Foliage‐applied sodium nitroprusside and hydrogen peroxide improves resistance against terminal drought in bread wheat

Terminal drought is threatening the wheat productivity worldwide, which is consumed as a staple food by millions across the globe. This study was conducted to examine the influence of foliage‐applied stress signalling molecules hydrogen peroxide (H₂O₂; 50, 100, 150 μm ) and nitric oxide donor sodium nitroprusside (SNP; 50, 100, 150 μm ) on resistance against terminal drought in two bread wheat cultivars Mairaj‐2008 and BARS‐2009. These stress signalling molecules were applied at anthesis stage (BBCH 61); drought was then imposed by maintaining pots at 35% water holding capacity. Terminal drought caused significant reduction in grain yield of both tested bread wheat cultivars; however, foliage application of both stress signalling molecules at either concentration improved the performance of both bread wheat cultivars. Maximum improvement in 100‐grain weight (12.2%), grains per spike (19.7%), water‐use efficiency (WUE; 19.8%), chlorophyll content index (10.7%), total soluble phenolics (21.6%) and free leaf proline (34.3%), and highest reduction in leaf malondialdehyde contents (20.4%) was recorded when H₂O₂ was foliage‐applied at 100 μm . Foliage application of SNP enhanced the grains per spike, 100‐grain weight and grain yield by 14.9%, 11.3% and 20.1%, respectively, than control. The foliage‐applied stress signalling molecules improved the accumulation of soluble phenolics, proline and glycine betaine with simultaneous reduction in malondialdehyde contents, which enabled wheat plants to sustain the biological membranes under stress resulting in better stay green (high chlorophyll contents) under drought. This helped improving the grain number, grain weight, grain yield, WUE and transpiration efficiency. In crux, foliage‐applied H₂O₂ and SNP, at pre‐optimized rate, may be opted to lessen the drought‐induced yield losses in bread wheat in climate change conditions.     

Application of natural plant extracts improves the tolerance against combined terminal heat and drought stresses in bread wheat

Drought and heat are among the main abiotic stresses causing severe damage to the cereal productivity when occur at reproductive stages. In this study, ten wheat cultivars were screened for combined heat and drought tolerance imposed at booting, heading, anthesis and post‐anthesis stages, and role of the foliage applied plant extracts was evaluated in improving the performance of differentially responding wheat cultivars under terminal heat and drought stresses. During both years, wheat crop was raised under ambient temperature and 70% water holding capacity (WHC) till leaf boot stage. The plant extracts (3% each) of sorghum, brassica, sunflower and moringa were foliage applied at booting, anthesis and post‐anthesis stage; and after one week of application of these plant extracts, combined heat and drought was imposed at each respective stage. Heat and drought stresses were imposed at each respective stage by placing pots in glass canopies with temperature of 4 ± 2°C above than the ambient temperature in combination with drought stress (35% WHC) until maturity. Combination of drought and heat stresses significantly reduced the performance of tested wheat cultivars; however, stress at the booting and heading stages was more damaging than the anthesis and post‐anthesis stages. Cultivars Mairaj‐2008 and Chakwal‐50 remained green with extended duration for grain filling, resulting in the maintenance of number of grains per spike and 100‐grain weight under stress conditions and thus had better grain yield and water‐use efficiency. However, in cultivars Fsd‐2008, and Shafaq‐2006, the combined imposition of drought and heat accelerated the grain filling rate with decrease in grain filling duration, grain weight and grain yield. Foliar application of all the plant extracts improved the wheat performance under terminal heat and drought stress; however, brassica extract was the most effective. This improvement in grain yield, water‐use efficiency and transpiration efficiency due to foliage applied plant extracts, under terminal heat and drought stress, was owing to better stay‐green character and accumulation of more soluble phenolics, which imparted stress tolerance as indicated by relatively stable grain weight and grain number. In crux, growing of stay‐green wheat cultivars with better grain filling and foliage application of plant extracts may help improving the performance of bread wheat under combined heat and drought stresses.     

Exogenous application of allelopathic water extracts helps improving tolerance against terminal heat and drought stresses in bread wheat (Triticum aestivum L. Em. Thell.)

