Inheritance of nitrogen and phosphorus utilization efficiency in spring barley at the vegetative growth stages under high and low nutrition

Inheritance of the nitrogen and phosphorus utilization efficiencies (NUE and PUE, respectively) and that of the tolerance (T) to limited NP nutrition was investigated in spring barley crosses at the vegetative growth stages. Plants were grown in sand-vermiculite cultures under high and low NP nutrition. In a diallel set (Ps and F₂s), both general combining ability (GCA) and specific combining ability (SCA) effects were significant for the variation in NUE and PUE, while the variation in T was mainly associated with GCA effects. The contribution of nonadditive genes for the utilization efficiencies was found to increase under nutrient shortages. Overdominance of genes was detected. The characters exhibited low heritabilities (0.10-0.42). Generation means analysis in two cross-combinations revealed significant effects of epistatic gene interactions. It was assumed that the involvement of both the dominance effects and epistatic interactions would not facilitate selection efforts to improve the characters in spring barley at its vegetative growth. Such selection should be performed among families of later generations. The genotype-nutrition interactions observed suggest that selection under diverse nutrition rates would be necessary for the more precise evaluation of barley efficiency under less favourable soil fertility.     

Inheritance of the efficiency of nitrogen uptake and utilization in winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) under diverse nutrition levels

The effects of contrasting soil nitrogen (N) levels on the inheritance of the efficiency of N uptake and N utilization in grain mass formation were examined in winter wheat. Parents of various origins and their diallel F₂-hybrids were evaluated in field and pot experiments under varying levels of soil N. The range of additive variance in the components of N efficiency was narrow, especially under N shortage. The soil N-treatments imposed had a substantial influence on gene actions responsible for the efficiency components and modes of inheritance. Genotype × nutrition interactions were common. Under high N-fertilization, the efficiency components were inherited in a manner favourable for wheat selection (preponderance of additive effects). However, the enhanced contribution of non-additive gene effects and increased dominance under N-limited conditions could impede wheat selection to improve the N efficiency and adaptation to less luxurious fertilization regimes. Selection methods that eliminate masking non-additive influences and take advantage of the additive variance should be employed to improve these traits.     

甘蔗近缘属植物氮磷钾养分效率的变异分析

为了筛选养分高效甘蔗种质资源及培育养分高效甘蔗品种,采用系统聚类分析法,分别以地上部干重,植株N、P、K素吸收效率和利用效率为指标,将40份具有代表性的甘蔗近缘属植物进行了分类。结果表明,甘蔗近缘属植物地上部干重变幅为1.26~39.6 kg/穴,变异系数为75.92%。云南82-85地上部干重是象草82-21的40.78%,但云南82-85的N、P、K素利用效率分别是象草82-21的4.9、1.7和3.2倍。不同类型甘蔗近缘属植物的地上部干重,N、P、K素营养效率的极差很大,可分为若干组,各组间差异显著,且同组内材料的N、P、K素营养效率之间也存在显著性差异。上述研究结果对选育营养高效的新型种质和阐明营养高效的生理机制具有一定参考价值。     

Application of quantitative trait locus mapping to the development of winter-habit malting barley*

Malting quality and winter-hardiness in barley are ‘ultimate’ phenotypes composed of constituent quantitatively inherited traits. A synthesis of molecular-marker linkage data and field phenotyping to reveal the location of quantitative trait loci (QTL) may assist in the development of winter-habit malting barley varieties. One-hundred doubled haploid progeny from a winter x spring cross were evaluated under fall and spring-planted conditions. Malting quality phenotypes and a 76-point map were used to identify QTL and to assess the effect of spring-and autumn-sowing on QTL expression. Many QTL effects were common to both environments and corresponded to QTL detected in other barley germplasm. While there were significant differences in the magnitude of effects across environments, there were no changes in the favourable allele phase. QTL effects for grain protein and diastatic power level coincided with the locations of known function genes. Coincident QTL for a number of mailing-quality traits on chromosome 7 suggests either the presence of a multi-locus cluster of genes controlling components of malting quality or a regulatory gene or genes controlling the cascade of enzymatic processes that function during the malting process. Based on these results, simultaneous selection for malting quality and cold tolerance should be possible in this genetic background.     

