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.     

Distribution of the Rht-B1b, Rht-D1b and Rht8 reduced height genes in autumn-sown Chinese wheats detected by molecular markers

Reduction of plant height has played a significant role in improving wheat production and knowledge of dwarfing genes in Chinese wheat will be very important for developing high yielding cultivars. Molecular markers were used to detect the presence of genes Rht-B1b (Rht1), Rht-D1b (Rht2) and Rht8 in 220 wheat genotypes from autumn-sown wheat regions in China. They include landmark landraces, leading cultivars and core parents involved in wheat breeding from the 1950s to the present. Results indicated that Rht-D1b and Rht8 dominate with frequencies of 45.5% and 46.8%, respectively, followed by Rht-B1b with a frequency of 24.5%. The frequencies of Rht-B1b and Rht-D1b increased, from 8.6 to 32.2% and 36.2 to 53.4%, respectively, whereas the frequency of Rht8 has remained constant over time, when compared with cultivars released before and after 1990. This indicates that both the Rht-B1b and Rht-D1b were successfully used in wheat production in Chinese environments. Our study shows that Rht-B1b and Rht-D1b can be used in the post-anthesis heat stressed environments. Rht-B1b in Chinese wheats is derived from two sources, viz., Norin 10 and the Italian introduction St2422/464 (Rht-B1b and Rht8). The identity of Rht-B1b in these two sources still needs to be confirmed. Suwon 86 carrying both Rht-B1b and Rht-D1b, and Chinese cultivars, Huixianhong and Yaobaomai, are the primary sources of Rht-D1b in Chinese wheats. It is likely that Rht-D1b in Youbaomai derives from an unknown introduction. Italian introductions such as Funo and Abbondanza, and Lovrin 10 with the 1B/1R translocation, and Chinese landraces are the three major sources of Rht8. This information will be very valuable for wheat breeding in China, and internationally.     

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.     

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.     

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.     

Effect of Rht Alleles on the Tolerance of Wheat Grain Set to High Temperature and Drought Stress During Booting and Anthesis

Factorial pot experiments were conducted to compare the responses of GA‐sensitive and GA‐insensitive reduced height (Rht) alleles in wheat for susceptibility to heat and drought stress during booting and anthesis. Grain set (grains/spikelet) of near‐isogenic lines (NILs) was assessed following three day transfers to controlled environments imposing day temperatures (t) from 20 to 40 °C. Transfers were during booting and/or anthesis and pots maintained at field capacity (FC) or had water withheld. Logistic responses (y = c/1+e^{‐b(t ‐m)}) described declining grain set with increasing t, and t₅ was that fitted to give a 5 % reduction in grain set. Averaged over NIL, t₅ for anthesis at FC was 31.7 ± 0.47 °C (S.E.M., 26 d.f.). Drought at anthesis reduced t₅ by <2 °C. Maintaining FC at booting conferred considerable resistance to high temperatures (t₅ = 33.9 °C) but booting was particularly heat susceptible without water (t₅ = 26.5 °C). In one background (cv. Mercia), for NILs varying at the Rht‐D1 locus, there was progressive reduction in t₅ with dwarfing and reduced gibberellic acid (GA) sensitivity (Rht‐D1a, tall, 32.7 ± 0.72; Rht‐D1b, semi‐dwarf, 29.5 ± 0.85; Rht‐D1c, severe dwarf, 24.2 ± 0.72). This trend was not evident for the Rht‐B1 locus or for Rht‐D1b in an alternative background (Maris Widgeon). The GA‐sensitive severe dwarf Rht12 was more heat tolerant (t₅ = 29.4 ± 0.72) than the similarly statured GA‐insensitive Rht‐D1c. The GA‐sensitive, semidwarfing Rht8 conferred greater drought tolerance in one experiment. Despite the effects of Rht‐D1 alleles in Mercia on stress tolerance, the inconsistency of the effects over background and locus led to the conclusion that semidwarfing with GA‐insensitivity did not necessarily increase sensitivity to stress at booting and flowering. In comparison with effects of semidwarfing alleles, responses to heat stress are much more dramatically affected by water availability and the precise growth stage at which the stress is experienced by the plants.     