The allelopathic water extracts (AWEs) may help improve the tolerance of crop plants against abiotic stresses owing to the presence of the secondary metabolites (i.e., allelochemicals). We conducted four independent experiments to evaluate the influence of exogenous application of AWEs (applied through seed priming or foliage spray) in improving the terminal heat and drought tolerance in bread wheat. In all the experiments, two wheat cultivars, viz. Mairaj‐2008 (drought and heat tolerant) and Faisalabad‐2008 (drought and heat sensitive), were raised in pots. Both wheat cultivars were raised under ambient conditions in the wire house till leaf boot stage (booting) by maintaining the pots at 75% water‐holding capacity (WHC). Then, managed drought and heat stresses were imposed by maintaining the pots at 35% WHC, or shifting the pots inside the glass canopies (at 75% WHC), at booting, anthesis and the grain filling stages. Drought stress reduced the grain yield of wheat by 39%–49%. Foliar application of AWEs improved the grain yield of wheat by 26%–31%, while seed priming with AWEs improved the grain yield by 18%–26%, respectively, than drought stress. Terminal heat stress reduced the grain yield of wheat by 38%. Seed priming with AWEs improved the grain yield by 21%–27%; while foliar application of AWEs improved the grain yield by 25%–29% than the heat stress treatment. In conclusion, the exogenous application of AWEs improved the stay green, accumulation of proline, soluble phenolics and glycine betaine, which helped to stabilize the biological membranes and improved the tolerance against terminal drought and heat stresses.     

Alleviation of drought stress in maize by exogenous application of gibberellic acid and cytokinin

The study was conducted to investigate the ameliorative roles of GA₃ and CK on adverse effects of drought in maize. Drought stressed maize plants were applied with GA₃ and CK at 50, 100, and 150 mg L^?l as foliar spray at the vegetative and the reproductive stages. Plant height, internode length, stem diameter, leaf chlorophyll index, and dry matter production were significantly affected by drought. In most cases, GA₃ and CK significantly improved the depressed plant traits, but in varying degrees depending on the growth stage encountering hormones, and their types and concentrations. Both GA₃ and CK were found to be very effective in alleviating drought-imposed adverse effects on maize at the vegetative phase. Such alleviating effects varied depending on the concentration of the hormones. Application of CK at 150 mg L^?l was excellent resulting in a 106% yield advantage compared to drought stress and 79.9% increase relative to well-watered controls. Conversely, GA₃ at 50 mg L^?l performed well showing 78.8% increase in grain yield. However, both GA₃ and CK had very little effect on improving the depressed growth and yield attributes in maize at the reproductive phase. The relative yield advantages for the hormones were mainly attributed to improving the cob and seed-bearing capacity of drought-stressed maize plants.     

Transpiration response of two bread wheat lines differing in drought resilience and their backcross parent under dry-down conditions

Improving wheat productivity in drylands largely depends on how plants manage limited water resources. Using fraction of transpirable soil water threshold (FTSW_Th) and drought stress response function, we characterized the water conservation traits of two wheat multiple synthetic derivative lines (MSD53 and MSD345) which both contain introgressed segments from Aegilops tauschii but differ in drought resilience. The lines and their backcross parent, ‘Norin 61’, were subjected to dry-down conditions. MSD53 had a higher FTSW_Th for transpiration decrease than ‘Norin 61’ and MSD345. In terms of drought stress response function, MSD53 had the lowest threshold suction, suggesting a lower drought resilience capacity compared with MSD345. However, MSD53 exhibited an effective-water-use trait whereas MSD345 exhibited a water-saving trait under dry-down conditions. These results are consistent with the reported higher yield of MSD53 in comparison with MSD345 under drought stress in Sudan, and demonstrate that high FTSW_Th supports effective water use for improved agricultural productivity in drylands. The differences in water conservation traits between the two MSD lines may be attributed to variation in introgressed segments, which can be further explored for drought resilience breeding.     