Genetic analysis of resistance in barley to barley yellow dwarf virus

The inheritance of resistance to barley yellow dwarf virus (BYDV) was studied in the selected 24 spring and winter barley cultivars that showed a high or intermediate resistance level in 1994‐97 field infection tests. The polymerase chain reaction diagnostic markers YLM and Ylp were used to identify the resistance gene Yd2. The presence of the Yd2 gene was detected with both markers in all the resistant spring barley cultivars and lines from the CIMMYT/ICARDA BYDV nurseries. The results of field tests and genetic analyses in winter barley corresponded with marker analyses only when the Ylp marker was used. Genes non‐allelic with Yd2 were detected by genetic analyses and the Ylp marker in moderately resistant spring barley cultivars ‘Malvaz’, ‘Atribut’ and ‘Madras’, and in the winter barley cultivars ‘Perry’ and ‘Sigra’. Significant levels of resistance to BYDV were obtained by combining the resistance gene Yd2 with genes detected in moderately resistant cultivars. The utilization of analysed resistance sources in barley breeding is discussed.     

The influence of nitrogen and phosphorous status on glyphosate hormesis in Lemna minor and Hordeum vulgare

The herbicide glyphosate has been shown to stimulate growth and photosynthetic capacity of barley and other plant species. The growth increase, however, only takes place under certain, yet undefined, growth conditions. We hypothesise that glyphosate growth stimulation only takes place, when growth is nutrient limited. Nutrient limitation was induced in this study by limiting nitrogen and phosphorous availability. The experiments were performed on hydroponically grown lesser duckweed and barley and on barley in the field. Hydroponic duckweed and barley grown under a range of N- and P-availabilities displayed glyphosate induced growth increases in plants which were slightly stressed by N-deficiency, but not in response to P-deficiency in the case of barley. The growth increase found for P-deficient duckweed was hypothesised to be caused by glyphosate derived P, acting as a nutrient source. No growth increase was found in the 2012 field experiment, which was in contrast to earlier year’s findings. Our hypothesis that nutrient limitation makes plants susceptible to glyphosate induced growth was only confirmed for nitrogen but not for phosphorous and not under field conditions in 2012. Mechanisms related to high C:N ratios might be of importance, as this trait varies depending on N- and P-availability during plant growth.     

稻种资源苗期氮素营养效率的分类、鉴定与评价

在低氮(20 mg/kg)、中氮(40 mg/kg)和高氮(60 mg/kg)3个水平下，调查了88份稻种资源的苗期性状并测定了氮素营养效率，包括氮素利用效率(NUE)、氮素吸收效率(NAE)和氮素利用效率响应度(NUER)。结果表明，苗期不同性状对低氮、中氮和高氮的敏感性不同，不同氮素水平间的单株根体积、地上部干重、吸氮量和根干重等性状变异较大，低氮胁迫加大了种质间的差异。不同水稻苗期性状对氮素的响应度不同，性状在种质间的变异服从正态分布。通过分类、 鉴定和评价，供试稻种资源分为13种氮素营养效率类型，它们存在明显的基因型差异，呈典型的正态分布，即低效和高效的较少，以NUE、NAE和NUER中效类型最多。NUE、NAE和NUER三指标间还存在很强的互补性和拮抗性，极少存在两个以上指标同为低效或高效的稻种资源类型。水稻氮素营养效率类型较陆稻丰富，但分布较分散，总体分布明显偏向于低氮素利用效率一侧。籼稻氮素营养效率的类型略多于粳稻，而粳稻类型的总体分布明显偏向于低氟素利用效率一侧。地方晶种氮素营养效亭类型较多、分布较集中，总体分布明显偏向于高氮素利用效率一侧：杂交稻氟素营养效率的类型最少、分布最集中，而常规稻氮素营养效率类型最多、分布较分散，常规稻和杂交稻品种的总体分布明显偏向于低氮素利用效率一侧。上述研究结果对探讨稻种资源蓖素营养效率的遗传特性、选育高效氮素营养的新型种质及阐明高效氮素营养的生理机制等具一定参考价值。     

Relationship of Carbon Isotope Discrimination to Water Use Efficiency and Productivity of Barley Under Field and Greenhouse Conditions

