Breeding for end-use quality: Reflections on the Nebraska experience

Every cultivar released in Nebraska must have four characteristics:improved agronomic performance relative to existing cultivars, exceptionalwinterhardiness, resistance to Puccinia graminis (the causal agent ofstem rust), and acceptable end-use quality. This paper will discuss ourstrategy for breeding cultivars with acceptable end-use quality. Allexperimental lines are derived from crosses with at least one or moreparents with acceptable end-use quality. As soon as individual lines areidentified (F₅) generation, microquality analyses are conducted andapproximately 10% are discarded on the basis of poor end-use quality. Inthe F₆ and later generations, samples are composited from three ormore locations/year, milled on a Buhler Mill, and baked using 100 g offlour per loaf. Though genotype-by-environmental interactions are large forend-use quality traits, composite samples are satisfactory for determiningthe end-use quality when repeated over time. By using phenotypicselection, the program has released cultivars with acceptable qualityinvolving known `poor' quality genes and chromosomes, such ashigh-molecular weight (HMW) glutenin subunits 2+12 (Scout 66 andLancota), 1BL.1RS (heterogeneous in Rawhide and homogeneous inCougar), and 1AL.1RS (heterogeneous in Nekota and Niobrara).Phenotypic selection is preferred to genotypic selection.     

Marker assisted selection to improve HMW-glutenins in wheat

The present work presents the application of new markers based on thePCR technology to amplify the complete coding sequence of the specificalleles of the high molecular weight (HMW) glutenin genes. A set ofAS-PCR molecular markers of the Glu-A1 and Glu-D1 genes wasdesigned, making use of the minor differences between the sequences of thex1, xNull and x2 of Glu-A1, x2, x5, y10 and y12 of Glu-D1. These markers were applied to assist selection inbackcross progenies to improve the glutenin quality in Spanish wheat. Theselection was also assisted using other polymorphic systems (AFLPs) inrecovering the genetic background of the recurrent parent.     

Gli-B3/Glu-B2 encoded prolamins do not affect selected quality properties in the durum wheat cross 'Abadía'×'Mexicali 75'

A study was made of the effects of the Gli-B3/Glu-B2 encoded prolamins on durum-wheat quality. Twenty-six F₃ lines from the durum wheat cross ‘Abadia’בMexicali 75’ were analysed electrophoretically for prolamin composition and for the following quality parameters: SDS sedimentation value, mixing properties, and percentage grain protein and percentage vitreous kernels. The results showed that the presence or absence of the Gli-B3/Glu-B2 encoded prolamins did not result in any significant difference in the quality characteristics of the F₃ lines; however, as expected, the LMW glutenins encoded at Glu-B3 showed large differences and are therefore the major prolamins influencing durum wheat gluten quality.     

Relationship between common wheat (Triticum aestivum L.) gluten proteins and dough rheological properties

This paper reports the correlation between the rheological properties of bread wheat dough and the types and quantities of endosperm proteins in 28 common wheat cultivars. Different methods were used to analyse the allelic composition of these cultivars and the relative quantities of the different proteins contributing to the gluten structure. Neither dough strength (W) nor tenacity/extensibility (P/L) correlated with allelic composition. Different wheats with the same allelic composition (i.e., with respect to glutenins) showed different rheological properties. The glutenins were the most influential components of W and P/L, especially the high molecular weight (HMW) glutenin subunits and in particular the type x form. These proteins seem to increase W and are the main constituents of the gluten network. The gliadins and low molecular weight (LMW) glutenin subunits appear to act as a “solvent”, and thus modify the rheological properties of the dough by either interfering with the polymerisation of the HMW glutenin subunits, or by altering the relative amounts of the different types of glutenin available. Thus, the protein subunits coded for by the alleles Glu-B1x7 and Glu-D1x5 stabilised the gluten network, whereas those coded for by Glu-B1x17 and Glu-D1x2 had the opposite effect. Dough properties therefore appear to depend on the glutenin/gliadins balance, and on the ratio of the type x and type y HMW proteins. The influence of external factors seems to depend on the allelic composition of each cultivar.     

