Post-anthesis Water Deficit Research Articles

Wheat Water-Soluble Carbohydrate Remobilisation under Water Deficit by 1-FEH w3.

Fructan 1-exohydrolase (1-FEH) is one of the major enzymes in water-soluble carbohydrate (WSC) remobilisation for grains in wheat. We investigated the functional role of 1-FEH w1, w2, and w3 isoforms in WSC remobilisation under post-anthesis water deficit using mutation lines derived from the Australian wheat variety Chara. F1 seeds, developed by backcrossing the 1-FEH w1, w2, and w3 mutation lines with Chara, were genotyped using the Infinium 90K SNP iSelect platform to characterise the mutated region. Putative deletions were identified in FEH mutation lines encompassing the FEH genomic regions. Mapping analysis demonstrated that mutations affected significantly longer regions than the target FEH gene regions. Functional roles of the non-target genes were carried out utilising bioinformatics and confirmed that the non-target genes were unlikely to confound the effects considered to be due to the influence of 1-FEH gene functions. Glasshouse experiments revealed that the 1-FEH w3 mutation line had a slower degradation and remobilisation of fructans than the 1-FEH w2 and w1 mutation lines and Chara, which reduced grain filling and grain yield. Thus, 1-FEH w3 plays a vital role in reducing yield loss under drought. This insight into the distinct role of the 1-FEH isoforms provides new gene targets for water-deficit-tolerant wheat breeding.

Interaction of iron and zinc fortification and late-season water deficit on yield and fatty acid composition of Dragon's Head (Lallemantia iberica L.)

Dragon's head (Lallemantia iberica) is a rich source of alpha-linolenic acid, linoleic acid, essential oil, protein, and mucilage. Therefore, the aim of this study was to evaluate the effects of foliar application of three different concentrations of Fe and Zn (control, 4, and 8 g lit−1) at two different developmental stages (vegetative stage (VS) and reproductive stage (RS)) on the quantity and quality of dragon's head seed yield and fatty acid composition in two crop seasons (2018 and 2019) under two environments (normal irrigation as control (NI) and post-anthesis water deficit (WD). In NI, average yields of seed, oil, and protein were 1155, 340, and 183 kg ha−1, respectively, and in the WD, they were 879, 283, and 148 kg ha−1, respectively. By applying Zn and Fe, the mean values of seed, oil, and protein yields in the NI were 1425, 478, and 264 kg ha−1, while in the WD, they were 1011, 354, and 200 kg ha−1, respectively. Furthermore, the application of WD resulted in a significant increase in zinc concentration, protein percentage, and saturated fatty acid percentage in seeds. Unlike WD, iron and zinc treatments decreased the percentage of saturated fatty acids and increased the percentage of unsaturated fatty acids. The number of capsules per plant had the most positive indirect effect on grain yield. The results showed that foliar spraying of Fe and Zn could effectively mitigate the adverse effects of WD on the quality and quantity of seed and oil yield dragon's head.

Kernel Water Relations and Kernel Filling Traits in Maize (Zea mays L.) Are Influenced by Water-Deficit Condition in a Tropical Environment.

Water deficit is a major limiting condition for adaptation of maize in tropical environments. The aims of the current observations were to evaluate the kernel water relations for determining kernel developmental progress, rate, and duration of kernel filling, stem reserve mobilization in maize. In addition, canopy temperature, cell membrane stability, and anatomical adaptation under prolonged periods of pre- and post-anthesis water deficit in different hybrids was quantified to support observations related to kernel filling dynamics. In this context, two field experiments in two consecutive years were conducted with five levels of water regimes: control (D1), and four water deficit treatments [V10 to V13 (D2); V13 to V17 (D3); V17 to blister stage (D4); blisters to physiological maturity (D5)], on three maize hybrids (Pioneer 30B80, NK 40, and Suwan 4452) in Expt. 1. Expt. 2 had four water regimes: control (D1), three water deficit treatments [V10 to anthesis (D2); anthesis to milk stage (D3); milk to physiological maturity (D4)], and two maize hybrids (NK 40 and Suwan 4452). Water deficit imposed at different stages significantly reduced maximum kernel water content (MKWC), kernel filling duration (KFD), final kernel weight (FKW), and kernel weight ear–1 while it increased kernel water loss rate (KWLR), kernel filling rate (KFR), and stem weight depletion (SWD) across maize hybrids in both experiments. The lowest MKWC under water deficit was at D3 in both experiments, indicating that lower KFR results in lowest FKW in maize. Findings indicate that the MKWC (R2 = 0.85 and 0.41) and KFR (R2 = 0.62 and 0.37) were positively related to FKW in Expt. 1 and 2, respectively. The KFD was reduced by 5, 7, 7, and 11 days under water deficit at D3, D4 in Expt. 2 and D4, D5 in Expt. 1 as compared to control, respectively. Water deficit at D5 in Expt. 1 and D4 in Expt. 2 increased KWLR, KFR, and SWD. In Expt. 2, lower canopy temperature and electrical conductivity indicated cell membrane stability across water regimes in NK 40. Hybrid NK 40 under water deficit had significantly higher cellular adaptation by increasing the number of xylem vessel while reducing vessel diameter in leaf mid-rib and attached leaf blade. These physiological adjustments improved efficient transport of water from root to the shoot, which in addition to higher kernel water content, MKWC, KFD, KFR, and stem reserve mobilization capacity, rendered NK 40 to be better adapted to water-deficit conditions under tropical environments.