This study was conducted to evaluate the application of carbon isotope discrimination (CID) as a selection criterion for improving water use efficiency (WUE) and productivity of barley (Hordeum vulgare L.) under field and drought‐stress conditions in a greenhouse. A total of 54 genotypes were screened for variability in CID under field conditions, while 23 genotypes were evaluated under water‐deficit conditions in the greenhouse. A survey of leaf CID of 54 genotypes at two field locations showed more than 2.14‰ difference between extreme genotypes. Significant (P ≤ 0.05) genotypic variation was found in WUE and CID that had a negative strong correlation. There was a negative correlation between leaf CID and aerial biomass in the greenhouse and among six‐row genotypes in the field. Correlations between leaf CID across field locations and across irrigation regimes in the greenhouse were significant (experiment 1, r = 0.79 and 0.94 for six‐ and two‐row genotypes), suggesting stability of the CID trait across different environments. Overall, these results indicate the potential of leaf CID as a reliable method for selecting for high WUE and productivity in barley breeding programmes in the Canadian prairies. Further work is currently underway to determine heritability/genetics of leaf CID and application of molecular marker‐assisted selection for the traits in barley breeding programmes.     

Generation mean analysis of phosphorus‐use efficiency in freely nodulating soybean crosses grown in low‐phosphorus soil

Freely nodulating soybean genotypes vary in their phosphorus (P) uptake and P‐use efficiency (PUE) in low‐P soils. Understanding the genetic basis of these genotypes’ performance is essential for effective breeding. To study the inheritance of PUE, we conducted crosses using two high‐PUE genotypes, two moderate‐PUE genotypes and two inefficient‐PUE genotypes, and obtained F₁, F_2, BC₁ and BC₂ populations. The inheritance of PUE was evaluated using a randomized complete block design. A generation mean analysis of phenotypic data showed that PUE was heritable, with complex inheritance patterns and the presence of additive, dominance and epistatic gene effects. Seed P, shoot P, root P, P‐incorporation efficiency and PUE were largely quantitatively inherited traits. There were dominance, additive × additive and dominance × dominance gene effects on PUE, grain yield, shoot dry weight, 100‐seed weight, root dry weight and shoot dry matter per unit P for populations grown under low‐P conditions. Dominance effects were generally greater than additive effects on PUE‐related indices. These PUE indices can be used to select P‐efficient soybean genotypes from segregating populations.     

Waterlogging severely retards P use efficiency of spring barley (Hordeum vulgare)

Efficient utilization of various phosphorus (P) sources for producing optimum yields in P‐deficient conditions requires knowledge of best management under changing weather conditions. In this study, barley (Hordeum vulgare) was grown in an extremely P‐deficient soil with variable moisture conditions. During a wet growing period, utilization of P from dairy cow manure (DCM), fox manure (FM) and meat and bone meal (MBM) was compared with the utilization of P from superphosphate (SP) with concomitant effects on grain yield and quality. High P application rates were necessary to compensate for severe yield losses due to waterlogging. Only 7 kg P/ha was required for optimum yield in less waterlogged conditions, while 43 kg P/ha was needed in waterlogged conditions. In both moisture conditions, broadcast DCM‐P increased grain yield similar to banded SP‐P, although P acquisition was lower in early growth stages. FM‐P and MBM‐P were less efficiently utilized. Waterlogging also depressed yield quality when P was applied. Extreme rainfall events are predicted to become more frequent at northern latitudes. As an alternative to higher P fertilizer rates, improving soil drainage could be a favourable, long‐term measure for better utilization of applied P and soil P resources, even at very low soil P status.     

江苏滨海盐碱地麦后直播棉氮、磷、钾肥料优化配比研究

【目的】建立江苏省滨海盐碱地麦后直播棉合理的施肥技术体系。【方法】2017―2018年在江苏省滨海棉田,以中棉所50为材料,采用正交设计,研究了不同氮、磷、钾肥配施量对棉花生物量、养分累积与利用及产量的影响。【结果】氮、磷、钾肥3因子对棉株地上部和生殖器官生物量、棉株地上部氮和钾素累积量及皮棉产量的影响均为氮肥>磷肥>钾肥。施N 150~225 kg·hm-2、P2O575 kg·hm-2下棉株地上部和生殖器官生物量、氮和钾累积量及皮棉产量较高。钾肥因子对生殖器官生物量和皮棉产量影响不显著。钾肥因子对氮、钾素利用效率的影响大于氮肥和磷肥,氮肥因子对磷素利用效率的影响大于磷肥和钾肥,施K2O 75~150 kg·hm-2氮、钾素利用效率较高、施氮225 kg·hm-2磷素利用效率较高。土壤碱解氮、速效磷、速效钾含量较高棉田的氮、磷(P2O5)、钾(K2O)肥配施量分别为225 kg·hm-2、75 kg·hm-2和150~225 kg·hm-2。相关分析表明,皮棉产量与棉株氮、钾素累积量显著正相关。【结论】长江流域棉区滨海盐碱地麦后直播棉利于产量和养分利用效率提高的最佳氮、磷(P2O5)、钾(K2O)肥配施量分别为225 kg·hm-2、75 kg·hm-2、75 kg·hm-2。     