Introduction of high molecular weight glutenin subunits 5 + 10 for the improvement of the bread-making quality of hexaploid triticale

In an earlier study, chromosome 1D of the hexaploid breadwheat cultivar ‘Chinese Spring’ was introduced into hexaploid triticale to improve its bread‐making quality. That specific chromosome, 1D, carried the a allele at the Glu‐D1 locus coding for high molecular weight (HMW) glutenin subunits 2 + 12, and since subunits 2 + 12 are associated with poor bread‐making quality in wheat, in the present study hexaploid 1D substitution triticale was crossed with octoploid triticale with the d allele at the Glu‐D1 locus encoding HMW glutenin subunits 5 + 10. Following backcrosses to different triticale varieties, 1D substitution lines were established that had Glu‐D1 allele a or d in an otherwise genetically similar background, and the influence of these two different alleles on bread‐making quality of hexaploid triticale was compared. The agronomic performance of 76 selected lines was evaluated in a field trial. The Zeleny sedimentation value was determined as a parameter for bread‐making quality, and related to the presence of chromosome 1D, the different glutenin alleles and the nature of the substitution. The presence of chromosome 1D had a significant and positive effect on the Zeleny sedimentation value, but the difference between the two glutenin alleles 2 + 12 and 5 + 10 was not as obvious as in wheat. Owing to its high cytological stability and minimal effect on agronomic performance, substitution 1D(1A) appears to be the most desirable one to use in triticale breeding.     

Segregation for isozymes and HMW glutenins in a doubled-haploid cross of winter wheat carrying 1BL.1RS and 5DL.5RS translocations from rye

The doubled haploid (DH) wheat line ‘dh 5841’ carrying two translocations from rye, 5DL.5RS and 1BL.1RS, has been crossed to the subline of wheat cultivar ‘Amadeus 7143’ with a 1BL.1RS translocation. The resulting F₁ hybrid IJ 98 with a heterozygous 5DL.5DS‐5DL.5RS chromosome pair has been used to produce doubled haploids. A total of 57 DH lines were obtained from plantlets regenerated in anther culture after successful colchicine treatment and seed set. These lines were identified regarding the constitution of chromosome 5D (5DL.5DS or 5DL.5RS) by means of isoenzyme marker analysis. Thirty DH lines possessed the 5DL.5DS chromosome, while the remaining 27 lines carried the 5DL.5RS translocation. For some of these lines, the 5DL.5RS chromosome was cytologically confirmed by C‐banding. Furthermore, the DH lines were evaluated for their high molecular weight glutenin subunit composition. All possible combinations for the four independent loci —Skdh, Glu‐Al, Glu‐B1 and Glu‐D1— were detected in only 57 DH lines and no segregation distortion was observed.     

北方麦区小麦品种高分子量谷蛋白亚基组成及其与品质性状的关系

为了解北方麦区小麦品种的遗传多样性,挖掘可供利用的优异高分子量谷蛋白亚基(HMW-GS)类型,为品质改良提供基础材料,利用聚丙烯酰胺凝胶电泳方法(SDS-PAGE),分析了172份北方麦区部分小麦品种的HMW-GS组成,并对其与蛋白质含量和沉降值之间的关系进行了研究。结果表明:Glu-A1、Glu-B1和Glu-D1分别具有3种、6种和3种不同的亚基类型。亚基1、7+9和5+10在各自位点上出现的频率最高,分别达到了54.07%、48.26%和49.42%。3个位点亚基对蛋白质含量的效应可分别表示为:1≥2*Null,13+16≥14+15≥17+18≥7+87+96+8,5+102+124+12;对沉降值的作用可分别表示为:2*≥1Null,14+15≥17+187+8≥13+167+96+8,5+102+124+12。亚基组成类型共有24种,在蛋白质含量水平上,亚基组成1/14+15/5+10、1/14+15/2+12、1/7+8/5+10、1/17+18/5+10和1/7+9/5+10相对较高;在沉降值水平上,亚基组成1/14+15/5+10、1/17+18/5+10、1/7+8/5+10、2*/7+9/5+10和1/14+15/2+12相对较高。综上所述,在24种亚基组成类型中没有发现明显优势的组合类型,优质亚基2*、17+18和14+15出现的频率较低。江苏省中筋和弱筋小麦品种选育,应结合蛋白质含量、沉降值和亚基组成进行改良。     

