Reduced height (Rht) and photoperiod insensitivity (Ppd) allele associations with establishment and early growth of wheat in contrasting production systems

Near isogenic lines (NILs) varying for genes for reduced height (Rht) and photoperiod insensitivity (Ppd-D1a) in a cv. Mercia background (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht8c + Ppd-D1a, Rht-D1c, Rht12) were compared at one field site but within contrasting (‘organic’ vs. ‘conventional’) rotational and agronomic contexts, in each of 3 years. In the final year, further NILs (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht-B1b + Rht-D1b, Rht-D1b + Rht-B1c) in both Maris Huntsman and Maris Widgeon backgrounds were added together with 64 lines of a doubled haploid (DH) population [Savannah (Rht-D1b) × Renesansa (Rht-8c + Ppd-D1a)]. Assessments included laboratory tests of germination and coleoptile length, and various field measurements of crop growth between emergence and pre jointing [plant population, tillering, leaf length, ground cover (GC), interception of photosynthetically active radiation (PAR), crop dry matter (DM) and nitrogen accumulation (N), far red: red reflectance ratio (FR:R), crop height, and weed dry matter]. All of the dwarfing alleles except Rht12 in the Mercia background and Rht8c in the DHs were associated with reduced coleoptile length. Most of the dwarfing alleles (depending on background) reduced seed viability. Severe dwarfing alleles (Rht-B1c, Rht-D1c and Rht12) were routinely associated with fewer plant numbers and reduced early crop growth (GC, PAR, DM, N, FR:R), and in 1 year, increased weed DM. In the Mercia background and the DHs the semi-dwarfing allele Rht-D1b was also sometimes associated with reductions in early crop growth; no such negative effects were associated with the marker for Rht8c. When significant interactions between cropping system and genotype did occur it was because differences between lines were more exaggerated in the organic system than in the conventional system. Ppd-D1a was associated positively with plant numbers surviving the winter and early crop growth (GC, FR:R, DM, N, PAR, height), and was the most significant locus in a QTL analysis. We conclude that, within these environmental and system contexts, genes moderating development are likely to be more important in influencing early resource capture than using Rht8c as an alternative semi-dwarfing gene to Rht-D1b.     

A 192bp allele at the <Emphasis Type="Italic">Xgwm261</Emphasis> locus is not always associated with the <Emphasis Type="Italic">Rht8</Emphasis> dwarfing gene in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The height-reducing gene Rht8 was introduced into Italian wheats by breeder Nazareno Strampelli from the Japanese landrace Akakomugi, and has been widely used in wheats adapted to southern and eastern European conditions. Following identification of a close linkage to Rht8, microsatellite marker Gwm261 has been used extensively to screen large numbers of diverse international germplasm. A 192bp allele at this locus has been taken as “diagnostic” for Rht8 and used to infer the international distribution of Rht8. In this paper, we report several instances of cultivars and mapping populations that vary for the presence of the 192bp allele at the Xgwm261 locus (Xgwm261 ₁₉₂ ), but with no associated reduction in height, suggesting a lack of association with Rht8. For instance, in the population derived from a cross between Sunco (Rht-B1b, Xgwm261 ₁₆₅ ) and Tasman (Rht-D1b, Xgwm261 ₁₉₂ ), there were significant height differences associated with the segregation of Rht-B1b and Rht-D1b, but no height differences between Xgwm261 genotypes. Similar results were obtained in a population derived from the cross between Molineux (Rht-B1b, Xgwm261 ₁₉₂ ) and Trident (Rht-D1b Xgwm261 ₂₀₈ ). In contrast, the cross between Trident and Chuanmai 18 (Xgwm261 ₁₉₂ ) gave significant height effects at both the Rht-D1 and Xgwm261 loci, with no epistatic interaction between loci. Chuanmai 18 is closely related to the Strampelli wheat Mara (ancestrally derived from Akakomugi) and is therefore likely to carry Rht8. The old Japanese cultivar Norin 10, used by Norman Borlaug to introduce Rht-B1b and Rht-D1b into Mexican wheats, also has a 192bp allele at the Xgwm261 locus, and the sequence of the amplified product is identical to that of Akakomugi. We suggest that the widespread use of Norin 10-derived germplasm during and after the Green Revolution introduced a second haplotype into international germplasm, in which Xgwm261 ₁₉₂ has no association with Rht8. Therefore, the presence of Xgwm261 ₁₉₂ is only indicative of Rht8 in wheat cultivars that have inherited this allele from Akakomugi or a Strampelli wheat ancestor.     