近60年河北省冬小麦干旱风险时空规律

干旱是造成作物减产的主要自然灾害,开展作物干旱成因机制和时空特征研究,对于稳定区域粮食生产有重要意义。本研究基于河北省内18个国家标准气象站点1958—2016年的长时间序列观测资料,采用水分亏缺指数(CWDI)作为干旱评价指标,分析了近60年来河北省冬小麦的干旱风险时空格局;通过CWDI对不同气象因子的敏感性分析,进一步探究了冬小麦干旱的成因机制。研究表明,冬小麦生育期需水量和干旱风险呈先增后减再增加的特征,在拔节–抽穗阶段的干旱风险最高,其次是抽穗-成熟阶段。冬小麦全生育期间干旱等级以重旱和特旱为主,特别在其产量形成的关键生长中后期,河北省东南部黑龙港地区面临较高的旱灾风险。冬小麦干旱受降水、气温、湿度等多种因素的影响,其中影响最大的是降水;气温是影响冬小麦生育后期干旱程度的关键因子,伴随近几十年气候变化冬小麦生长期内温度明显升高,将增加冬小麦生长期的耗水量和灌溉需求。本研究揭示了气候变化影响下河北省冬小麦干旱风险的时空演变规律,识别出了干旱灾害的高风险区和关键生育期阶段,可为优化冬小麦灌溉管理和农田防灾减灾提供参考依据。     

Marker‐assisted backcross breeding for improvement of drought tolerance in bread wheat (Triticum aestivum L. em Thell)

Drought stress is presently a major productivity limiting factor in wheat. This study developed five wheat lines with inbuilt tolerance to drought stress using marker‐assisted backcross breeding (MABB) approach employing three linked quantitative trait loci (QTLs) in an initial population of 516 BC₁F₁ plants. The high‐yielding wheat cultivar ‘HD2733’ grown over last few years extensively in the eastern plains of India is largely sensitive to drought and is used as the recurrent parent. ‘HI1500’ released for water‐limiting conditions and carrying drought‐tolerant QTLs was used as donor parent. MABB lines were advanced using foreground and background selection, coupled with stringent phenotyping. We identified 29 lines that were homozygous for targeted QTLs in different combinations with background recovery range of 89.2%–95.4%. Further evaluation of selected lines for physiological traits and distinctness, uniformity and stability (DUS) characters under rainfed condition identified five potential varieties for national varietal evaluation programme in the zone. The report is first of its kind in implementing known QTLs for the development of drought‐tolerant wheat lines through MABB approach.     

干旱对不同品种小麦幼苗的生理生化胁迫以及外源5-氨基乙酰丙酸的缓解作用

黄淮主产区冬小麦生育期干旱灾害发生频繁,造成小麦苗期严重光合生理伤害。为探讨不同小麦品种光合特性对干旱胁迫的响应,以百农207,周麦18以及小麦新品种郑麦1860为材料,研究了干旱胁迫对不同品种小麦幼苗光合生理、抗氧化物酶、相关基因表达水平的影响以及外源ALA的干旱缓解作用。研究结果表明,干旱胁迫下郑麦1860具有较高的根干重和根冠比,与周麦18相比,抗旱能力较强的郑麦1860和百农207叶绿素含量的下降幅度、MDA含量的增加幅度、叶绿素荧光参数和光合作用参数的下降幅度相对较低,但SOD和CAT酶活性的增加幅度相对较大。同时,干旱胁迫显著增加了CAT、SOD-Cu/Zn、MnSOD和FeSOD抗氧化酶相关基因的转录表达水平,且增加程度与小麦的抗旱能力密切相关。外源ALA预处理能够通过对CAT、SOD-Cu/Zn和MnSOD的转录诱导,进一步提高干旱胁迫下SOD和CAT酶的活性,降低膜脂过氧化损伤程度,同时提高ATP酶的活性,缓解干旱对小麦光合生理的伤害。此外,本研究首次发现,小麦叶绿体光合机构相关psb28基因转录表达的维持也与不同品种的抗旱能力有一定联系,且受外源ALA预处理的显著诱...     