Genetic regulation of growth and nutrient content under phosphorus deficiency in the wild barley introgression library S42IL

Phosphorus (P) is an important macronutrient required for plant growth and yield formation. Since decades, breeders aim to optimize P efficiency in crops. We studied a set of 47 wild barley (Hordeum vulgare ssp. spontaneum, Hsp) introgression lines (ILs) in hydroponic culture to identify quantitative trait loci (QTLs) improving growth and nutrient content under P deficiency. Applying a mixed model analysis, a total of 91 independent QTLs were located among 39 ILs, of which 64 QTLs displayed trait‐improving Hsp effects. For example, an unknown Hsp allele on barley chromosome 4H increased shoot dry weight under P deficiency in three overlapping ILs by 25.9%. Likewise, an Hsp allele on barley chromosome 6H increased root dry weight under P deficiency in two overlapping ILs by 27.6%. In total, 31 QTLs confirmed Hsp effects already identified in previous field and glasshouse experiments with the same ILs. We conclude that wild barley contains numerous trait‐improving QTL alleles, which are active under P deficiency. In future, the underlying genes can be subjected to cloning and, simultaneously, used in elite barley breeding.     

Genetic basis of grain filling rate in wheat (Triticum aestivum L. emend. Thell.)

Summary Grain filling rate in wheat (Triticum aestivum L. emend. Thell.) positively influences grain yield under a wide range of conditions. The effective utilization of this trait in breeding depends on an understanding of its genetic control. A study was, therefore, conducted to determine the genetic basis of grain filling rate in six crosses of wheat. Higher order genic interactions and/or linkage were important in the genetic regulation of grain filling rate (GFR) in the majority of crosses. Additive ([d]) and dominance ([h]) gene effects were important in the control of GFR in main ears (ME) and whole plant ears (WPE). Additive and additive × additive epistatic effects were the most important in the genetic control of GFR in last ears (LE). Location effects on genetic effects for GFR were significant (P < 0.05) in all ear types of some crosses except in ME. Genotype × environment interaction effects were important (P < 0.001) in LE and WPE.It was concluded that the inheritance of GFR is complex and is dependent on ear type. Breeding procedures that facilitate the exploitation of non-additive and additive gene effects were recommended for the genetic improvement of grain filling rate of wheat.     

Diallel analysis of barley for resistance to leaf stripe and impact of the disease on genetic variability for yield components

Barley breeders in Syria attempting to develop barley (Hordeum vulgare L.) cultivars resistant to barley leaf stripe (BLS) disease caused by Pyrenophora graminea Ito & Kuribayashi [anamorph Drechslera graminea (Rabenh. Ex. Schlech. Shoem.)]. Information on the combining ability for BLS resistance in Syria is not available. This study was conducted to evaluate, in 10 genetically diverse barley parents, general combining ability (GCA) and specific combining ability (SCA) effects towards the determination of the genetic basis of disease resistance and to estimate genetic variability for yield components and its modification by BLS. Ten parental genotypes varying in their reactions to BLS were crossed in a half-diallel mating design to generate 45 full-sib families. The families and the parents were inoculated with P. graminea and evaluated for resistance in replicated field tests (three inoculated and three non-inoculated plots). The parents chosen showed wide variations for resistance to BLS. Genetic component analysis showed significant effects for both GCA and SCA for resistance to BLS, suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. GCA effects were more important than SCA effects. Resistant parents exhibited high negative GCA indicating that additive gene effects were more predominant, and suggesting their prime suitability for use in barley breeding programs to improve resistance to BLS. Narrow-sense heritability was 58% and broad-sense heritability was 99% indicating that selection for BLS resistance should be effective in these crosses. A high genetic variability for the agronomic traits studied was observed. Yield components decreased significantly in inoculated plants and more pronounced in diseased plants. Significant GCA was observed for all traits. Values for GCA were, in some cases, significantly modified by BLS. This indicates that attention must be paid to the danger of drawing conclusion in quantitative genetics studies dealing with both diseased and healthy plants. Two genotypes, Banteng and Igri, had high negative GCA effects and are promising parents for enhancement of BLS resistance.     