Effects of a photoperiod-response gene Ppd-D1 on yield potential and drought resistance in UK winter wheat

Using a pair of near-isogenic lines(NILs) of winter wheat (Triticumaestivum L.) contrasting for the Ppd-D1 and ppd-D1 alleles, in eachof Mercia and Cappelle-Desprez, experimentsin two seasons (1997/8 and 1998/9) on aloamy medium sand examined differences inflowering date, resource capture, biomassproduction and grain yield responses toirrigation. Drought did not occur for anysustained period in unirrigated conditionsin 1998 due to high seasonal rainfall. In1999, drought developed post-floweringunder unirrigated conditions. Ppd-D1on average advanced flowering by 12 days inMercia and 9 days in Cappelle-Desprez.Earlier flowering with Ppd-D1 was dueto a shorter thermal duration from cropemergence to GS31, with no effect on thethermal duration from GS31 to GS61. In bothgenetic backgrounds, Ppd-D1 decreasedabove-ground dry matter (AGDM) at harvestin irrigated conditions by 0.3–0.9 tha^-1 (p< 0.05), but thiswas compensated for by increases inharvest index (HI), so that grain yield wasconserved. Although Ppd-D1 decreasedmaximum green area index (GAI) by 0.8–1.9this was countered by greater maintenanceof green area after flowering, so thatradiation interception during grain fillingwas conserved. The Ppd-D1 alleledecreased season-long crop water uptake inthe Mercia NILs in irrigated conditions by39 mm. Effects of drought in 1999,averaging across NILs, were todecrease machine-harvested grain yield by 0.6 t ha^-1 in Mercia and by 1.8 tha^-1 in Cappelle-Desprez (p<0.05). The Ppd-D1 and ppd-D1NILs, though, responded similarly todrought in both genetic backgrounds. Earlyflowering with Ppd-D1 decreasedpre-flowering water uptake underunirrigated conditions by ca. 25 mm,but increased post-flowering uptake by only10 mm, compared to ppd-D1. This was aresult of smaller season-long water uptakefor Ppd-D1 compared to ppd-D1.Ppd-D1 decreased stem solublecarbohydrate measured shortly afterflowering under drought by ca. 0.3 tha^-1. Effects of Ppd-D1 onother drought-resistance traits, such aswater-use efficiency (WUE; AGDM per unitcrop evapotranspiration) and maximumrooting depth, appeared to be neutral. Itis concluded that the effects of the Ppd-D1 allele appeared to be largelyneutral on yield potential and late-seasondrought resistance in the UK's temperateenvironment in these genetic backgrounds.However, there were indications that Ppd-D1 may offer scope for breeding winterwheat cultivars with more efficientproduction of grain DM per unit seasonalcrop evapotranspiration, associated withimproved HI, compared to currentlycommercial UK genotypes.     

Use of non‐adapted quantitative trait loci for increasing Fusarium head blight resistance for breeding semi‐dwarf wheat

Semi‐dwarf wheat is an important prerequisite for releasing a successful commercial cultivar in high‐yielding environments. In Northern Europe, this aim is achieved by using one of the dwarfing genes Rht‐B1 (formerly known as Rht‐1) or Rht‐D1 (Rht‐2). Both genes, however, result in a higher susceptibility to Fusarium head blight (FHB). We analysed the possibility to use the two non‐adapted FHB resistance quantitative trait loci Fhb1 and Fhb5 (syn. QFhs.ifa‐5A) to counterbalance the negative effect of the dwarfing allele Rht‐D1b in a winter wheat population of 585 doubled‐haploid (DH) lines segregating for the three loci. All lines were inoculated with Fusarium culmorum at four locations and analysed for FHB severity, plant height, and heading date. The DH population showed a significant (p < 0.001) genotypic variation for FHB severity ranging from 3.6% to 65.9% with a very high entry‐mean heritability of 0.95. The dwarfing allele Rht‐D1b reduced plant height by 24 cm, but nearly doubled the FHB susceptibility (24.74% vs. 12.74%). The resistance alleles of Fhb1 and Fhb5 reduced FHB susceptibility by 6.5 and 11.3 percentage points, respectively. Taken all three loci together, Fhb5 alone was already able to reduce FHB susceptibility to the same extent as Rht‐D1b increased it. This opens new avenues for selecting semi‐dwarf wheat by marker‐assisted introgression of Fhb5 without the enhancement of FHB susceptibility.     