Independent and combined effects of heat and drought stress in the Seri M82 × Babax bread wheat population

Heat and drought are the most important wheat production constraints worldwide. The objectives of this research were to evaluate the independent and combined effects of drought and heat in SeriM82/Babax population. Genotypes showed 11, 38 and 52% losses in grain yield (YLD) in 2010–11 and 18, 25 and 48% in 2011–12 under heat, drought and combined stress, respectively. Seri M82 had higher YLD than Babax under heat and combined stress. Grain per spike and canopy temperature at vegetative stage (CTv) in irrigated, day to heading and CT at grain‐filling stage (CTg) in drought, CTg and thousand‐grain weight (TGW) in heat and in combined trials were the best predictors of YLD. Results indicated that due to genotype by environment interactions not all stress‐adaptive traits could be accumulated in a single genotype. In general, day to heading, CTg and grain weight are suggested as indirect selection criteria for increasing YLD under heat and drought stresses. In particular, CTg could be used as a rapid and effective criterion for screening a high number of genotypes.     

Survey and new insights in the application of PCR‐based molecular markers for identification of HMW‐GS at the Glu‐B1 locus in durum and bread wheat

Wheat, among all cereal grains, possesses unique characteristics conferred by gluten; in particular, high molecular weight glutenin subunits (HMW‐GS) are of considerable interest as they strictly relate to bread‐making quality and contribute to strengthening and stabilizing dough. Thus, the identification of allelic composition, in particular at the Glu‐B1 locus, is very important to wheat quality improvement. Several PCR‐based molecular markers to tag‐specific HMW glutenin genes encoding Bx and By subunits have been developed in recent years. This study provides a survey of the molecular markers developed for the HMW‐GS at the Glu‐B1 locus. In addition, a selection of molecular markers was tested on 31 durum and bread wheat cultivars containing the By8, By16, By9, Bx17, Bx6, Bx14 and Bx17 Glu‐B1 alleles, and a new assignation was defined for the ZSBy9_aF1/R3 molecular marker that was specific for the By20 allele. We believe the results constitute a practical guide for results that might be achieved by these molecular markers on populations and cultivars with high variability at the Glu‐B1 locus.     

Effect of VRN‐1 and PPD‐D1 genes on heading time in European bread wheat cultivars

The variation of the vernalization (VRN‐1) and photoperiod (PPD‐1) genes offers opportunities to adjust heading time and to maximize yield in crop species. The effect of these genes on heading time was studied based on a set of 245 predominantly spring cultivars of bread wheat from the main eco‐geographical regions of Europe. The genotypes were screened using previously published diagnostic molecular markers for detecting the dominant or recessive alleles of the major VRN‐1 loci such as: VRN‐A1, VRN‐B1, VRN‐D1 as well as PPD‐D1. We found that 91% of spring wheat cultivars contain the photoperiod sensitive PPD‐D1b allele. Photoperiod insensitive PPD‐D1a allele has been found mainly in southern region of Europe. For this region the monogenic control of vernalization by VRN‐B1 or VRN‐D1 dominant alleles is common, whereas in the remaining part of Europe, the combination of photoperiod sensitive PPD‐D1b allele with dominant VRN‐A1, VRN‐B1 and recessive vrn‐D1 alleles represents the most frequent genotype. Also, we revealed a significantly later (5–8 days) heading of the monogenically dominant genotypes at VRN‐B1 as compared to the digenic VRN‐A1 VRN‐B1 genotypes.     

Differential root responses in two cultivars of winter wheat (Triticum aestivum L.) to elevated ozone concentration under fully open‐air field conditions

The effect of elevated tropospheric ozone concentration [O₃] on root processes in wheat systems of different O₃ sensitivity is not well understood. Two wheat cultivars (cv. Y15 and YN19) with contrasting O₃ tolerance were grown in a fully open‐air O₃ enrichment platform for one season. We found that elevated O₃ (EO₃) (50% above the ambient O₃) significantly decreased the total biomass at all key growth stages and the yield of the O₃‐sensitive cultivar YN19 but did not affect those of the O₃‐tolerant cultivar Y15. EO₃ significantly decreased the root biomass of two wheat cultivars at the jointing and grain‐filling stages. EO₃ significantly decreased the root length, length density, surface area and volume of the two cultivars at the jointing stage but increased those of YN19 at the grain‐filling stage. EO₃ significantly increased the root activities (specific root respiration rates) of Y15 and YN19 at the jointing, heading and grain‐filling stages. EO₃ significantly decreased the contribution of fresh root respiration to soil respiration (CRS) of YN19 at the jointing stage but increased it at the heading stage; however, it did not change the CRS of Y15 at any growth stages. This study indicates that the effects of EO₃ on root morphology and activity varied among wheat cultivars, and suggest that we can breed O₃‐tolerant cultivars to maintain crop yield under higher [O₃] scenarios.     