Distribution of the photoperiod insensitive <Emphasis Type="Italic">Ppd-D1a</Emphasis> allele in Chinese wheat cultivars

Photoperiod response is of great importance for optimal adaptation of bread wheat cultivars to specific environments, and variation is commonly associated with allelic differences at the Ppd-D1 locus on chromosome 2D. A total of 926 Chinese wheat landraces and improved cultivars collected from nine wheat growing zones were tested for their genotypes at the Ppd-D1 locus using allele-specific markers. The average frequency of the photoperiod-insensitive Ppd-D1a allele was 66.0%, with the frequencies of 38.6 and 90.6% in landraces and improved cultivars, respectively. However, the Ppd-D1a allele was present in all improved cultivars released after 1970 except for spring wheats in high latitude northwestern China, and winter wheats in Gansu and Xinjiang. The presence of the Ppd-D1a allele in landraces and improved cultivars increased gradually from north to south, illustrating the relationship between photoperiod response and environment. Ppd-D1a in Chinese wheats is derived from three sources, Japanese landrace Akagomughi and Chinese landraces Mazhamai and Youzimai. The current information is important for understanding the broad adaptation of improved Chinese wheat cultivars. F. P. Yang and X. K. Zhang contributed equally to this work.     

春化、光周期和矮秆基因在不同国家小麦品种中的分布及其效应

为促进国外种质资源在我国的有效利用,将14个国家的100份代表性小麦品种在国内的8个代表性地点种植,调查抽穗期、成熟期和株高,并以4个春化基因(Vrn-A1、Vrn-B1、Vrn-D1和Vrn-B3)、1个光周期基因(Ppd-D1a)及2个矮秆基因(Rht-B1b和Rht-D1b)的分子标记检测所有品种的基因型。春化基因Vrn-A1a、Vrn-B1、Vrn-D1和vrn-A1+vrn-B1+ vrn-D1的分布频率分别为8.0%、21.0%、21.0%和64.0%;显性等位变异Vrn-A1a、Vrn-B1和Vrn-D1主要存在于来自中国春麦区及意大利、印度、加拿大、墨西哥和澳大利亚的品种中,这些品种一般为春性类型;春化位点均为隐性等位变异或vrn-A1+vrn-D1+Vrn-B1的品种主要分布在中国冬麦区、美国冬麦区、俄罗斯冬麦区,以及英国、法国、德国、罗马尼亚、土耳其和匈牙利,这些地区的小麦均为冬性类型。秋播时,供试品种均能正常抽穗,且携带春化显性变异的材料较隐性类型抽穗早,显性等位变异表现加性效应,4个春化位点均为隐性变异的一些欧美材料因抽穗太晚在杨凌和成都不能正常成熟;而春播时,显性等位变异基因型抽穗的频率高,隐性等位变异基因型基本不能抽穗。光周期不敏感基因Ppd-D1a的分布频率为68.0%,主要分布在中国、法国、罗马尼亚、俄罗斯、墨西哥、澳大利亚和印度,而光周期敏感等位变异Ppd-D1b主要分布在英国、德国、匈牙利和加拿大等中高纬度地区;携带Ppd-D1a的品种较携带Ppd-D1b的品种抽穗早,大多数Ppd-D1a品种在长日照和短日照条件下均能成熟,大部分Ppd-D1b品种在短日照条件下不能成熟。Rht-B1b和Rht-D1b基因的分布频率分别为43.0%和35.0%,其中Rht-B1b主要分布于美国、罗马尼亚、土耳其、意大利、墨西哥和澳大利亚,Rht-D1b主要分布于中国、德国、英国、意大利和印度。一般来说,一个国家的品种携带Rht-B1b或Rht-D1b之一,而这2个基因在高纬度地区分布频率较低。Rht-B1b、Rht-D1b和Ppd-D1a的降秆作用均达显著水平,Rht-B1b和Rht-D1b的加性效应突出。     