Efficiency in the use of phosphorus,nitrogen and potassium in topless faba beans (Vicia faba L.) – variability and inheritance*

In a field experiment with topless faba beans, parental inbred lines and FI hybrids of a 7 × 7-diallel were evaluated for traits related to the P, N and K efficiency. In addition, the parental inbreds were cultivated in a pot experiment at two P levels (100 vs. 700 mg P per pot). Significant heterosis for grain yield, uptake and utilization efficiency of nutrients in the field experiment highlighted the enhancement of nutrient efficiency in the hybrids. Amongst both parental inbreds and hybrids, significant genotypic variation was found for nearly all recorded traits. In the diallel analysis, the GCA effects generally proved to be highly significant and in most cases considerably higher than the SCA effects. In the pot experiment, grain yield ranking of the parental lines at the high P level (= P700) was very similar to that in the field experiment, whereas at the low P level (= P100, – P deficiency) the ranking of the lines changed considerably. Correspondingly, the P level-line interaction was highly significant. High tolerance towards P deficiency was found for those two parental inbreds derived from cultivars bred under Syrian conditions. At the high P supply, P efficiency was more favoured by a high P uptake, but at P deficiency by a high internal P utilization.     

Photosynthetic Acclimation to Cold as a Potential Physiological Marker of Winter Barley Freezing Tolerance Assessed under Variable Winter Environment

Winter‐hardiness is a complex trait limiting cultivation of winter barley (Hordeum vulgare ssp. vulgare) with respect to the regions of temperate climate. In the present studies, we verified whether inexpensive and fast physiological markers characterizing photosynthetic acclimation to cold may provide robust characteristics of winter barley genotypes for improved frost resistance. Freezing tolerance of 28 winter barley varieties and advanced breeding lines were tested for three winters in field‐laboratory experiment and under fully controlled conditions. To increase the environmental variability of freezing tolerance, a part of the plants were also de‐acclimated under semi‐controlled conditions and re‐acclimated in laboratory before freezing tests. After controlled cold acclimation, apparent quantum yield of photosystem II (F_v/F_m) as well as photochemical (q_P) and non‐photochemical (NPQ) coefficients of chlorophyll fluorescence quenching were studied. Field‐laboratory method assessment of freezing tolerance gives distinct and even opposite results in subsequent years. Also de‐acclimation interacted with growth conditions in the field, giving different rankings of genotypes each year. The results obtained suggest that high level of freezing tolerance measured in laboratory, which is connected with photosynthetic acclimation to cold may be not sufficient for the expression of field resistance, especially when winter conditions are not favourable for cold acclimation.     

Leaf Photosynthesis During Grain Filling Under Mediterranean Environments: Are Barley or Traditional Wheat More Efficient Than Modern Wheats?

Barley is one of the most popular crops in dryland agricultural systems of Mediterranean areas, where it is assumed that barley, or traditional wheat cultivars, performs better than modern wheat under low‐yielding conditions. It was tested whether variations in net leaf photosynthetic rate (P_N) during grain filling provide any basis for the potential better performance of barley and traditional wheat compared to modern wheats in Mediterranean areas. Two groups of field experiments were conducted in Agramunt (NE Spain) during 2005/06 (06) and 2006/07 (07) growing seasons combining low and high nitrogen (N) availabilities under rain‐fed and irrigated conditions. Cultivars used in the first group of experiments were a traditional (Anza) and a modern (Soissons) wheat, whilst in a second group of experiments, a wheat (Soissons) and a barley (Sunrise) modern cultivars were used. Both wheat cultivars showed a similar P_N during grain filling but higher than that of the modern barley cultivar. Differences between species in P_N were maximized under high‐yielding conditions. There were no differences between cultivars in instantaneous water‐use efficiency. The barley cultivar showed a higher specific leaf area, but lower N content per unit of leaf area, than wheat. Photosynthetic nitrogen‐use efficiency was similar between the traditional and the modern cultivar but lower than barley. Decreases in P_N after anthesis were not exactly observable in SPAD measurements. In conclusion, we found no consistent differences between cultivars in terms of post‐anthesis photosynthetic activity to support the assumption of better performance under Mediterranean farm conditions of traditional wheat or barley against modern wheat.     