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.

Responses of Six Oil Sunflower (Helianthus annuus L) Genotypes to Post-Anthesis Water Deficit

A field experiment was carried out to evaluate the responses of six oil sunflower (Helianthus annuus L) genotypes namely; Sakha 53, H(A9XRf6), B11, B12, H(A9XRf8) and B20 to drought stress. Plants were subjected to three levels of water: adequate (control), moderate drought and severe drought Water regime was started directly post anthesis by withholding water during seed-filling stage until complete maturity of seeds. Moderate and severe drought decreased plant height and stem diameter of all genotypes, except B11 and B20 which recorded non-significant decrease in plant height under moderate drought. On the other hand, non-significant effect was observed in leaf area in all genotypes except B12 and H(A9XRf8) where a significant decrease was recorded only under severe drought. Yield components (head diameter, seed yield, 100 seed weight, seed husk %, seed kernel %, and oil percentage) responded to drought stress differently according to genotypes. Significant decreases were observed in floral head diameter seed yield, oil percentage and protein content in all genotypes except for the non-significant reduction in seed yield and oil content in Sakha53 and H(A9XRf6) under moderate drought Generally, Skha53 was the most drought-tolerant genotype whereas B11, B12 and B20 exhibited the least tolerance.

Analyse Genotypique De La Contribution De La Matiere Assimilée Du Pedoncule Dans Le Remplissage Du Grain Chez Le Ble Dur (Triticum Durum D.E.S.F.)

In a part of study on morpho-physiological characterization in durum wheat; we were interested in quantifying the stem dry matter produced after anthesis and its contribution in the grain filling. When the climatic conditions are unfavorable ; the photosynthetic activity of the post-anthesis is reduced. The plant then uses the assimilates stored in the stem to increase its filling rate of grain. Thus, the behavior of four varieties of durum wheat is analyzed in the field using different parameters: (i) relative water content (RWC) of the flag leaf (ii) dry weight development of the grains (iii) peduncle assimilated dry matter contribution in the grain filling. The leaf water status, appreciated by measuring the RWC, is an indicator of the photosynthetic apparatus functioning. The measured values showed a significant difference between two agricultural companions. The results also showed a genotypic difference in the dry matter accumulation in the grains, mainly related to its filling speed. The accumulation of assimilates in the peduncle during the days following flowering, constitutes an advantage of reserves in dry matter before installation of water deficit. Indeed, it affects production by decreasing the photosynthetic activity. In conclusion, this experiment has highlighted two types of grain yield elaboration of cultivated wheat in the post-anthesis water deficit conditions.

Effect of nitrogen fertiliser management on soil mineral nitrogen, nitrous oxide losses, yield and nitrogen uptake of wheat growing in waterlogging-prone soils of south-eastern Australia

