Flag Leaf Senescence Research Articles

Identification and characterization of miRNAs during flag leaf senescence in rice by high-throughput sequencing

Flag leaf is the last leaf to senesce and its life span plays a critical role in determining grain quality and yield in rice. Little is known about the molecular changes that occur and their regulation in time-dependent manner during flag leaf senescence in rice. Several studies have explored different aspects of miRNA functions in plant development; however, a diminutive account is available about their role in flag leaf senescence. With an aim to unravel the role of miRNAs in ageing of flag leaf in rice, four small RNA libraries were prepared from three stages of senescence and sequenced by Illumina deep sequencing technology. Thirty-eight known and 494 novel miRNAs were identified in the senescing flag leaves. Digital expression analysis revealed that 21 known and 116 novel miRNAs were differentially expressed during senescence. Family member(s) of miR156, miR159, miR160, miR164, miR169, miR171, miR393, miR396, miR535, miR827, miR1428, miR1432 and miR1861 were differentially expressed in at least one stage of flag leaf senescence. The present study has generated a repository of senescence-related miRNAs that can be utilized to contemplate molecular approaches for manipulating the timing of flag leaf senescence in rice and other related crops.

Comparison of different mathematical models describing flag leaf senescence process of wheat and characteristics of leaf senescence process

Comparison of different mathematical models describing flag leaf senescence process of wheat and characteristics of leaf senescence process

The involvement of cytokinin and nitrogen metabolism in delayed flag leaf senescence in a wheat stay-green mutant, tasg1

In the present study on a wheat stay-green mutant, tasg1, we found that its delayed senescence at the late filling stage was related to the high cytokinin (CK) and N contents. RNA sequencing suggested that several genes may be responsible for the different senescence processes between wild-type (WT) and tasg1 plants. WT and tasg1 seedlings were treated with NH4NO3, lovastatin, and 6-benzylaminopurine (BAP), and the results suggested that the feedback of CK with N content regulated the leaf senescence in the tasg1 plants. Furthermore, a knock-out of the candidate gene cisZOGT1 (catalytic O-glucosylation in cis-zeatin) in the wheat mutant pool ‘Kronos’ exhibited delayed senescence at the late grain filling stage. Overall, our results suggested the cisZOGT1 gene has an important role in regulating wheat leaf senescence by regulating CK and N metabolism. At the same time, CK and N metabolism involved in delayed flag leaf senescence of tasg1 may be by a feedback pattern.

Optimized micro-sprinkling irrigation scheduling improves grain yield by increasing the uptake and utilization of water and nitrogen during grain filling in winter wheat

The North China Plain (NCP) is the main wheat production area in China; however, irrigation water and nitrogen fertilizer use in this area is relatively inefficient, and must be optimized to attain higher yield and resource use efficiency for winter wheat. In this study, a four-year field experiment was conducted during the 2012–2016 growing seasons. Under quota irrigation conditions, an experiment with various micro-sprinkling frequencies (S2, irrigation at jointing and anthesis; S3, irrigation at jointing, booting and filling; and S4, irrigation at jointing, booting, anthesis and filling) was conducted in 2012–2014. In 2014–2016, different nitrogen application rates (150, 195, and 240 kg N ha−1; denoted as S4N1, S4N2, and S4N3, respectively) under the S4 condition were tested. The local traditional flood irrigation pattern was designated as the control (CK) in 2012–2016. The grain yield, leaf area index of the population (LAI), flag leaf senescence during gain filling, accumulation and distribution of dry matter and nitrogen, and water and nitrogen use characteristics were investigated. The results showed that, no significant difference was observed in grain yield between the CK and S2, whereas S4 and S3 showed increased grain yields of 5.7–22.2% and 4.6–19.1%, respectively, compared with the CK. The increase of yield in micro-sprinkling treatments was mainly due to a significant increase in the 1000-grain weight. With increasing irrigation frequency, the LAI at the filling stage improved significantly; the flag leaf chlorophyll content decreased slowly; and the total dry matter accumulation, dry matter after anthesis, and its contribution to grain yield increased significantly. Meanwhile, the total water consumption of S4 (N2) decreased significantly, and the water use efficiency increased by 10.0–27.8% compared with the CK. In addition, micro-sprinkling irrigation with frequent application of a small amount of water with optimized nitrogen application (S4N2) yielded the highest nitrogen fertilizer use efficiency. Water consumption and nitrogen accumulation during grain filling were significantly increased in S4, which could explain the higher yield and resource use efficiency of S4. Overall, a suitable micro-sprinkling irrigation frequency (S4) and nitrogen application (195 kg N ha−1) can achieve higher grain yields and resource use efficiencies in the NCP.