Identification,distribution and effects on agronomic traits of the semi-dwarfing <Emphasis Type="Italic">Rht</Emphasis> alleles in Bulgarian common wheat cultivars

Bulgarian common wheat cultivars released in the period 1925–2003 were studied using the gibberellic acid (GA) test and microsatellite analysis of the Xgwm261 locus on chromosome 2DS to identify the semi-dwarfing (Rht) genes. The old cultivars, isolated through selection from landraces, carried rare alleles (211- and 215-bp) at Xgwm261 locus, and those developed by hybridisation to foreign cultivars, carried the 165- and 174-bp alleles. Forty-two (55.3%) of 76 modern cultivars were GA-responsive. The 192-bp allele, diagnostic for Rht8, was observed in 64 (84.2%) modern cultivars, of which 37 carry Rht8 alone, and 27 possess a combination of Rht8 and a GA-insensitive allele viz. Rht-B1d (17); Rht-D1b (6) and Rht-B1b (4). The 174-bp allele is present in seven cultivars, only one of which is photoperiod-sensitive, and the rest are day-length insensitive. The 203-bp allele was found in six modern cultivars. Cultivars carrying the Rht8 allele are the most widespread and some of them have been cultivated for a long period. Cultivars with the `Saitama 27' allele (Rht-B1d) are the most productive and are second in distribution in the country. The recently observed trend for increasing the proportion of cultivars with GA-insensitive Rht genes is probably due to their combination with the 192-bp allele of Xgwm261 locus tightly linked to the Ppd-D1, to the break of the link between the 174-bp allele and ppd-D1, and to the introduction of other genes influencing flowering time.     

Confirmation of the relationship between plant height and Fusarium head blight resistance in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) by QTL meta-analysis

Fusarium head blight (FHB) is a serious wheat disease all over the world. In this study, the relationships between plant height (PH) and FHB were investigated across the whole wheat genome by QTL meta-analysis from fifty-six experiments. Coincident meta-QTL (MQTL) for PH and FHB were found on chromosomes 2D, 3A, 4B, 4D and 7A. Rht-B1, Rht-D1, Rht8, MQTLs P7 and P26 were consistent with FHB MQTLs. The meta-analysis results confirmed the negative associations of Rht-B1, Rht-D1, and Rht8 with FHB resistance. The associations of PH and FHB resistance on chromosomes 3A and 7A have not been reported and need further investigation. These regions should be given attention in breeding programs. MQTLs derived from several resistance sources were also observed. Some FHB MQTLs for different types of resistance overlapped. These findings could be useful for improving wheat varieties with resistance to FHB.     

Phosphorus use efficiency in tall, semi-dwarf and dwarf near-isogenic lines of spring wheat

