Designing resilient and sustainable grasslands for a drier future: Adaptive strategies,functional traits and biotic interactions

In many regions of the world, such as Southern Europe and most Mediterranean areas, the frequency and magnitude of droughts and heat waves are expected to increase under global warming and will challenge the sustainability of both native and sown grasslands. To analyze the adaptive strategies of species, genotypes and cultivars, we aim both (i) to understand the composition and functioning of natural grasslands and (ii) to propose ideotypes of cultivars and optimal composition for mixtures of species/genotypes under water deficit and high temperatures. This review presents a conceptual framework to analyze adaptive responses of perennial herbaceous species, starting from resistance to moderate drought with growth maintenance (dehydration avoidance and tolerance of lamina) to growth cessation and survival of plants under severe stress (dehydration avoidance and tolerance of meristems). The most discriminating functional traits vary according to these contrasting strategies because of a trade-off between resistance to moderate moisture deficit and survival of intense drought. Consequently it is crucial to measure the traits of interest in the right organs and as a function of soil water use, in order to avoid misleading interpretations of plant responses. Furthermore, collaboration between ecologists, eco-physiologists, and agronomists is required to study the combination of plant strategies in natural grasslands as only this will provide the necessary rules for species and cultivars or ecotypes assemblage. This ‘agro-ecological’ approach aims to identify and enhance functional complementarity and limit competition within the multi-specific or multi-genotypic material associated in mixtures since using plant biodiversity should contribute to improving grassland resistance and resilience.     

Breeding for adaptation to drought and heat in cowpea

Accomplishments in breeding for adaptation to drought and heat are reviewed based upon work with the indeterminate grain legume species cowpea. Plant traits and some crop management methods are examined that influence adaptation to rainfed production in the drought-prone, semiarid tropical Sahelian zone of Africa. Drought escape, drought resistance, delayed-leaf-senescence, and varietal intercrops are examined. In addition, adaptation to the heat that can detrimentally impact irrigated production in the hot, subtropical arid zone of California is evaluated. Heat tolerance during reproductive development, electrolyte leakage, membrane thermostability, some aspects of crop management including date of sowing, and chilling tolerance during emergence including the beneficial effects of a dehydrin protein are considered. Methods for breeding cowpeas with adaptation to drought and heat are described that have been effective.     

甘蓝型油菜耐盐和耐旱相关性状的QTL分析

盐胁迫和干旱胁迫是非生物胁迫中影响作物产量的重要因素,检测与耐盐和耐旱相关的QTL,可为抗逆油菜品种的选育提供理论依据。本研究利用德国冬性甘蓝型油菜Express和中国半冬性甘蓝型油菜SWU07为亲本构建的包含261个株系的双单倍体(doubled haploid, DH)群体,分别以1.2%NaCl溶液和20%PEG-6000溶液作为培养液模拟盐胁迫和干旱胁迫,去离子水为对照,对2个亲本和DH群体进行发芽试验。播种后7 d测定幼苗根长、鲜重及发芽率,计算各性状在盐胁迫和干旱胁迫下的相对值,并作为评价耐盐和耐旱的指标。根据已构建的遗传连锁图谱进行QTL定位。盐胁迫下,在3次重复中共检测到与盐胁迫相关的QTL12个,分布在A02、A03、A05、A09、C01和C09染色体上,单个QTL可解释的表型变异为3.61%～10.59%,其中5个QTL在不同的重复中被检测到。干旱胁迫下,共检测到与干旱胁迫相关的QTL 9个,分布在A01、A02、A03、A05、A09、A10和C03染色体上,单个QTL可解释的表型变异为3.94%～12.90%,其中2个QTL在不同的重复中被检测到。此外,在A0...     

Etiolated growth in relation to energy reserves and winter survival in three temperate grasses