Interactions between cytokinin and nitrogen contribute to grain mass in wheat cultivars by regulating the flag leaf senescence process

Premature senescence after anthesis reduces crop yields. Delaying leaf senescence could maintain photosynthetic activity for a longer period and lead to a higher photosynthetic rate. Recent studies have provided some insights into the interaction between cytokinin and nitrogen (N) in the regulation of plant development. In the present study, foliar application of exogenous 6-benzylaminopurine (6-BA) and lovastatin, an inhibitor of cytokinin synthesis, was combined with three N rates [0 kg ha−1 (low nitrogen, LN), 240 kg ha−1 (normal nitrogen, NN), and 360 kg ha−1 (high nitrogen, HN)] in two wheat cultivars, Wennong 6 (with a staygreen phenotype) and Jimai 20 (with a non-staygreen phenotype). Flag leaf senescence was assessed using a Gompertz growth curve. Grain mass, dry matter accumulation and distribution, total N of flag leaf, and concentrations of zeatin riboside (ZR) and abscisic acid (ABA) were also used to evaluate the functional characteristics of flag leaves. Grain mass was negatively correlated with initial senescence rate (r0) and duration of rapid chlorophyll loss (Chlloss), whereas it was positively correlated with maximum senescence rate (rmax), average senescence rate (raver), persistence phase (Chlper), total duration of flag leaf (Chltotal) and inflection point cumulative temperature (M). Compared to Jimai 20, Wennong 6 had larger raver, Chlper, and Chltotal. The concentration of ZR was highest under the 6-BA × NN treatment, followed by the 6-BA × HN and 6-BA × LN treatments. However, the concentration of ABA showed the opposite trend. It was concluded that the staygreen phenotype Wennong 6 was associated with greater grain mass and altered cytokinin metabolism and could be classified as a functional staygreen type. Foliar application of 6-BA interacting with N at the NN level (240 kg ha−1) may be a beneficial strategy for improving grain yield of wheat by regulating endogenous hormones and the flag leaf senescence process. Increasing endogenous cytokinin promoted the transport of dry matter to grain.

Ridge-furrow mulched with plastic film improves the anti-oxidative defence system and photosynthesis in leaves of winter wheat under deficit irrigation.

In semi-arid areas of China, the ridge-furrow mulched with plastic film (RF) cultivation system is a common water-saving agricultural technique where the shortage of water resources has become a serious problem. Therefore, we aimed to explore whether this cultivation is actually an improvement over the traditional flat planting (TF) method while testing two deficit irrigation (150, 75 mm) levels to grow winter wheat. Furthermore, we examined the responses of the anti-oxidative defence system and photosynthetic capacity of winter wheat flag leaves under three simulated rainfall (275, 200 and 125 mm) conditions. The results showed that the RF system with 150 mm deficit irrigation and 200 mm simulated rainfall condition (RF2150) treatment raised soil water content (%) at the jointing and flowering stages and achieved higher net photosynthesis rates (Pn) in flag leaves. Furthermore, such improvements were due to the reduction of malondialdehyde (MDA) content and oxidative damage during different growth stages of winter wheat. The RF2150 treatment significantly increased the activities of superoxide dismutase (SOD); peroxidise (POD), catalase (CAT) and ascorbate peroxidase (APX) and the content of soluble protein (SP) during different growth stages of winter wheat. Furthermore, RF2150 treatment attained the highest value at the flowering stage, while also exhibiting significant declines in contents of proline, MDA, H2O2 and O2 in flag leaves. The higher free H2O2 and O2 scavenging capacity and better anti-oxidative enzyme activities under the RF2150 treatment were due to the lower level of lipid peroxidation, which effectively protected the photosynthetic machinery. The net photosynthetic rate of flag leaves was positively correlated with SOD, POD, CAT, APX and SP activities, and negatively correlated with proline, MDA, H2O2 and O2 contents. We concluded that the RF2150 treatment was the better water-saving management strategy because it significantly delayed flag leaf senescence and caused the increases in SWC, WUE, Pn, antioxidant enzyme activities and grain yield of winter wheat grown in semi-arid regions of China.