Some of the highest nitrous oxide (N2O) emissions arising from Australian agriculture have been recorded in the high-rainfall zone (>650mm) of south-western Victoria. Understanding the association between nitrogen (N) management, crop N uptake and gaseous losses is needed to reduce N2O losses. Field experiments studied the effect of N-fertiliser management on N2O emissions, crop N uptake and crop productivity at Hamilton and Tarrington in south-western Victoria. Management included five rates of urea-N fertiliser (0, 25, 50, 100 and 200kgN/ha) topdressed at either mid-tillering or first-node growth stages of wheat development; urea-N deep-banded 10cm below the seed at sowing; and urea coated with the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) was either topdressed or deep-banded. Pre-sowing soil profile chemical properties were determined before static chambers were installed to measure N2O losses, accompanied by wheat dry matter, crop N uptake and grain yield and quality, to measure treatment differences. N2O losses increased significantly (P≤0.10) where urea-N was deep-banded, resulting in a 2–2.5-fold increase in losses, compared with the nil N control. The high N2O losses from deep-banding N appeared to result from winter waterlogging triggering gaseous or drainage losses before wheat reached peak growth and demand for N in spring. Despite the high losses from deep-banding urea-N, grain yields were largely unaffected by N management, except at Hamilton in 2012, where topdressed wheat growing in a soil with large reserves of NO3–-N, and later experiencing post-anthesis water deficit resulted in a negative grain yield response. All sites had high concentrations of soil organic carbon (>2.8%) and the potential for large amounts of N mineralisation throughout the growing season to supplement low N fertiliser recovery. However, topdressed urea-N resulted in significant enrichment of crop tissue (P≤0.004) and associated positive response in grain protein compared with the deep banded and nil N treatments. 3,4-Dimethylpyrazole phosphate (DMPP)-coated urea provided no additional benefit to crop yield over conventional urea N. Our study highlighted the importance of synchronising N supply with peak crop N demand to encourage greater synthetic N uptake and mitigation of N2O losses.

Variation in leaf photosynthetic response of rice genotypes to post-anthesis water deficit

Variation in the response of six diverse rice genotypes to imposed water stress was investigated in terms of leaf photosynthetic traits and leaf water potential measurements (Ψleaf) during and following a period of water stress. The Ψleaf reduced from 0 days up to 6th day of irrigation deprivation and the reduction in Ψleaf was more pronounced in Swarna and minimum in PA-6201. A gradual recovery in Ψleaf was observed in all the tested varieties after re-irrigation. Similarly, water stress significantly reduced rate of photosynthesis (P N), stomatal conductance (g s), transpiration (E) and internal CO2 concentration (C i). Significant differences were noticed amongst the varieties in their response to water stress. The P N partially recovered in all tested varieties after re-irrigation. Vandana recorded greater recovery (65 %), where as the recovery was only 32 % in Sugandha Samba. Water stress (6 days of irrigation deprivation) significantly decreased the mean Chl a, Chlb, total chlorophyll and total carotenoid content. However, a marginal increase in total chlorophyll was observed under water stress in Vandana and N-22. Water stress had no significant effect on maximum photochemical efficiency (F v/F m) for all the tested varieties. However, in Sugandha Samba and Swarna a significant reduction was noticed. Water stress reduced the efficiency of excitation capture (Φe), in vivo quantum yield of PSII photochemistry (ΦPSI), coefficient of photochemical quenching (qP) and increased the coefficient of non-photochemical quenching (qN). The data on photosynthetic traits and chlorophyll fluorescence parameters indicate that Vandana, N-22, DRR-Dhan-38 and PA-6201 which maintained relatively higher, Ψleaf, P N and g s under water stress and could also maintain high values of photochemical efficiency (Fv/Fm, Φe, ΦPSI and ETR) than Sugandha Samba and Swarna and the genotypic differences in the response of PSII activity could be exploited as traits for the selection of drought tolerant rice genotypes.

Effect of post-anthesis water deficit on yield and some physiological parameters on two wheat cultivars

This work investigates the effects of water deficit on physiologic parameters related to yield in two wheat cultivars (Triticum aestivum L.), Marvdasht and Zagros (sensitive and tolerant to terminal season drought, respectively) grown in pots under well watered and water-stressed starting from anthesis until maturity. All physiological parameters were affected by drought stress. Results showed that, water deficits enhanced the senescence by accelerating loss of leaf chlorophyll and soluble proteins and the loss was more in Marvdasht than Zagros. The net CO2 assimilation rate (PN) in flag leaves during water deficit display a strict correlation with the drought sensitivity of the genotypes and showed an early reduction in Marvdasht. Water stress resulted in a marked increase in leaf proline content of the drought-tolerant that led to alleviate the deleterious effect of water stress whereas, a slightly increment at the end of grain development observed in drought sensitive cv. The effect of drought on grain yield was primarily due to the significant reduction in grain weight, particularly in drought-sensitive. The results indicate that grain filling processes under water restriction are limited by low substrate availability and reduced synthesis capacity of the sink. These results raise the possibility that water stress-induced elevated levels of proline in Zagros contribute to reduce harmful of stress during grain filling. Key words: Chlorophyll, flag leaves, grain yield, proline, soluble proteins, wheat (Triticum aestivum L.).