The role of energy reserves in development of winter hardiness was examined in timothy (Phleum pratense L.), orchardgrass (Dactylis glomerata L.) and perennial ryegrass (Lolium perenne L.) through periodically measuring etiolated growth (EG; shoot growth of crown under dark, warm and humid conditions following defoliation) and determining sugar profiles at critical stages of hardening and wintering. Seasonal changes in weight and duration of EG were monitored by sampling once or twice a month from September to the following April. In all species, total etiolated growth (TEG; total shoot production at each sampling time as determined by weekly or biweekly harvests until exhaustion of reserves) increased from September to reach peak levels during the second hardening stage in mid-November. Thereafter, TEG remained high until the following spring in orchardgrass while it declined linearly in timothy, which had the lowest TEG. The decline in TEG was intermediate in perennial ryegrass. Changes in the duration of EG were most marked in orchardgrass, as it required six weeks to produce about 150 mg g^-1 TEG in early November but only one week in March. The results indicated occurrence of dormancy in apical meristems of orchardgrass at the end of the first hardening stage with temperatures above 0 ^°C, which roughly corresponded with the phase of dormancy in woody plants. Dormancy was weak in timothy and largely undetectable in perennial ryegrass, as measured by the EG technique. A positively significant correlation between total nonstructural carbohydrates (TNC) content and TEG was found in all species. Detailed analysis, however, showed that direct estimation of TNC content using TEG was difficult because TEG production per unit TNC was negatively correlated with TNC level, and the amount of TNC unused in early autumn was more than in the rest of the season. Changes in sugar profiles occurred at transition from the first to the second hardening stage with subzero temperatures and varied with wintering strategy of each species. Simple sugar content dramatically declined while fructan content increased in both timothy (cv. ‘Senpoku’) and orchardgrass (cv. ‘Wasemidori’), which were selected at sites covered with snow for more than 120 days. In contrast, a cold tolerant perennial ryegrass cv. `‘éveille’ selected in the Netherlands retained high amounts of simple sugars. The results suggest that EG technique is suitable to monitor physiological status (amount and rate of mobilization of energy reserves, intensity of dormancy and bud development) of plants expressing winter hardiness. This revised version was published online in July 2006 with corrections to the Cover Date.     

20年来我国冬油菜新品种产量和抗病性状分析

根据近20年来我国冬油菜区域试验的结果,对长江上、中、下游及黄淮4组油菜新品种产量性状及抗病性状进行分析,结果表明,冬油菜新品种平均产量整体呈上升趋势,各组平均单株有效角果数变化不明显,而平均每果粒数和千粒重呈上升趋势,但长江流域各组每角粒数增量比黄淮组大,而黄淮组千粒重增量比长江流域各组高;新品种菌核病和病毒病发病率下降明显。今后一段时间内增加新品种每角粒数和千粒重是冬油菜遗传改良的重点,预计我国冬油菜新品种区域试验各组新品种产量水平仍将继续提高。     

陆地棉株型性状对皮棉产量的遗传贡献分析

为阐明陆地棉主要株型性状对皮棉产量的贡献,采用加性-显性及与环境互作的遗传模型,利用估算条件方差分量和预测条件遗传效应值的统计方法对9个陆地棉品种（系）及其F1代20个组合皮棉产量和9个株型性状的2年资料进行了贡献分析。结果表明,9个株型性状对皮棉产量的表型贡献率分布在0.1%~11.1%之间。主茎节距、始果枝高、果节数对皮棉产量具有显著或极显著的加性遗传贡献率,分别为29.8%、6.2%和5.7%,果枝夹角对皮棉产量的加性遗传方差具有较大的抑制作用（-39.9%）;果节数对皮棉产量的显性遗传方差贡献率最高（57.8%）;主茎节距对皮棉产量有极显著的加性×环境互作遗传方差贡献率（17.7%）,其它株型性状对皮棉产量的加性×环境互作遗传方差、显性×环境互作遗传方差的贡献率较小或不显著。亲本2和4的果节数、亲本3、5和6的始果枝高、亲本7的主茎节距对其皮棉产量有最大的加性贡献,表明对皮棉产量加性效应贡献最大的株型性状因不同亲本而异。多数杂交组合皮棉产量的显性效应主要受果节数的影响,因此,果节数可作为间接选择皮棉产量显性效应的指标。     

Morpho-physiological traits to complement grain yield selection under semi-arid Mediterranean conditions in each of the durum wheat types mediterraneum typicum and syriacum

Summary Some 238 landraces from Algeria and Tunisia representative of the mediterraneum typicum durum wheat type and 265 landraces from Syria and Jordan representing the syriacum type were grown in a semi-arid Mediterranean environment of Northern Syria characterized by moderate drought stress. The germplasm types were compared for mean value, level of variation and relationships with grain yield of various morpho-physiological traits possibly usable for indirect selection of best yielding materials. The syriacum germplasm showed higher yield mainly due to greater earliness of cycle, slightly longer grain filling period, shorter stature, lower early growth vigour and higher drought tolerance expressed by a visual score recorded in another, more stressful environment in the region. It also showed lower variation for all morpho-physiological characters except plant glaucousness, for which it was more variable. The wheat types differed not only for architecture but also for optima of individual morpho-physiological traits required to maximize the yield response in the given environment. Higher yield of syriacum materials was attained at same heading and three to four days delayed maturity with respect to average phenology of three well-adapted control cultivars, and it was favoured by increasing number of kernels per spike, early vigour and drought tolerance. Higher yield of mediterraneum typicum landraces was related to heading and maturity dates approaching those of the control cultivars and to increasing kernel weight, early vigour and drought tolerance. Plant stature hardly affected the yield. Both absent and strong glaucousness could confer a yield advantage in syriacum materials.     