Genetic variation in N-use efficiency and associated traits in Indian wheat cultivars

Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N2O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to quantify the genetic variability in N-use efficiency (NUE) in Indian spring wheat cultivars and identify traits for improved NUE for application in breeding. Twenty eight bread wheat cultivars and two durum wheat cultivars were tested in field experiments in two years in Maharashtra, India. Detailed growth analysis was conducted at anthesis and harvest including dry matter (DM) and N partitioning. Senescence of the flag leaf was assessed from a visual score every 3–4 days from anthesis to complete flag-leaf senescence and fitted against thermal time to estimate the onset and end of post-anthesis senescence. Grain yield (GY) was reduced under low N (LN) by an average of 1.46 t ha−1 (−28%). Significant N × genotype level interaction was observed for grain yield and NUE. Above-ground N uptake at harvest was reduced from 162 kg N ha−1 under high N (HN) to 85 kg N ha−1 under low N (LN) conditions, while N-utilization efficiency (grain DM yield per unit crop N uptake at harvest; NUtE) increased from 32.7 to 44.6 kg DM kg−1 N. Genetic variation in GY under LN related mainly to variation in N uptake at harvest rather than NUtE; and the N × genotype effect for GY was mainly explained by the interaction for N uptake at harvest. Averaging across years, the linear regression of onset of flag-leaf senescence on GY amongst cultivars was significant under both HN (R2 0.16. p < 0.05) and LN (R2 0.21, p < 0.05) conditions. Onset of flag-leaf senescence was positively associated with N uptake at anthesis under HN (R2 0.34, p < 0.001) and LN (R2 0.22, p < 0.01) conditions. Flag-leaf senescence timing was not associated with post-anthesis N uptake. It is concluded that increased N accumulation at anthesis was correlated with flag-leaf senescence timing and that N accumulation at anthesis is an important trait for enhancing grain yield and NUE of wheat grown under low to moderate N supply in India.

Validation of QTL for the Flag Leaf Senescence in Wheat Under Drought

Validation of QTL for the Flag Leaf Senescence in Wheat Under Drought

Reproductive sink enhanced drought induced senescence in wheat fertile line is associated with loss of antioxidant competence compared to its CMS line

Reproductive sinks regulate monocarpic senescence in wheat as desinking delayed flag leaf senescence under irrigated condition. In this study, wheat cv. HW 2041 and its isonuclear male sterile line (CMS) were subjected to post-anthesis water deficit stress to understand the association between sink strength, senescence and drought response in relation to oxidative stress and antioxidant defense at cellular and sub-cellular level. CMS plants maintained better water relations and exhibited delayed onset and progression of flag leaf senescence in terms of green leaf area, chlorophyll and protein content than fertile plants under water deficit stress (WDS). Delayed senescence in CMS plants under water deficit stress was associated with less reactive oxygen species generation, lower damage to membranes and better antioxidant defense both in terms of antioxidant enzyme activities and metabolite content compared to fertile plants. Expression of some senescence associated genes (SAGs) such as WRKY transcription factor (WRKY53), glutamine synthetase1 (GS1), wheat cysteine protease (WCP2) and wheat serine protease (WSP) was lower while catalse 2 (CAT2) transcript levels were higher in the CMS plants compared to HW2041 during senescence under water deficit stress. Antioxidant defense in chloroplasts was better in CMS line under water deficit stress compared to HW2041. This is the first report showing that reproductive sink enhanced drought induced senescence in flag leaf of wheat fertile line is associated with higher oxidative stress and damage and loss of antioxidant competence compared to its sterile line under water deficit stress. Higher expression of some SAGs and decline in superoxide dismutase and ascorbate peroxidase activity in the chloroplasts also contributed to the accelerated senescence in fertile line compared to its CMS line under WDS.