The impact of the Rht dwarfing genes on P utilization efficiency (PUTE = grain dry matter per kg P in above-ground biomass), total P uptake (Pt) and related traits was studied in the varietal backgrounds of two tall wheat cultivars, Maringa and Nainari 60. Four sets of near-isogenic lines carrying different combinations of the alleles Rht-B1b, Rht-D1b and Rht-B1c for gibberellin-insensitive dwarfism in the hexaploid wheat (Triticum aestivum L.) were compared with tall controls in two field trials under conditions of adequate nutrient supply and irrigation in Northwest Mexico. The yield-increasing effect of the dwarfing genes Rht-D1b and Rht-B1b led to improved PUTE in Maringa and total P uptake in both cultivars. Also, the double dwarf line of Maringa had larger grain yields and P uptake compared to the tall control. The Rht-B1c genotypes showed low PUTE, thick roots and high P concentration in vegetative biomass indicating a surplus of assimilates and P, which could not be translocated into the grains. A similar problem could be observed in Nainari 60 with Rht-B1b and Rht-D1b, which produced the largest grain dry matter with the lowest P concentrations in grains although they showed high P accumulation in straw. Most of the net P uptake occurred before anthesis. P absorption after anthesis was more critical for the dwarf genotypes. For double dwarfs and Rht-B1c, respectively, only 3% and 21% of the total accumulated P at maturity was absorbed at post-anthesis. The grain P of the dwarf lines came more from P accumulated at pre-anthesis and translocated from the vegetative biomass into the grain. The pre-anthesis P accumulation was positively correlated with spikes per m² (r = 0.91), whereas post-anthesis P accumulation correlated better with grains per spike(r = 0.72), and thousand kernel weight (r = 0.51). P uptake efficiency played a secondary role under these non-P-limiting conditions, and differences in root length density were only slightly affected by Rht-genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polymorphism of waxy proteins in Iberian hexaploid wheats

A collection of 130 cultivars of bread wheat, 332 landraces of bread wheat and 144 spelt wheats was analysed for waxy proteins in the grain. The electrophoretic patterns showed very low polymorphism and most of the hexaploid wheats had the Wx-Ala, Wx-D1a and Wx-B1 alleles of ‘Chinese Spring’. Two alleles were detected at Wx-A1 (Wx-A1a, and Wx-A1b (null)), the latter was present in only 5.1% of the bread wheat landraces and 7.6% ofthe spelt wheats. No allelic variation was found at the Wx-D1 locus and all the hexaploid wheats had the Wx-D1a allele. Wx-B1 was the most polymorphic locus, with three alleles detected: Wx-B1a, Wx-B1b (null) and Wx-Blc coding for a Wx-B1 protein with a slightly different mobility from Wx-B1a. The null Wx-B1b allele was found in 10.8% of the bread wheat cultivars, 21.4% of the bread wheat landraces and 12.5% of the spelt wheats. Among the 604 hexaploid wheats analysed, only two bread wheat landraces (0.6%) and two spelt wheats (1.4%) had the null allele at both Wx-A1 and Wx-B1 loci.     

Genotype analysis of the wheat semidwarf Rht‐B1b and Rht‐D1b ancestral lineage

In wheat, semidwarfism resulting from reduced height (Rht)‐B1b and Rht‐D1b was integral to the ‘green revolution’. The principal donors of these alleles are ‘Norin 10’, ‘Seu Seun 27’ and ‘Suwon 92’ that, according to historical records, inherited semidwarfism from the Japanese landrace ‘Daruma’. The objective of this study was to examine the origins of Rht‐B1b and Rht‐D1b by growing multiple seed bank sources of cultivars comprising the historical pedigrees of the principal donor lines and scoring Rht‐1 genotype and plant height. This revealed that ‘Norin 10’ and ‘Suwon 92’ sources contained Rht‐B1b and Rht‐D1b, but the ‘Seu Seun 27’ source did not contain a semidwarf allele. Neither Rht‐B1b nor Rht‐D1b could be definitively traced back to ‘Daruma’, and both ‘Daruma’ sources contained only Rht‐B1b. However, ‘Daruma’ remains the most likely donor of Rht‐B1b and Rht‐D1b. We suggest that the disparity between historical pedigrees and Rht‐1 genotypes occurs because the genetic make‐up of seed bank sources differs from that of the cultivars actually used in the pedigrees. Some evidence also suggests that an alternative Rht‐D1b donor may exist.     

High molecular weight glutenin subunit composition of Chinese bread wheats

Summary The endosperm storage proteins of 205 Chinese bread wheat cultivars and advanced lines were fractionated by SDS-PAGE to determine their high molecular weight (HMW) glutenin subunit composition. Seventeen alleles were identified: three at Glu-A1, eight at Glu-B1, and six at Glu-D1. The most common alleles were Null, 1, 7+8, 7+9, and 2+12. The results indicate that wheats from different regions differ in their frequencies of HMW glutenin subunits, however, none of the subunits could be related to specific environments. The glutenin quality scores of Chinese wheats ranged from 3 to 10, with an average of 6.7. Increasing quality scores have implications in improving steam-bread making quality for Chinese consumers. On the basis of HMW glutenin subunit composition, Chinese wheats are close to European wheats, especially Italian wheats because several Italian introductions are widely distributed in the pedigrees of Chinese wheat.     