Expression of the limited‐transpiration trait under high vapour pressure deficit in peanut populations: Runner and virginia types

Drought can be a critical limitation on peanut yield. A physiological trait that may help to ameliorate drought is limited transpiration (TR_lim), defined as a limitation on further increases in transpiration rate (TR) under high vapour pressure deficit (VPD) conditions. The advantage of the TR_lim trait is that it allows plant water conservation to increase soil water availability for use during late‐season drought. While this trait has been identified in peanut, there is no information of how readily the trait may be transfer to progeny lines. The objective of this study was to obtain preliminary information on the expression of the TR_lim trait in two peanut progeny populations. One population was runner type of 88 RILs derived from the mating of Tifrunner × NC 3033. The second set was selected for the virginia‐type phenotype of large pods obtained from mating of PI 585005 (ICGV 86015) and N0808olJCT, both of which expressed the TR_lim trait. A two‐tier screen was applied to both populations. The initial screen was based on exposure of de‐rooted shoots to silver ions. Fifteen runner type and 12 virginia type were selected for direct measures of transpiration response to varying VPD. The results from each of the two populations showed that an effective expression of the TR_lim trait occurred in about 30% of the progeny in each population. While these results do not offer a definitive index of inheritance, they do indicate that there appears to be a strong possibility of transferring the TR_lim trait to progeny genotypes.     

Evaluation of the contribution of teosinte to the improvement of agronomic,grain quality and yield traits in maize (Zea mays)

Teosinte, an ancestor to modern maize, displays an excellent performance regarding resistance to stress, but its yield potential has rarely been reported. To evaluate the potential contribution of teosinte to maize improvement, two maize–teosinte backcrossed recombination inbred line (RIL) populations and their corresponding test-cross hybrids were planted for trait assessment. In RN and ZP RIL populations, the average coefficients of variation of 31 agronomic traits were 9.14% (Range, 0.38%‒25.21%) and 6.85% (Range, 0.55%‒27.73%), respectively. The correlation coefficients of 13 common shared traits between RIL populations and test-cross hybrid populations ranged from 0.10 to 0.60 and from 0.06 to 0.72, respectively. A total of 39 and 3 recombined inbred lines, and 29 and 47 test-cross hybrids exhibited higher yields than their checks (RP125, Zheng58, CD189 and ZD958) with the BLUP data, respectively. Furthermore, four test-cross hybrids including RN034/SCML1950, ZP068/Chang7-2, ZP079/Chang7-2 and ZP122/Chang7-2 showed a more stable yield performance, with yield gains of +7.07%, +3.64%, +5.83% and +3.82% over checks, respectively. In conclusion, teosinte could serve as an alien germplasm for maize breeding.     

Hybrid performance of sorghum and its relationship to morphological and physiological traits under variable drought stress in Kenya

Sorghum, Sorghum bicolor L. Moench, is grown mostly in semi-arid climates where unpredictable drought stress constitutes a major production constraint. To investigate hybrid performance at different levels of drought stress, 12 single-cross hybrids of grain sorghum and their 24 parent lines were grown in eight site-season combinations in a semi-arid area of Kenya. In addition, a subset of 20 genotypes was evaluated at the seedling stage under polyethylene glycol (PEG)-induced drought stress. Environmental means for grain yield ranged from 47 to 584 g/m²reflecting the following situations: two non-stress, one moderate pre-flowering, four moderate terminal and one extreme drought stress. Mean hybrid superiority over mid-parent values was 54% for grain yield and 35% for above-ground biomass. Across environments, hybrids out-yielded two local varieties by 12%. Differences in yield potential contributed to grain yield differences in all stress environments. Early anthesis was most important for specific adaptation to extreme drought. Field performance was not related to growth reduction and osmotic adjustment under PEG-induced drought stress. In conclusion, exploitation of hybrid vigour could improve the productivity of sorghum in semi-arid areas.     