Analysis of Genetic Diversity among the Different Wheat (Triticum aestivum L.) Genotypes

Forty one wheat ( Triticum aestivum L. ) genotypes were studied for days to booting, days to heading, plant height at vegetative, plant height at maturity, days to 50% anthesis, days to 100% anthesis, flag leaf senescence, days to physiological maturity, peduncle length, effective tillers, spikelet’s length, grain per spike, biomass ,harvest index, sterility percentage, thousand grain weight and grain yield in random complete block design at terai, Nepal with the objective to identify superior genotypes after clustering them based on their genetic diversity in performance. Result of multivariable analysis revealed that 41 wheat genotypes formed four clusters. Cluster 4 and 2 had highest value of effective tiller, spike length, grain per spike, thousand grain weight, biomass, harvest index ,grain yield and lowest value days to heading, days to booting ,days to anthesis and sterility percentage. Cluster 3 had high days to booting, days to heading, days to 50% and 100% anthesis, days to flag leaf senescence and low in plant height at maturity, thousand grain weight ,harvest index and grain yield. Considering of multivariable analysis and other agronomic performance wheat genotypes HD 1982 and Pitic 62 may be utilized as high yielding genotypes in Terai condition of Nepal.

Relationship between Lipid and Flag Leaf Senescence Induced by Low Nitro-gen Stress during Grain Filling of Wheat

Relationship between Lipid and Flag Leaf Senescence Induced by Low Nitro-gen Stress during Grain Filling of Wheat

Late‐season photosynthetic rate and senescence were associated with grain yield in winter wheat of diverse origins

AbstractThere is a lack of studies that have investigated grain yield, its components and photosynthesis in late stages of wheat growth, giving us insufficient understanding of how these factors interact to contribute to yield during this period. As a result, three field experiments were carried out examining 20 winter wheat genotypes of diverse origins under irrigated, terminal drought and dryland conditions in the southern Idaho. Our objective was to evaluate the interaction between post‐anthesis physiological traits, especially leaf‐level photosynthetic capacity, senescence and yield components on grain yield in different moisture regimes. Genotype differences were found in leaf‐level photosynthesis and senescence, canopy temperature depression, grain yield and yield components in each water regime. Grain yield was closely associated with traits related to grain numbers. In all three moisture regimes, positive correlations were observed between grain yield and photosynthesis that were dependent on the timing or physiological growth stage of the photosynthetic measurement: highly significant correlations were found in the mid‐ and late grain filling stages, but no correlations at anthesis. Consistent with these findings, flag leaf senescence at the late grain filling stage was negatively correlated with grain yield and photosynthetic rate (under terminal drought and dryland conditions). These findings provided evidence that grain yield was sink‐limited until the final stages of growth, at which time sustained photosynthesis and delayed senescence were critical in filling grain. Because the trends were consistent in moisture sufficient and deficient conditions, the results suggest that late‐season photosynthesis and delayed leaf senescence are driven by the size of the reproductive carbon sink, which was largely governed by factors affecting grain numbers.

Evaluation of Elite Spring Wheat (Triticum aestivum L.) Genotypes for Yield and Yield Attributing Traits under Irrigated Condition

Thirty International Maize and Wheat Improvement Centre (CIMMYT) elite lines and Nepalese commercial wheat varieties were grown at Agriculture and Forestry University, Chitwan in Alpha-lattice design to identify high yielding genotypes, yield attributing parameters and correlations between them. Observations were taken for different morpho-physiological and yield attributing traits i.e., days to booting, heading, anthesis, maturity, flag leaf senescence, flag leaf duration, grain filling duration, plant height, spike length, number of grains per spike, thousand kernel weight, hectoliter weight, grain yield and biomass yield. Significant genotypic differences were observed for all the traits studied indicating considerable amount of variation among genotypes for each character. The mean grain yield was 2148 kg/ha and it ranged from 1000 to 3425 kg/ha. BLOUK#1/4/WHEAR/KUKUNA/3/C80.1/3*BATAVIA//2*WBLL1/5/MUNAL #1 (35th ESWYT138) was the highest grain yielding genotype among all followed by CHIBIA//PRLII/CM65531/3/FISCAL/4/DANPHE#1/5/CHIBIA//PRLII/CM65531/3/SKAUZ/BAV92 (ESWYT 141), Gautam, Vijay and CHYAK1*2/3/HUW234+LR34/PRINIA//PFAU/WEAVER (ESWYT129). Grain yield had significant strong positive correlation with grain filling duration (0.685**), plant height (0.606**), thousand kernel weight (0.675**), biomass yield (0.892**) and hectoliter weight (0.586**). Four clusters were formed by cluster analysis and genotypes were grouped in a particular cluster on the basis of similarity of morpho-physiological traits. So, these genotypes may be exploited for their direct release or as parents in hybridization programmes to develop high yielding wheat varieties.Int. J. Appl. Sci. Biotechnol. Vol 5(2): 194-202