山西省不同来源小麦品种(系)的HMW-GS组成分析

为了解山西小麦品质现状并且为今后山西小麦育种提供材料和依据,利用十二烷基硫酸钠聚丙烯酰胺凝胶电泳(Sodium dodecyl sulfate polyacrylamide gel electrophoresis,SDS-PAGE)方法分析123份山西小麦品种资源高分子量谷蛋白亚基(High molecular weight glutenin subunits,HMW-GS)的组成。结果表明:在123份供试材料中,共检测出18种HMW-GS,其中Glu-A1位点上有1、2*和Null共3种,Glu-B1位点上有7+8、7+9、7、6+8、17+18、14+15、20、13+16和13+19共9种,Glu-D1位点上有2+12、5+10、5+12、2+10、3+12和4+12共6种;亚基Null、7+8和2+12在各自位点上出现频率最高,分别为78.05%、60.16%和65.85%。亚基组合类型共34种,主要是Null/7+8/2+12,占45.53%,其次是Null/7+9/2+12,占12.20%,优良亚基组合类型1/7+8/5+10与1/17+18/5+10相当缺乏。育成品种与地方品种比较分析发现,在Glu-A1位点上优良亚基1提高14.16%;Glu-B1位点上7+8下降9.05%;Glu-D1位点上5+10在地方品种中没有出现,但在育成品种中达14.89%。同时筛选出10份得9和10分的优质品种资源,还有12份含稀有亚基的品种资源,可作为山西今后小麦品质育种的亲本材料。     

施氮时期对小麦籽粒HMW-GS积累及GMP粒度分布的影响

在225 kg hm^-2施氮水平下, 设置起身肥(SE, GS 30), 拔节肥(JT, GS 32)和孕穗肥(BT, GS 41) 3个追施氮肥处理(底追比1:1), 研究了追肥时期对强筋小麦济南17和弱筋小麦鲁麦21籽粒HMW-GS积累和GMP粒度分布的影响。结果表明, 两品种籽粒HMW-GS于花后14 d均已形成, 济南17籽粒HMW-GS和GMP含量均高于鲁麦21, 说明强筋小麦具有较强的谷蛋白积累能力。济南17成熟期籽粒HMW-GS和GMP含量以SE处理最高, 施氮时期后移其含量呈下降趋势。JT处理显著提高鲁麦21灌浆中后期HMW-GS的积累速度, 延长HMW-GS的快速积累期。济南17 SE处理和鲁麦21 JT处理的籽粒x型亚基(1、4或5、7)在灌浆中后期的积累速率显著提高。追肥时期对y型亚基的积累速率无显著影响。追氮时期后移均提高两品种籽粒GMP小颗粒的(粒径<12 μm)体积和表面积百分比, 降低大颗粒(粒径>100 μm)体积和表面积百分比。济南17粒径>12 μm的GMP颗粒数目百分比因追氮时期后移而增加, 鲁麦21粒径>12 μm的GMP颗粒数目百分比则降低。含4+12亚基的强筋小麦济南17比含5+10亚基的弱筋小麦鲁麦21偏向于更高的大颗粒体积比例, 说明亚基间的聚合和GMP颗粒的分布不仅与亚基类型有关, 而且与单位面粉中亚基的含量密切相关。     

Assessment of genetic variability in hexaploid wheat landraces of Pakistan based on polymorphism for HMW glutenin subunits

Summary Sixty hexaploid wheat landraces collected from five regions of Pakistan were assessed for genetic variability in terms of high molecular weight (HMW) glutenin subunits as revealed by SDS-PAGE. The germplasm appeared to be diverse and unique on the basis of HMW glutenin subunit compositions. Out of 24 alleles detected at all the Glu-1 loci, four belonged to Glu-A1, 12 to Glu-B1 and eight to Glu-D1 locus. The number of novel HMW glutenin subunits detected were 1, 4 and 6 at the three loci (Glu-A1, Glu-B1, Glu-D1), respectively. The frequency distribution patterns of 24 allelic variants detected at the three Glu-1 loci in 1080 samples analysed for 60 accessions were determined both on the basis of individual accessions and on the basis of regions (accessions pooled across the regions). One allele (null) at the Glu-A1 locus, three alleles (17+18, 7+8, 14) at the Glu-B1 locus and, two alleles (2+12 and 2^**+12) at the Glu-D1 locus were found most frequently distributed in the 60 populations. Maximum variation was observed in the Baluchistan and Gilgit regions of Pakistan in terms of distribution of novel Glu-1 alleles. A higher gene diversity was observed between the populations as compared to the gene diversity within the populations while, a reverse pattern of gene diversity was observed when populations were pooled across the regions (higher within the regions than between the regions). A data base has been generated in this study which could be expanded and usefully exploited for cultivar development or management of gene bank accessions.