Allelic variation, sequence determination and microsatellite screening at the XGWM261 locus in Chinese hexaploid wheat (Triticum aestivum) varieties

Wheat microsatellite XGWM261, due to its closely linked to the dwarfing gene Rht8, has been adopted as the diagnostic molecular marker of Rht8. Screening 408 Chinese and 98 exotic varieties showed 13 allele variants in locus of XGWM261, with 6 alleles only to be found in Chinese varieties and 2 only in exotic varieties, respectively. Sequencing results of the 13 alleles revealed their absolute fragment sizes with 216, 212, 210, 206, 204, 202, 200, 196, 194, 192, 190, 174, and 164 bp, respectively. Allelic distribution analysis showed that the 204, 192, 174, and 164 bp alleles were prevailing in Chinese varieties, and the diagnostic 192 bp allele to Rht8 had a very high percentage in the Yellow and Huai River Valleys Facultative Wheat Zone than in the Northern Winter Wheat Zone in China. The GT → AC substitution at position 35 was found in 216, 200, and 174 bp alleles. Moreover, the AG insertion immediately at the end of CT-repeat region was also found in 216, 200, 174, and 164 bp alleles.     

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.     

Pleiotropic Effects of Genes for Reduced Height (Rht) and Day-Length Insensitivity (Ppd) on Yield and its Components for Wheat Grown in Middle Europe

Under field conditions in Germany over three growing seasons the pleiotropic effects on yield and its components of four sets of near isogenic lines carrying the GA insensitive dwarfing alleles Rht1, Rht2, Rht3, Rht1+2, Rht2+3 or rht (tall) in four different genetical backgrounds were examined together with 24 single chromosome recombinant lines segregating for the GA sensitive dwarfing gene Rht8 and the gene for day-length insensitivity Ppd1 in a ‘Cappelle-Desprez’ background. For the GA insensitive semi-dwarfs it was shown that in all three years a higher number of grains per ear was accompanied by a lower grain weight. Depending on the climatic conditions in a particular year, the increase in grain number was sufficient to compensate for the reduction in grain size and resulted in higher yields. For the Ppd1 allele yield advantages were found for wheats grown under environmental conditions of middle Europe.     

Light interception and radiation use efficiency in temperate quinoa (Chenopodium quinoa Willd.) cultivars

Sea level quinoas are grown at low altitudes in Central and Southern Chile. Both sensitivity to photoperiod and response to temperature largely determine quinoa adaptation, but crop biomass production must be quantified to evaluate agronomic performance. The objectives of this work are: (i) to characterize development effects on leaf area evolution for genotypes of sea level quinoa differing in cycle length, (ii) to quantify the extinction coefficient (k) for photosynthetically active radiation (PAR) and radiation use efficiency (RUE) from emergence up to the beginning of grain filling and (iii) to identify which crop attributes related to canopy architecture should be considered to improve biomass production. Four cultivars (NL-6, RU-5, CO-407 and Faro) were cropped in Pergamino (33°56′S, 60°35′W, 65 m a.s.l.), Argentina, at three densities (from 22 to 66 plants m⁻²) in two consecutive years under field conditions with adequate water and nutrient supply. Thermal time to first anthesis and maximum leaf number on the main stem were linearly correlated (r² = 0.87; p < 0.0001). Leaf area continued to increase during the flowering phase, notably in NL-6, the earliest genotype. There were significant differences in maximum plant leaf area between cultivars. Increasing density reduced plant leaf area but effects were comparatively small. Estimated k was 0.59 ± 0.02 across genotypes and was higher (p < 0.05) for 66 plants m⁻². Values for RUE changed as cumulative intercepted PAR (IPAR) increased; at initial stages of development RUE was 1.25 ± 0.09 g MJ IPAR⁻¹, but if cumulative IPAR was higher than 107.5 ± 10.4 MJ IPAR m⁻², RUE was 2.68 ± 0.15 g MJ IPAR⁻¹. That change occurred when leaf area index (LAI) and fraction of PAR intercepted were still low and ranged from 0.61 to 1.38 and from 0.33 to 0.51, respectively. No significant association was found with any developmental stage. Our results agreed to the notion that RUE variation during pre-anthesis phases is largely determined by LAI through its effect on radiation distribution within the canopy. Biomass production could be improved if periods of interception below 50% of incoming PAR were reduced to ensure high RUE. This seems to be possible in temperate areas both by the use of late genotypes with a higher number of leaves on the main stem and by early genotypes provided adequate plant density is chosen. Early increment in LAI and overlapping of the leaf area increase period with the flowering phase are desirable strategies for earliest genotypes to maximize yield.     