Irrigation methods affect wheat flag leaf senescence and chlorophyll fluorescence in the North China Plain

The water resource shortage in North China Plain is an increasing threat to the sustainabilityof wheat (Triticum aestivum L.) production. A two-year field experiment was conducted toexamine the effects of two supplemental irrigation (SI) methods on wheat flag leaf senescence,chlorophyll fluorescence and grain yield. The following field treatments were conducted:no irrigation (W0); SI with 60 mm of water at jointing and anthesis stages (local quota SI, Wck);SI based on the relative soil water content (SWC) of 0–40 cm soil layers with 65% fieldcapacity (FC) at jointing stage and 70% FC at anthesis stage (W1); SI based on SWC of samesoil layers with 70% FC at the jointing and anthesis stage (W2); and SI based on the SWC ofsame soil layers with 75% FC at jointing stage and 70% FC at anthesis stage (W3). Resultsshowed that W0 accelerated flag leaf senescence and had reduced grain yield. Among irrigationtreatments, W2 (and W3 in 2013-2014) significantly increased flag leaf water potential from7 to 28 days after anthesis (DAA) compared with Wck and W1. Superoxide dismutase activity,catalase activity of W2 increased by 15.41% and 14.96% compared with those in Wck, resultingin the significantly decreased concentration of malondialdehyde and increased concentration ofsoluble protein at 14–28 DAA. The Fv/Fm at 21–28 DAA and the ΦPSII, qP and NPQ at 14–28DAA for W2 (and W3 in 2013–2014) were also significantly higher than those of Wck and W1.Eventually, grain yield, water use efficiency and irrigation benefit of W2 were 8704.54 kg ha-1,20.86 kg ha-1 mm-1 and 31.44 kg ha-1 mm-1, respectively, which were the highest among thoseof all the treatments. These values increased by 5.82%, 9.65% and 6.00%, respectively, relativeto those of Wck. In conclusion, the SI based on 0–40 cm soil layer and use of an appropriaterelative SWC (both 70% FC at the jointing and anthesis stages) can reduce irrigation amount,delay leaf senescence and improve grain yield and water use efficiency.

Senescence-specific change in ROS scavenging enzyme activities and regulation of various SOD isozymes to ROS levels in psf mutant rice leaves

To clarify the interaction between different antioxidant enzymes for monitoring oxidative stress and ROS burst in rice senescent leaves, we investigated the genotype-dependent alteration in temporal patterns of the O2•− production rate, H2O2 content, and ROS–scavenging enzyme activities during leaf senescence in two rice genotypes, namely, the premature senescence of flag leaf (psf) mutant and its wild type. Results showed that the psf mutant differed obviously from its wild type in leaf O2•− generation rate and H2O2 content accumulation, and the decreased activities of SOD, CAT, and APX in the psf leaves were strongly responsible for the increased ROS level and the accelerated leaf senescence. By contrast, the increase in POD activity was positively correlated with the senescence-related enhancement in O2•− generation in rice leaves. Among various SOD isoforms, Mn–SOD responded sensitively to the increasing O2•− generation rate, whereas Cu/Zn–SOD remained stable with the progression of leaf senescence. These findings suggest that the senescence-related decline in total SOD activity was mostly attributable to the downregulation of both the translation and transcription of Mn–SOD isoform. This occurrence finally resulted in the collapse of SOD defense system and accelerated leaf senescence for the psf mutant. Furthermore, we presented the possible contribution of several Cu/Zn–SOD expression patterns to the senescence-related O2•− detoxification in different cell compartments.