Effects of reduced height (<Emphasis Type="Italic">Rht</Emphasis>) and photoperiod insensitivity (<Emphasis Type="Italic">Ppd</Emphasis>) alleles on yield of wheat in contrasting production systems

Near isogenic lines (NILs) varying for reduced height (Rht) and photoperiod insensitivity (Ppd-D1) alleles in a cv. Mercia background (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht8c+Ppd-D1a, Rht-D1c, Rht12) were compared for interception of photosynthetically active radiation (PAR), radiation use efficiency (RUE), above-ground biomass (AGB), harvest index (HI), height, weed prevalence, lodging and grain yield, at one field site but within contrasting (‘organic’ vs. ‘conventional’) rotational and agronomic contexts, in each of 3 years. In the final year, further NILs (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht-B1b+Rht-D1b, Rht-D1b+Rht-B1c) in Maris Huntsman and Maris Widgeon backgrounds were added together with 64 lines of a doubled haploid (DH) population [Savannah (Rht-D1b) × Renesansa (Rht-8c+Ppd-D1a)]. There were highly significant genotype × system interactions for grain yield, mostly because differences were greater in the conventional system than in the organic system. Quadratic fits of NIL grain yield against height were appropriate for both systems when all NILs and years were included. Extreme dwarfing was associated with reduced PAR, RUE, AGB, HI, and increased weed prevalence. Intermediate dwarfing was often associated with improved HI in the conventional system, but not in the organic system. Heights in excess of the optimum for yield were associated particularly with reduced HI and, in the conventional system, lodging. There was no statistical evidence that optimum height for grain yield varied with system although fits peaked at 85 and 96 cm in the conventional and organic systems, respectively. Amongst the DH lines, the marker for Ppd-D1a was associated with earlier flowering, and just in the conventional system also with reduced PAR, AGB and grain yield. The marker for Rht-D1b was associated with reduced height, and again just in the conventional system, with increased HI and grain yield. The marker for Rht8c reduced height, and in the conventional system only, increased HI. When using the System × DH line means as observations grain yield was associated with height and early vegetative growth in the organic system, but not in the conventional system. In the conventional system, PAR interception after anthesis correlated with yield. Savannah was the highest yielding line in the conventional system, producing significantly more grain than several lines that out yielded it in the organic system.     

Classification of GA response,Rht genes and culm length in Japanese varieties and landraces of wheat

Summary The GA response, Rht genes and culm length of 133 Norin varieties, 6 breeding lines and 16 landraces of Japanese wheat were investigated. Out of 133 Norin varieties tested, 103 were GA-insensitive and 30 GA-responsive. The 6 breeding lines were all GA-insensitive. Out of 16 landraces tested, 10 were GA-insensitive and 6 GA-responsive. Among the 10 GA-insensitive landraces, only Daruma had a Rht1 genotype. The other 9 had a Rht2 genotype. None of the landraces tested carried both Rht1 and Rht2 or Rht3. Out of the 103 GA-insensitive Norin varieties, 22 carried only Rht1, another 79 carried only Rht2, and only Norin 10 and Kokeshikomugi carried both Rht1 and Rht2. No tested variety carried Rht3. Some Norin varieties carrying Rht2 showed tall culms comparable to that of the rht tester line Chinese Spring. These results suggest that these varieties had a nullifier or modifier gene(s) or height promoting genes in the background controlling the height-reducing effect of Rht2. Conversely, six GA-responsive Norin varieties were as short as Akakomugi which carries the GA-responsive Rht genes, Rht8 and Rht9. The also seemed to carry a GA-responsive Rht gene or genes, and moreover all but one may carry gene(s) other than the Akakomugi genes. The origin of Rht1 and Rht2 of Norin 10 was speculated on the GA-response and Rht genotypes of its related varieties and landraces.     