Quantitative trait loci mapping of freezing tolerance and photosynthetic acclimation to cold in winter two‐ and six‐rowed barley

Photoacclimation (PA) and freezing tolerance (FT) have been identified as closely related traits, due to common mechanisms of environmental control. In this study, diversity array technology (DArT) was used for identification of the quantitative trait loci (QTL) of FT and PA in winter barley. Simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers were subsequently used to saturate QTL regions. Two F₂ mapping populations were created, for two‐rowed (P44) and six‐rowed barley (CaP). Different regions of the genome were responsible for differences in traits between parents in these two populations. Eleven QTLs were identified in the P44 population, including five typical for FT and PA, on chromosomes 2H, 3H and 7H. In the CaP population, only one QTL connected with PA and 10 connected with FT were found on all chromosomes except 2H. Our results demonstrate that different sets of markers should be applied in marker‐assisted selection for FT in two‐ and six‐rowed barley, as several loci determine FT at the level of biparental crosses.     

冬小麦基因型离体叶片失水与产量结构和植株性状的关系

根据４年的研究结果,分析了在冬小麦基因型产量和株高变异较大时,离体叶片失水速率（ＲＷＬ）与产量构成和植株性状的关系,研究表明,ＲＷＬ基因型间存在显著差异。在多数情况下ＲＷＬ与产量和千粒重呈负相关,与株高呈正相关。研究还发现基因型位次随失水时间的变化,有低失水,先快后慢,先慢后快和高失水４种类型。ＲＷＬ与产量负相关随失水时间延长而减弱。基因型差异以失水２－３ｈ最为明显,且更具有较大生理意义,因此提出     

Mapping QTLs of traits contributing to yield and analysis of genetic effects in tetraploid cotton

Fiber yield and yield components – including lint index (LI), seed index (SI), lint yield (LY), seed cotton yield (SCY) and number of seeds per boll (NSPB) – were investigated on the farm of Huazhong Agricultural University in a population of 69 F₂ individuals and corresponding F_2:3 families derived from a cross between high-fiber-yield Gossypium hirsutum CV Handan 208 and a low-fiber-yield Gossypium barbadense CV Pima 90. On the basis of the genetic map constructed previously from the same population by Lin et al. (Plant Breed., 2005), quantitative trait locus (QTL) analysis was performed with the software QTL Cartographer V2.0 using composite interval mapping method (LOD ≥ 3.0). A total of 21 QTLs were identified, which were located in 15 linkage groups. The number of QTLs per trait ranged from one to seven. Of these QTLs detected, one affecting LI explained 24.3% of phenotypic variation (PV), five influencing SI explained 16.15–39.21% of PV, seven controlling LY explained 13.01–28.35% of PV, and two controlling SCY explained 22.76 and 39.97% of PV, respectively. Simultaneously, the detected six QTLs for NSPB were located on five linkage groups, which individually explained 28.01–38.32% of the total phenotypic variation. The results would give breeders further insight into the genetic basis of fiber yield.     

Tolerance to paraquat is correlated with the traits associated with water stress tolerance in segregating F2 populations of barley and wheat

To identify scorable marker traits that can be used in cereal breeding programs for selecting drought tolerant individuals, we investigated the correlation among the drought-associated traits in two F₂ populations derived from the crosses made between drought tolerant and sensitive barley and wheat parental genotypes. The parental genotypes of these crosses also differed by at least three other traits – paraquat tolerance, leaf size, and the relative water content. These three traits were scored in two F₂populations of 80 individuals for each barley and wheat cross. Analysis of results indicated that the enhanced tolerance to paraquat was correlated with reduced leaf size and increased relative water content, two traits associated with water stress phenotypes of the drought tolerant barley and wheat parents. Our results suggested that the selection based on paraquat tolerance istechnically less demanding and thus useful for rapid screening of individuals for enhanced drought tolerance in segregating populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