Zymoseptoria tritici development induces local senescence in wheat leaves, without affecting their monocarpic senescence under two contrasted nitrogen nutrition

Zymoseptoria tritici causes large losses in wheat yield usually related to the losses of green area. However, the issue of whether green area losses result from the local necrosis or from acceleration in the monocarpic apical senescence remains open.The present study examined whether leaf inoculation with Zymoseptoria tritici modifies apical senescence of flag leaf in wheat cultivar Soissons grown under two contrasted nitrogen nutritions.The dynamics of local and apical senescences and the pycnidia number were measured repeatedly throughout the grain filling. Local and apical senescence were adjusted to functions, the parameters of which were analyzed according to nitrogen and inoculation treatments. The intra-leaf gradient of residual nitrogen concentration was measured at plant maturity.The relative rate of apical senescence increased twofold when fertilization was withheld. Both treatments, inoculation and nitrogen, generated a large range of disease that developed to different extents, resulting from different rates and timing. Local necrosis and pycnidia number strongly varied with nitrogen nutrition but necrosis varied in the same extent as apical senescence, thus green area relative loss was unaffected by nitrogen nutrition. By opposition, apical senescence was never affected at any time by the inoculation. Residual nitrogen increased in the inoculated portions of the infected leaves, in correlation with local necrosis, whereas the residual nitrogen in the non-inoculated part of infected leaves stayed at the level of control leaves.Apical senescence was managed at the leaf tissue level, according to nitrogen availability but regardless of disease, a useful output for modelling.

Relationships between δ13C, δ18O and grain yield in bread wheat genotypes under favourable irrigated and rain-fed conditions

In previous investigations, carbon isotope composition (δ13C) has been used in C3 cereals to screen for genotypes with high transpiration efficiency and oxygen isotope composition (δ18O) has been shown to correlate with transpiration rate. We examined associations of δ13C of the grain and flag leaf and δ18O of the flag leaf with respect to grain yield in wheat cultivars in UK field conditions. Field experiments were carried out at University of Nottingham in 2009–10 and 2010–11 testing 17 wheat cultivars under fully irrigated and rain-fed conditions. Averaging across years grain yield was reduced by 1.69tha−1 (16.5%) in the rain-fed treatment (P<0.001). There was a negative linear relationship between grain yield and grain δ13C amongst cultivars, under both irrigated (R2=0.47, P<0.01) and rain-fed (R2=0.70, P<0.001) conditions. Grain δ13C was negatively correlated with flag-leaf stomatal conductance (r=−0.94, P<0.01) in a subset of six of the cultivars, indicating that higher transpiration efficiency was associated with lower stomatal conductance. The associations between grain yield and flag-leaf δ13C and flag-leaf δ18O amongst cultivars under irrigated and rain-fed conditions were not statistically significant. There was a positive linear relationship between flag-leaf δ18O and grain δ13C amongst cultivars under irrigated conditions (R2=0.38, P<0.01), indicating a trade-off between transpiration and transpiration efficiency (TE). Genetic variation in grain yield under rain-fed conditions was also associated with delayed onset of flag-leaf senescence (R2=0.35, P<0.05). The 17 wheat cultivars ranged in year of release (YoR) from 1964 to 2009 and grain yield increased linearly under irrigated conditions by 60.4kgha−1yr−1 (0.72%yr−1) and under rain-fed conditions by 47.5kgha−1yr−1 (0.66% yr−1) over the 45year period and grain δ13C composition decreased by 0.0255 and 0.0304‰ yr−1, respectively, indicating genetic gains in wheat yield potential in the UK seem likely to have been achieved through a lower TE, higher water uptake and lesser limitation of stomatal conductance.

Evaluation of agronomic traits and spectral reflectance in Pacific Northwest winter wheat under rain-fed and irrigated conditions

The US Pacific Northwest (PNW) is characterized by high latitude and Mediterranean climate where wheat production is predominantly rain-fed and often subject to low soil moisture. As a result, selection for drought-adaptive traits in modern cultivars has been an integral component of the regional breeding programs. The goal of this research was to evaluate phenotypic associations of morpho-physiological traits and their response to soil moisture variation in winter wheat germplasm adapted to the PNW. A panel of 402 winter wheat accessions (87 hard and 315 soft) was evaluated for spectral reflectance indices (SRIs), canopy temperature (CT), plant stature, phenology, grain yield, and yield components under rain-fed and irrigated conditions in 2012–2014. Variation in soil moisture and temperature cumulatively explained 86% of total yield variation across years and locations. The phenotypic associations of yield with phenology, plant height, and CT were environment dependent. Various SRIs related to biomass, stay green, pigment composition, and hydration status showed consistent patterns of response to drought and strong correlations with yield (p<0.001). The compensatory interaction of grain number and weight was indicated in the negative correlation between thousand kernel weight and grain number per spike across moisture regimes. Area under vegetation index curve (AUVIC) explained 53–88% of the total variation in stay green estimated from visual score of flag leaf senescence (p<0.001). Principal component analysis revealed three major clusters that explained more than 76% of interrelations among traits. The market classes within the study population showed differentiation with respect to these traits. This study highlights the potential use of spectral radiometry in field screening of winter wheat for grain yield and drought adaptation in Mediterranean-like environments.