The reduced height genes do not affect the root penetration ability in wheat

Root penetration (RP) ability into compacted soil is an important breeding target for drought avoidance by durum (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) in regions with compacted soils and water deficits. However, it is said generally that yield of the current cultivars introduced the reduced height gene (Rht-B1b or Rht-D1b) are more sensitive to drought stress than that of old landraces. This study investigated the effect of the Rht genes on RP ability using the seedlings of near-isogenic lines (NILs) of Rht genes of LD222 durum wheat and April Bearded bread wheat, and 110 recombinant inbred lines (RILs) of durum wheat derived from the cross between the tall landrace (Jennah Khetifa; Rht-B1a Rht-B1a) and semi-dwarf cultivar (Cham1; Rht-B1b Rht-B1b). One seedling of each genotype was grown in a pot (6 cm diameter, 15 cm height) with a disc of 3 mm thickness made from paraffin and Vaseline mixture (PV) in 10 cm depth, as a substitute for a compacted soil layer. The RP index [number of roots penetrating through the PV disc per plant (PVRN)/total number of seminal and crown roots per plant (TRN)] was measured at eight weeks after sowing and used as the indicator of RP ability of seedling. In NILs, the shoot length decreased significantly because of the introduction of either Rht-B1b or Rht-D1b dwarfing genes, but the RP index was similar to those of tall parents. In RILs, although the RP index and shoot length were higher in Jennah Khetifa than in Cham1, the relationship between RP index and shoot length was not significant (r = 0.156). Both results indicate that RP ability of wheat does not link to dwarfness regulated by Rht genes. We suppose therefore that it would be possible to develop a high yielding semi-dwarf cultivar with excellent RP ability.     

Breeding for salinity resistance in mulberry (<Emphasis Type="Italic">Morus</Emphasis> spp.)

Late maturity α-amylase (LMA) is a genetic defect that is fairly widely spread in bread wheat (Triticum aestivum L.) germplasm, and recently detected in durum cultivars, which can result in unacceptably high α-amylase activity (low falling number) in ripe grain. LMA has also been observed at unexpectedly high frequency and severity in synthetic hexaploid wheats derived from the interspecific hybridisation of Triticum durum (AABB) and Aegilops tauschii (DD). Since synthetic hexaploids represent an important new source of resistances/tolerances to a range of biotic and abiotic stresses for wheat breeders, there is a pressing need to understand the mechanisms involved in LMA in synthetics and develop strategies for avoiding its adverse effects on grain quality. The objectives of this study were to firstly, compare the LMA phenotype of synthetics that varied for plant height, secondly, to characterise the LMA phenotype in groups of synthetics derived from the same durum parents and finally to determine whether LMA in primary synthetics is associated with the QTL previously reported in conventional bread wheat. More than 250 synthetic hexaploids, a range of durum cultivars and a doubled haploid population derived from Worrakatta (non-LMA) × AUS29663 (high LMA synthetic) were phenotyped and genotyped with markers reported to be linked to LMA in conventional bread wheat and markers diagnostic for the semi-dwarfing gene, Rht1. More than 85% of synthetics were prone to LMA, approximately 60% ranked as very high. Genetic control of LMA in synthetic hexaploids appeared to involve QTL located on 7B, and to a lesser extent 3B, similar to bread wheats. However, the LMA phenotype of many synthetic hexaploids appeared to be more extreme than could be explained by comparisons with bread wheat even taking into account the apparent absence of Rht1 in most genotypes. Other mechanisms, possibly triggered by the interaction between the AABB and DD genomes cannot be excluded. The presence of wild type rht1 in most synthetic hexaploids and their extreme height is difficult to reconcile with the semi-dwarf, Rht1, stature of many of the durums used in the interspecific hybridisation process. Mechanisms that could explain this observation remain unclear.     