旱地冬小麦产量、氮肥利用率及土壤氮素平衡对降水年型与施氮量的响应

研究不同降水年型施氮量对旱地冬小麦产量、氮素利用及土壤氮素表观平衡的影响,探讨渭北旱塬旱作麦田稳产增效的最佳氮素投入量,为高效施氮提供理论依据。田间定位施氮试验于2017—2020年连续3年在陕西合阳县开展,以长6359为试验材料,设置5个施氮量处理包括0、60、120、180和240 kg hm^-2 (分别以N0、N60、N120、N180和N240表示),研究旱地冬小麦产量、氮肥利用率及土壤氮素平衡对降水年型与施氮量的响应。连续3年定位试验表明:(1)降水年型对冬小麦产量和经济收益影响显著,丰水年较平水年和欠水年分别增产33.6%和113.3%,经济收益提高2～3倍以上。冬小麦氮肥回收利用率和农学效率与产量有相似的变化规律,丰水年氮肥回收利用率和农学效率较平水年和欠水年分别提高4.7个百分点、0.6 kg kg–1 (平水年)和11.9个百分点、2.5 kg kg–1 (欠水年)。(2)无论何种降水年型,冬小麦产量、氮肥回收利用率和农学效率均随施氮量增加呈现先增加后下降的趋势。在丰水年和平水年,均以N180处理下最高,收获期0～100 cm土层土壤硝态氮积累分...     

不同株型小麦干物质积累与分配对氮肥响应的动态分析

为了揭示株型和施氮量对小麦干物质积累与分配动态的影响,通过实施不同株型小麦品种和氮肥处理的田间试验,于主要生育期测定了各处理单株及不同器官干物质积累量,并分别利用Richards和VP方程对其进行拟合。结果表明,适量施氮提高了各株型小麦的干物质平均增长速率(R_a)和最大增长速率(R_max),缩短了各株型小麦到达R_max的时间,延长了各株型小麦的缓增持续期(D₃)。施氮提高了紧凑型矮秆品种矮抗58、松散型品种淮麦17和中间型品种扬麦12的起始生长势(R₀),缩短了上述3种株型小麦的渐增持续期(D₁),降低了其到达R_max时的干物质积累量(W_Rmax),而紧凑型高秆品种宁麦9号的R₀、W_Rmax和D₁与上述3种株型小麦的变化趋势相反。随施氮量的增加,矮抗58和宁麦9号的快增持续期(D₂)呈下降趋势,而淮麦17和扬麦12的D₂以中氮处理(150 kg hm^-2)最低。施氮降低了淮麦17和扬麦12的叶、穗最大分配比例(P_max)以及矮抗58和宁麦9号的茎鞘最大分配比例(P_Smax),但增加了矮抗58和宁麦9号的叶部和穗部P_max以及淮麦17和扬麦12的P_Smax。施氮降低了宁麦9号、淮麦17和扬麦12的叶分配比例最大下降速率及矮抗58和宁麦9号的穗分配比例最大增长速率,而增加了矮抗58的叶分配比例最大下降速率及淮麦17和扬麦12的穗分配比例最大增长速率,但过量施氮抑制了宁麦9号穗分配比例最大增长速率的增加和扬麦12穗分配比例最大增长速率的下降。施氮对各株型小麦茎鞘分配比例最大增长和下降速率(R_Simax和R_Sdmax)的影响无明显规律。因此,在建立高产小麦栽培技术体系时,应充分考虑到不同株型小麦干物质积累和分配动态对施氮量的响应差异。     

Functional mechanisms of drought tolerance in maize through phenotyping and genotyping under well watered and water stressed conditions

Developing tolerant genotypes is crucial for stabilizing maize productivity under drought stress conditions as it is one of the most important abiotic stresses affecting crop yields. Twenty seven genotypes of maize (Zea mays L.) were evaluated for drought tolerance for three seasons under well watered and water stressed conditions to identify interactions amongst various tolerance traits and grain yield as well as their association with SSR markers. The study revealed considerable genetic diversity and significant variations for genotypes, environment and genotype × environment interactions for all the traits. The ranking of genotypes based on drought susceptibility index for morpho-physiological traits was similar to that based on grain yield and principal component analysis. Analysis of trait – trait and trait – yield associations indicated significant positive correlations amongst the water relations traits of relative water content (RWC), leaf water potential and osmotic potential as well as of RWC with grain yield under water stressed condition. Molecular analysis using 40 SSRs revealed 32 as polymorphic and 62 unique alleles were detected across 27 genotypes. Cluster analysis resulted in categorization of the genotypes into five distinct groups which was similar to that using principal component analysis. Based on overall performance across seasons tolerant and susceptible genotypes were identified for eventual utilization in breeding programs as well as for QTL identification. The marker-trait association analysis revealed significant associations between few SSR markers with water relations as well as yield contributing traits under water stressed conditions. These associations highlight the importance of functional mechanisms of intrinsic tolerance and cumulative traits for drought tolerance in maize.