Relationships between leaf morpho‐anatomy,water status and cell membrane stability in leaves of wheat seedlings subjected to severe soil drought

The impact of the genotype‐specific leaf morphological and anatomical characteristics on the ability of wheat plants to preserve leaf water balance and cell membranes stability under drought stress was investigated. Seedlings of six modern semi‐dwarf (carriers of Rht, Reduced height genes) and six old tall bread wheat varieties were subjected to soil drought by withholding watering for 6 days. Morpho‐anatomical traits (leaf area, perimeter, thickness, stomata and trichome density) of daily watered (control) plants were characterized by light microscopy, scanning and image analyses. The leaf water status in both control and stressed plants was determined by measuring the relative water content (RWC). The leaf cell membranes stability in stressed plants was estimated by conductometric determination of the membranes injury index. On average, the modern semi‐dwarf varieties had less leaf area and leaf perimeter, and less dissection index, a parameter characterizing the leaf shape. Under drought stress, the modern genotypes maintained better water balance evidenced by significantly higher leaf RWC and better‐preserved the cell membranes stability supported by significantly lower Injury index. The correlations between morpho‐anatomical traits in control plants and drought tolerance‐related traits showed that the higher the leaf dissection index (i.e. more oblong leaves), the greater the water loss and the leaf membrane damages after desiccation were. The effect of shape of the evaporating surface on the water loss was modelled using wet filter paper. Similar to plant leaves, the evaporation and, respectively, water loss from paper pieces of more oblong shape (i.e. higher dissection index) was more intensive. The elucidation of the impact of the leaf shape on transpiration might contribute to better understanding of the mechanisms used by plants to maintain water reserves during drought stress and could be a basis for developing of simple and fast screening methods aiding the selection of drought tolerant genotypes.     

Effects of photoperiod sensitivity genes Ppd‐B1 and Ppd‐D1 on spike fertility and related traits in bread wheat

Increasing grain yield is a key breeding goal in bread wheat. Several authors have suggested that a spike fertility index (SF), that is the quotient between grain number per unit spike (GNS) and spike chaff dry weight (SCDW), could be used as a yield‐related selection criterion, especially if molecular markers were available. Here, the effects of Ppd‐B1 and Ppd‐D1 genes on SFm, GNSm and SCDWm (measured at maturity) and the relationship between these variables were analysed in field experiments carried out during three crop seasons at Balcarce, Argentina, on an association mapping population of 100 bread wheat cultivars of diverse origin released in Argentina between 1927 and 2010. Results show that both Ppd‐B1 and Ppd‐D1 are associated with SFm with similar effects. Cultivars with insensitive alleles at both genes showed a mean SFm 9.2% greater than those with sensitive alleles at both genes; at each gene, difference in SFm between insensitive and sensitive alleles was ~4.5%. In turn, each gene showed a differential effect on GNSm and SCDWm, as Ppd‐B1 was more related to SCDWm, whereas Ppd‐D1 was only related to GNSm. Although more research needs to be carried out in order to ascertain the physiological pathway by which these genes affect spike fertility, this study represents a first approximation in order to elucidate the molecular and genetic basis underlying SF and related physiological traits.     

A decade of Tropical Legumes projects: Development and adoption of improved varieties,creation of market‐demand to benefit smallholder farmers and empowerment of national programmes in sub‐Saharan Africa and South Asia

This article highlights 12 years (2007–2019) of research, achievements, lessons learned, challenges and gaps in discovery‐to‐delivery research in legumes emanating from three projects, collectively called Tropical Legumes (TL) with a total investment of about US$ 67 million funded by the Bill & Melinda Gates Foundation. These projects were implemented by three CGIAR centres (ICRISAT, CIAT and IITA) together with 15 national agricultural research system partners in sub‐Saharan Africa and South Asia. The TL projects together with some of their precursors and complementary projects from other agencies, facilitated the development of 266 improved legume varieties and the production of about 497,901 tons of certified seeds of the target legume crops in the focus countries. The certified seeds have been planted on about 5.0 million ha by more than 25 million smallholder farmers in the 15 countries and beyond, producing about 6.1 million tons of grain worth US$ 3.2 billion. Furthermore, the projects also trained 52 next generation scientists that included 10 women, by supporting 34 Masters degrees and 18 PhD degrees.     

