.ksu-1D) for Lt (low flag leaf temperature under stress) on the short arm of chromosome 1D between markers Xbarc271 and Xgwm337 at LOD 3.5 explained 37% of the phenotypic variation. A QTL for F_v/F_m (QF _v /F _m .ksu-3B) and Chl (QChl.ksu-3B) controlling quantum efficiency of PS II and chlorophyll content under stress were co-localized on chromosome 3B in the marker interval Xbarc68–Xbarc101 and explained 35–40% of the phenotypic variation for each trait. A QTL (QGyp.ksu-4A) for Gyp on chromosome 4A at a LOD value of 3.2 explained 16.3% of the phenotypic variation. Inconsistent QTLs were observed for F_v/F_m on chromosomes 3A, 6A, 2B, 4B, and 4D; for Chl on 3A, 6A, 2B and 4B; and for Lt on 1A, 3A 6A, 3B and 5B. The identified QTLs give a first glimpse of the genetics of drought tolerance in C306 and need to be validated in field experiments using the marker-phenotype linkages reported here.     

Selection response for carbon isotope discrimination in a Triticum polonicum×T. durum cross: Potential interest for improvement of water efficiency in durum wheat

This study has been conducted to evaluate the usefulness of carbon isotope discrimination (δ) in mature kernels as a criterion for the improvement of water-use efficiency and yield under drought in durum wheat. For this purpose, Triticum durum‘Om Rabi 5’ was crossed with T. polonicum pseudochrysospermum 9 (Tp9) which has been found to be more drought tolerant and to have a lower carbon isotope discrimination value of the grain. The F₂ population showed a wide segregation for carbon isotope discrimination. Further, divergent selections (selection of plants most different in carbon isotope discrimination) were made among individual F₂ plants, and for carbon isotope discrimination in F₃ progenies under field conditions. Selected F₃ and F₄ progenies were evaluated under field conditions for morphological and agronomical traits. Broad-sense heritability (h²_b), response to selection and realized heritability (h²_r) were high. The narrow-sense heritability (h²_n= 0.37 ± 0.047) indicated that additive and dominance effects were involved in the genetic control of carbon isotope discrimination. Negative correlations were noted between carbon isotope discrimination and grain yield and between carbon isotope discrimination and biomass yield within years and generations. An explanation of this result is attempted by analysing the relationships between carbon isotope discrimination and several phenological and morphological traits influencing the water-use efficiency. The divergent groups selected for low and high carbon isotope discrimination exhibited significant differences for days to heading, plant height, shape of the spike and number of spikelets per spike. Correlations were also found between carbon isotope discrimination and plant height, harvest index, shape of the spike, spike length, and number of spikes per plant. The potential use of carbon isotope discrimination as a criterion for the improvement of water-use efficiency in durum wheat is discussed by considering the genetics of this trait (variability, heritability, response to selection) and also the associations with phenological and morphological traits.