Genetic improvement of grain yield and associated traits in the southern China winter wheat region: 1949 to 2000

To understand the genetic gains of grain yield in the Southern China Winter Wheat Region (SCWWR), two yield potential trials, i.e., YPT 1 including 11 leading cultivars from the Middle and Low Yangtze Valley (Zone III) and YPT 2 including 15 leading cultivars from the Southwestern China Region (Zone IV) from 1949 to 2000, were conduced during the 2001–2003 cropping seasons. A completely randomized block design of three replicates was employed with controlled field environments. Molecular markers were used to detect the presence of dwarfing genes and the 1B/1R translocation. Results showed that average annual genetic gain was 0.31% (P < 0.05) or 13.96 kg/ha/year and 0.74% (P < 0.01) or 40.80 kg/ha/year in Zones III and IV, respectively. In YPT 1, changes of all other traits were not significant, but plant height was significantly reduced. In YPT 2, the genetic improvement of grain yield was primarily attributed to the increased thousand kernel weight (TKW) (0.65%, P < 0.01) and kernel weight/spike (0.87%, P < 0.01), reduced plant height and increased harvest index (HI). The dwarfing gene Rht 8 was most frequently present (46.1%), Rht-B1b was observed in three genotypes in Zone III, and Rht-D1b was present in only one genotype in Zone IV. The 1B/1R translocation was present in four genotypes. Utilization of Italian germplasm and development of landmark cultivar Fan 7 were the key factors for grain yield improvement in SCWWR. The future challenge of wheat breeding in this region is to continue improving grain yield and disease resistance, and to develop cultivars suitable for the reduced tillage of wheat/rice double cropping. Utilization of Mexican germplasm could provide opportunities for future yield improvement.     

Distribution of microsatellite alleles linked to Rht8 dwarfing gene in wheat

A wheat microsatellite locus, Xgwm 261, whose 192-bp allele closelylinked to the dwarfing gene Rht8, on chromosome 2D, was used toscreen 71 wheat cultivars from 13 countries to assess the variation at thislocus. Screening of this wheat collection showed that a 165-bp allele anda 174-bp allele were the most frequent. None of the New Zealand cultivarspossessed a 192-bp allele specific to Rht8, while only one cultivarfrom the US produced this important allele. The frequency of a 192-bpallele among these wheat cultivars was 5.63%. The highest allelefrequency was observed for a 174-bp fragment (52.11%) followed by a165-bp fragment (26.76%). The only durum wheat `Cham 1', did notshow any amplification due to the absence of D genome. Four new novelalleles, 180-bp, 198-bp, 200-bp and 204-bp present in the US and NewZealand wheat cultivars are reported.     

Molecular characterization of <Emphasis Type="Italic">Pina</Emphasis> and <Emphasis Type="Italic">Pinb</Emphasis> allelic variations in Xinjiang landraces and commercial wheat cultivars

Grain hardness plays an important role in determining both milling performance and quality of the end-use products produced from common or bread wheat. The objective of this study was to characterize allelic variations at the Pina and Pinb loci in Xinjiang wheat germplasm for further understanding the mechanisms involved in endosperm texture formation, and the status of grain texture in Chinese bread wheat. A total of 291 wheat cultivars, including 56 landraces, and 95 introduced and 140 locally improved cultivars, grown in Xinjiang, were used for SKCS measurement and molecular characterization. Among the harvested grain samples, 185 (63.6%), 40 (13.7%), and 66 (22.7%) were classified as hard, mixed and soft, respectively. Eight different genotypes for the Pina and Pinb loci were identified, including seven previously reported genotypes, viz., Pina-D1a/Pinb-D1a, Pina-D1a/Pinb-D1b, Pina-D1b/Pinb-D1a, Pina-D1a/Pinb-D1p, Pina-D1a/Pinb-D1q, Pina-D1a/Pinb-D1aa, Pina-D1a/Pinb-D1ab, and a novel Pinb allele, Pinb-D1ac. This new allele, detected in Kashibaipi (local landrace) and Red Star (from Russia) has a double mutation at the 257th (G to A substitution) and 382nd (C to T substitution) nucleotide positions of the coding region. Pina-D1b, Pinb-D1b, and Pinb-D1p were the most common alleles in Xinjiang wheat germplasm, with frequencies of 14.3%, 38.1% and 28.6% in hard textured landraces, 25.5%, 56.9% and 11.8% in hard introduced cultivars, and 24.8%, 47.8% and 26.5% in hard locally improved cultivars, respectively. The restriction enzymes ApaI, SapI, BstXI and SfaNI were used to identify Pinb-D1ab or Pinb-D1ac, Pinb-D1b, Pinb-D1e and Pinb-Dg, respectively, by digesting PCR products of the Pinb gene. The unique grain hardness distribution in Xinjiang bread wheat, as well as the CAPs markers for identification of the Pinb alleles provided useful information for breeding wheat cultivars with optimum grain textures. Liang Wang and Genying Li—contributed equally to this work.     