Effects of Short‐Term High Temperature on Photosynthesis and Photosystem II Performance in Sorghum

Gas exchange and chlorophyll a fluorescence transient were examined in leaves of sorghum at high temperatures. No changes were found in photosynthetic rate (Pn) and photosystem II (PS II) performance index on absorption base (PI(abs)) at 40 °C for 1 h. But transpiration rate was enhanced significantly, which served as a self‐protection response for dissipating heat. The Pn decreased significantly at 40 °C for 3 h, and the decrease became greater at 45 °C. Decrease in Pn mainly resulted from stomatal limitation at 40 °C for 3 h, whereas it was due to non‐stomatal limitation at 45 °C. Decline in PS II function indicated by the significant decrease in PI(abs), trapped energy flux and electron transport flux were responsible for the decrease in Pn at 45 °C. PS II reaction centre and oxygen‐evolving complex in the donor side were not affected at high temperatures, but electron transport in the acceptor side was sensitive to high temperature. The PS II function recovered completely 1 day after high temperature stress even as high as 45 °C, which is favourable for sorghum to meet the challenge of global warming. However, Pn did not completely recover possibly due to heat‐induced irreversible damage to CO₂ fixation process.     

Including root architecture in a crop model improves predictions of spring wheat grain yield and above‐ground biomass under water limitations

Although the root length density (RLD) of crops depends on their root system architecture (RSA), the root growth modules of many 1D field crop models often ignored the RSA in the simulation of the RLD. In this study, two model set‐up scenarios were used to simulate the RLD, above‐ground biomass (AGB) and grain yield (GY) of water‐stressed spring wheat in Germany, aiming to investigate the impact of improved RLD on AGB and GY predictions. In scenario 1, SlimRoot, a root growth sub‐model that does not consider the RSA of the crop, was coupled to a Lintul5‐SlimNitrogen‐SoilCN‐Hillflow1D crop model combination. In scenario 2, SlimRoot was replaced with the Somma sub‐model which considered the RSA for simulating RLD. The simulated RLD, AGB and GY were compared with observations. Scenario 2 predicted the RLD, AGB and GY with an average root mean square error (RMSE) of 0.43 cm/cm³, 0.59 t/ha and 1.03 t/ha, respectively, against 1.03 cm/cm³, 1.20 t/ha and 2.64 t/ha for scenario 1. The lower RMSE under scenario 2 shows that, even under water‐stress conditions, predictions of GY and AGB can be improved by considering the RSA of the crop for simulating the RLD.     

Identification and mapping of adult‐plant stripe rust resistance in soft red winter wheat cultivar ‘USG 3555’

Little is known about the extent or diversity of resistance in soft red winter wheat (Triticum aestivum L.) to stripe rust, caused by the fungal pathogen Puccinia striiformis f.sp. tritici. The soft red winter (SRW) wheat cultivar ‘USG 3555’ has effective adult‐plant resistance to stripe rust, which was characterized in a population derived from ‘USG 3555’/‘Neuse’. The mapping population consisted of 99 recombinant inbred lines, which were evaluated for stripe rust infection type (IT) and severity to race PST‐100 in field trials in North Carolina in 2010 and 2011. Genome‐wide molecular‐marker screenings with 119 simple sequence repeats and 560 Diversity Arrays Technology (DArT) markers were employed to identify quantitative trait loci (QTL) for stripe rust resistance. QTL on chromosomes 1AS, 4BL and 7D of ‘USG 3555’ explained 12.8, 73.0 and 13.6% of the variation in stripe rust IT, and 13.5, 72.3 and 10.5% of the variation in stripe rust severity, respectively. Use of these and additional diagnostic markers for these QTL will facilitate the introgression of this source of stripe rust resistance into SRW wheat lines via marker‐assisted selection.