Comparison of photosynthetic decline of flag leaves between two high-yield wheat varieties

Photosynthetic properties were investigated in two newly-developed high-yield wheat (Triticum aesticum L.) varieties, Ningmai 8 and Ningmai 9, in order to elucidate both photosynthetic decline of flag leaf senescence, and variety differences. The results showed that, after anthesis, with increasing ear mass and specific leaf mass, there were decreases in relative water content, chlorophyll content, light-saturated net photosynthetic rate (P nmax ), light saturation point (LSP), apparent quantum yield (AQY), and electron transfer activities of PSI, PSII and whole electron transport chain, especially significant after yellow ripening, whereas ratio of chl a/b, light compensation point (LCP) and respiration rate (R d) were gradually increased from anthesis to yellow ripening, and after that rose markedly. The findings here indicated that before yellow ripening, P nmax decreased slowly with wider range of light availability, and after that P nmax dropped quickly with less range of light availability. Compared with Ningmai 8, Ningmai 9 with higher yield showed earlier senescence in flag leaves.

Leaf photosynthesis and associations with grain yield, biomass and nitrogen-use efficiency in landraces, synthetic-derived lines and cultivars in wheat

Future genetic progress in wheat grain yield will depend on increasing above-ground biomass and this must be achieved without commensurate increases in N fertilizer inputs to minimise environmental impacts. Our objective was to quantify variation in grain yield, above-ground biomass and N-use efficiency (NUE) and associated traits in a panel of diverse hexaploid wheat germplasm comprising: (i) landraces from the AE Watkins collection, (ii) synthetic-derived hexaploid lines in a cv. Paragon spring wheat background and (iii) UK modern cultivars including cv. Paragon under low N and high N conditions. A field experiment was carried out in two seasons examining 15 genotypes (five landraces, five synthetic-derived (SD) hexaploid lines and five UK modern cultivars) under low N and high N conditions at Nottingham University farm, UK. Machine-harvested grain yield, above-ground biomass and NUE were measured. Physiological traits were assessed including flag-leaf light-saturated photosynthetic rate (Amax) and relative chlorophyll content (SPAD) under HN conditions; and flag-leaf senescence duration and rate and Normalized Difference Vegetative Index (NDVI) under LN and HN conditions. Under HN conditions, the modern cultivars overall produced higher grain yield than the SD lines (+9.7%) and the landraces (+60.4%); and the modern cultivars and SD lines also produced higher biomass than the landraces (30.3% and 28.4%, respectively). Under LN conditions, reduction in grain yield and biomass compared to HN conditions was least for the landraces (−1% and −8.6%, respectively), intermediate for the SD lines (−7.4 and −10.2%, respectively) and highest for the modern cultivars (−9.3 and −24.6%, respectively). As a result, the SD lines had higher biomass (+17%) than the modern cultivars under LN conditions. Under HN conditions the synthetic derivatives (23.8μmolm−2s−1) and modern cultivars (241.1μmolm−2s−1) had higher pre-anthesis Amax than the landraces (19.7μmolm−2s−1) (P<0.001). Pre-anthesis Amax was strongly positively linearly associated with above-ground biomass (R2=0.63, P<0.001) and grain yield (R2=0.75, P<0.001) amongst the 15 genotypes. Flag-leaf Amax was also positively linearly associated with flag-leaf relative chlorophyll content at anthesis (R2=0.74; P<0.001). Comparing the SD lines to the recurrent parent Paragon, under HN conditions one line (SD 22) had higher pre-anthesis flag-leaf Amax than Paragon (P<0.05). Under LN conditions one line (SD 24, +27%) had higher yield than Paragon (P<0.05) and two lines (SD 24 and SD 38, +32% and +31%, respectively) had more biomass than Paragon (P<0.05). Our results indicated that introgressing traits from synthetic-derived wheat and landraces into UK modern wheat germplasm offers scope to raise above-ground biomass and grain yield in moderate-to-low N availability environments.