人工合成小麦与普通小麦杂交后代衍生群体的Rht8基因分析

【目的】四倍体小麦与节节麦杂交培育的人工合成小麦已广泛应用于国内外小麦品种改良。通过研究人工合成小麦与普通小麦杂交后代的Rht8基因型,有助于提高分子标记育种效率,也有助于Rht8 基因型的多态性研究,并为人工合成小麦在中国小麦品种改良和分子标记育种中的应用提供依据和方法;【方法】以引自CIMMYT的人工合成小麦分别与中国四川成都平原主栽普通小麦品种杂交、回交的BC2F2:6后代群体中选育的113份优良高代系和川麦38、川麦42、川麦43和川麦47育成品种为材料,采用特异引物的PCR 扩增和改进的聚丙烯酰胺凝胶电泳对其Rht8基因型进行了研究;【结果】在以syn768、Syn769、Syn780和Syn786人工合成小麦为亲本的117份后代衍生群体检测材料中,Rht8基因型频率为77.78%。从每一个人工合成小麦形成的小的后代衍生群体看,Rht8基因型频率各不相同。以syn768为亲本的后代衍生群体,Rht8基因型频率最高,为96.70%;在以syn769为亲本而育成的优良高代系和川麦38、川麦42与川麦43育成品种中,Rht8基因型频率最低,为71.64%;以Syn780为亲本的后代衍生群体中,Rht8基因型频率为73.68%,分离比率约为3:1;以Syn786为亲本育成的材料只有川麦47,该品种不含有Rht8该基因;【结论】不论父本或母本的Rht8的基因型状况如何,它们所产生的杂交后代材料Rht8基因的遗传是随机的。     

Genetic diversity of European spelt wheat (Triticum aestivum ssp. spelta L. em. Thell.) revealed by glutenin subunit variations at the Glu-1 and Glu-3 loci

Summary High and low molecular weight glutenin subunit (HMW-GS and LMW-GS) compositions of 270 European spelts, 15 Iranian spelts and 25 bread wheat cultivars were analyzed by one- and two-dimensional gel electrophoresis. The results revealed a total of 22 HMW-GS alleles (4 at Glu-A1, 11 at Glu-B1 and 7 at Glu-D1) and 32 allele combinations among the three Glu-1 loci. Two major genotypes of HMW-GS: 1, 13+16, 2+12 and 1, 6.1+22.1, 2+12 were found to occur in Central European spelt wheat cultivars and landraces at higher frequencies of 35 and 28%, respectively. The Glu-B1 locus displayed the greatest variation and genetic diversity index (H) was 0.69 whereas Glu-A1 and Glu-D1 showed H index values of 0.26 and 0.19, respectively. The dendrogram constructed by HMW and LMW glutenin subunit bands revealed that European spelts form a separated cluster from common wheat suggesting that spelt and common wheat form distinct groups. In addition, all 15 Iranian spelt land variety accessions differed from European spelts and possessed similar HMW-GS alleles to common wheat. Because of a wider polymorphism Central European spelt wheats are an important genetic reserviour for improving common wheat quality. Both authors contributed equally to this work