Wheat Rht‐B1 Dwarfs Exhibit Better Photosynthetic Response to Water Deficit at Seedling Stage Compared to the Wild Type

Wheat reduced height (Rht) genes encode modified DELLA proteins, which are gibberellin insensitive, accumulate under stress, restrain growth and affect plant stress response. The seedling reaction to soil water deficit regarding leaf gas exchange and chlorophyll fluorescence was compared in near‐isogenic lines carrying the alleles Rht‐B1a (tall), Rht‐B1b (semi‐dwarfing) and Rht‐B1c (dwarfing) and was related to leaf water content and anatomy. Under drought, Rht‐B1c line was characterized by less decreased CO₂ assimilation, delayed non‐stomatal limitation of photosynthesis and higher instantaneous water use efficiency. The functional state of its photosynthetic apparatus was better preserved as evidenced by the less decreased actual quantum yield (Φ_PSII) and potential maximum quantum yield (F_v/F_m) of PSII, and the less increased quantum yield of non‐regulated energy dissipation (Φ_NO). Rht‐B1b line also tended to perform better than Rht‐B1a, but differences were less pronounced. Although the leaves of both dwarf lines were smaller, thicker and more pubescent, their water content was not higher in comparison with the tall line. Nevertheless, in Rht‐B1c, leaf thickness was less decreased and mesophyll cells were less shrunk under drought. The more effective performance of the photosynthetic machinery of dwarf lines under water deficit could be explained by a combination of morpho‐anatomical and metabolic characteristics.     

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.     

四倍体小麦地方品种矮蓝麦矮秆性状的遗传分析

四倍体圆锥小麦(Triticum turgidum L.ssp.turgidum)地方品种矮蓝麦是我国重要的小麦矮秆基因资源,经鉴定其矮秆特性对外源赤霉酸敏感。2012年配制矮蓝麦与2个高秆圆锥小麦的正反交组合,2012—2013年在四川绵阳分别种植F1、F2代和F2:3家系,对株高的遗传分析表明,矮蓝麦的矮秆性状受1对隐性基因控制。利用BSA法构建高秆和矮秆池筛选多态性SSR标记,并对矮蓝麦/青稞麦F2分离群体进行连锁分析,将目标基因定位于7AS染色体上,与标记GWM471的遗传距离为2.5 c M。矮蓝麦与矮秆番麦正反交的F1和F2群体表现非常相似的株高变异特征,初步推测矮蓝麦的矮秆基因是Rht22;进一步用高通量SNP和DAr T标记对两品种进行全基因组扫描,发现二者的遗传相似性高达98.7%~99.3%。因此认为,历史上矮蓝麦和矮秆番麦可能是同一品种,是通过人为交流而传播到不同地方。矮蓝麦携带的矮秆基因在人工合成六倍体小麦遗传背景中降低株高能力中等或较弱,在育种中需要聚合其他矮秆基因而被利用。     

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.     

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.     

An assessment of the potential of 4DS.4DL-4s l L translocation lines as a means of eliminating tall off types in semi-dwarf wheat varieties

Summary Wheat varieties tend to be chromosomally unstable producing on average 2–3% of plants with abnormal chromosome numbers. A number of semi dwarf wheat varieties, carrying the gibberellic acid insensitive dwarfing genes Rht1 or Rht2, have been seen to produce distinct tall off types due to reduction in dosage of the chromosome carrying the dwarfing gene. The UK variety Brigand, carrying Rht2 on chromosome 4D, produced very distinct tall off types when this chromosome was reduced in dosage. The frequency of tall off types was sufficiently high to cause the variety to fail United Kingdom statutory uniformity tests. An attempt to prevent the loss of chromosome 4D was made by constructing translocation chromosomes involving the short arm of chromosome 4D, which carries Rht2, and the long arm of chromosome 4S ^l from Aegilops sharonensis, which carries a gene(s) conferring preferential transmission. The work in this paper describes the field evaluation of two lines carrying 4DS.4DL-4S ^l L translocations, and demonstrates their success in preventing spontaneously occurring monosomy of chromosome 4D in semi-dwarf wheats.     

Chromosomal location of dwarfing gene Rht12 in wheat

Summary The chromosomal location of the dwarfing gene Rht12 in the mutant winter wheat Karcagi 522M7K was investigated using F₂ monosomic analysis. The segregation ratio for F₂ progenies of Chinese Spring monosomics × Karcagi 522M7K, and that of Cheyenne monosomics × Karcagi 522M7K indicated that the near complete dominant dwarfing gene Rht12 is located on chromosome 5A. The heterozygous and hemizygous states of the genes Rht12 have the same effect on plant height.