Rph23: A new designated additive adult plant resistance gene to leaf rust in barley on chromosome 7H

We report on a new adult plant resistance (APR) gene Rph23 conferring resistance to leaf rust in barley. The gene was identified and characterized from a doubled haploid population derived from an intercross between the Australian barley varieties Yerong (Y) and Franklin (F). Genetic analysis of adult plant field leaf rust scores of the Y/F population collected over three successive years indicated involvement of two highly additive genes controlling APR, one of which was named Rph23. The gene was mapped to chromosome 7HS positioned at a genetic distance 36.6 cM. Rph23 is closely linked to marker Ebmac0603, which is flanked by markers bPb‐8660 and bPb‐9601 with linkage distances of 0.8 and 5.1 cM, respectively. A PCR‐based marker was optimized for marker‐assisted selection of Rph23, and on the basis of this marker, the gene was postulated as being common in Australian and global barley germplasm. Pedigree and molecular marker analyses indicated that the six‐rowed black Russian landrace ‘LV‐Taganrog’ is the likely origin of Rph23.     

水稻剑叶角度与氮素营养效率的关系

剑叶角度是构成水稻理想株型的重要指标和影响水稻产量的重要因素。通过水稻剑叶角度与氮营养效率的关系研究,为水稻塑造理想株型和提高氮营养效率提供理论依据与技术途径。试验采用盆栽土培法,以不同年代的9个典型稻种资源为材料,设置不施氮（0 kg/hm²尿素）、正常施氮（240 kg/hm²尿素）和高施氮（480 kg/hm²尿素）3个施氮水平,于水稻灌浆期测量剑叶角度、各器官含氮量和土壤含氮量,进行剑叶角度与氮营养效率间的相关分析与函数拟合。结果表明,不同水稻品种的剑叶角度和氮营养效率存在显著的基因型差异,且随施氮水平而异。剑叶角度随施氮量的增加而急剧增加,不施氮下的基因型间差异明显小于正常施氮和高施氮。剑叶角度与氮利用效率、土壤氮生产力、植株氮生产力和氮收获指数呈显著负相关,不同氮营养效率间存在极显著正或负相关。氮利用效率、土壤氮生产力、植株氮生产力和氮收获指数随剑叶角度呈显著的对数递减,顺序为植株氮生产力＞氮收获指数＞氮利用效率＞土壤氮生产力。因此,在生产上可根据水稻剑叶角度来预测氮营养效率,并以其为依据实时地调控氮肥运筹来实现氮营养的高效利用。     

Changes over time in the adaptation of barley releases in north-eastern Spain

The objective of this study was to characterize grain yield and adaptation of barley cultivars released in recent decades in north-eastern Spain. Ten six-rowed and 10 two-rowed barley genotypes were grown in eight environments. Mean yields varied among environments between 1.7 and 5.8 tha^?1. New releases showed higher mean yields and were specifically adapted to nonlimiting growing conditions. The average genetic advances were estimated as 40.7 and 32.9 kg ha^?1 years^?1 for two- and six-rowed genotypes, respectively, in the four most productive environments. Old genotypes, with lower overall grain yields, were specifically adapted to the poorer sites. A negative genetic gain, estimated as -14.8kg ha^?1 years^?1. was reorded for six-rowed culiivars in the four poorest sites. No significant association was observed between heading date and year of release. Variations in carbon isotope discrimination (Δ) were examined to assess whether changes in adaptation could be partially explained by shifts in the genoiypic transpiration efficiency (TE) over time, in the most favourable environments, new releases showed the highest grain yields and carbon isotope discrimination values (Δ). By contrast, older cultivars had constitutively? lower Δs and therefore higher TEs. These results suggest a genetic association between low TE and yield potential and specific adaptation to stress-free conditions so that selection for yield under favourable conditions could have resulted in an indirect downward genetic shift in the TE of modern cultivars.