Relationship of Endogenous ABA and IAA to Accumulation of Grain Protein and Starch in Two Winter Wheat Cultivars under Post-anthesis Water Deficit

Accumulation of protein and starch in grain is a key process determining grain yield and quality in wheat. Under drought endogenous plant hormone levels will change and may have an impact on the yield and quality of wheat. In a greenhouse experiment, two winter wheat (Triticum aestivum L.) varieties differing in post anthesis drought resistance, tolerant (cv. Zagros) and sensitive (cv. Marvdasht), were subjected to either well-watered (WW) or water-stressed (WS) from anthesis to maturity. On the 7, 15 (grain enlargement stage) and 31 (grain filling stage) days after anthesis (DAA), endogenous abscisic acid (ABA) and indole-3-acetic acid (IAA) were determined in grain of wheat plants by enzyme linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in two varieties. The ABA levels were much higher under water deficit than well water treatment. In comparison grain ABA levels in all sampling stages was more in Marvdasht than Zagros. The endogenous grains IAA content display a marked reduction by the time and the water stress aggravated this reduction in both cultivars, however, the depresstion was more in drought-sensitive than drought-tolerant. The relationship between yields and contents of starch and protein in grains and levels of two hormones in sink organ indicated that the changes in yield and content of grain starch and protein under water withholding were associated with the reduced IAA and elevated ABA level in grains. It was proposed that the changed levels of endogenous hormones under drought post-anthesis might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzymes and processes.

Evaluation of a reduced-tillering (tin) gene in wheat lines grown across different production environments

Post-anthesis water deficit and increasing vapour pressure deficit are common and can result in reduced grain yield and the development of small or shrivelled wheat kernels (screenings) that reduce grain value. Previous studies suggest incorporation of a tiller inhibition (tin) gene to restrict tiller number and thereby slow water use and promote the development of larger, fertile spikes to increase kernel weight. This paper reports on the influence of the tin gene on grain yield and screenings in multiple wheat genetic backgrounds assessed in field experiments in 2005 and 2006. Across environments, grain yield ranged from 0.90 to 5.50 t/ha and screenings from 4 to 20%. The effect of tin on grain yield and screenings varied with environment and genetic background. Grain yield was unchanged in tin lines derived from varieties Brookton, Chara, and Wyalkatchem assessed in southern Australian environments. However, there was a 31 and 10% advantage of free-tillering over tin-containing Silverstar lines for the 2005 western and 2006 northern experiments, respectively, resulting in an average 12% reduction in grain yield of Silverstar tin lines. In northern experiments, where screenings ranged from 4 to 12%, Silverstar-based tin lines produced significantly fewer screenings than free-tillering sister lines. Reduction in screenings was associated with a higher kernel weight (+10%) and a tendency for lower grain yield, although individual Silverstar tin progeny with grain yield equivalent to the parent were readily identified. The incorporation of the tin gene has considerable potential to reduce the incidence of screenings in commercial wheat crops. Variation in grain yield associated with the tin gene was dependent on genetic background, with potential for selection of higher yielding tin progeny for commercial line development.

Remobilization of dry matter in wheat: effects of nitrogen application and post-anthesis water deficit during grain filling

Pre-anthesis stored dry matter in wheat (Triticum aestivum L.) is important in a Mediterranean climate because grain filling greatly depends on the remobilization of pre-anthesis assimilates. A water deficit at the post-anthesis stage may increase the dry matter stored before anthesis. This field study assessed the effects of post-anthesis water deficit and the application of nitrogen (N) fertilizer on three wheat cultivars. Data collected over 2 years showed that, in wheat with a post-anthesis water deficit (WD), dry matter remobilization efficiency reached its maximum (29%) at 80 kg N ha−1, but further additions of N decreased it. The contribution of remobilized dry matter to a grain ranged from 7% to 23% of the grain's dry weight and, in WD grain, was 78% more than that of well-watered (WW) grain. Grain from plots on which fertilizer had been applied had a lower proportion of remobilized dry matter than did grain from unfertilized plots. For grain from adequately fertilized treatments, limited irrigation was associated with reduced dry matter remobilization. The amount of non-structural carbohydrates (NSC) remaining in parts of the plant was much greater in the WW than in the WD treatments. The 160 kg N ha−1 treatment also left more NSC unused than did the no N treatment. The active grain-filling period was shortened substantially by a water deficit, but this was countered by the application of 160 kg N ha−1. Grain-filling rates for all cultivars or all N treatments were increased by inducing a water deficit. For WD grains, kernel weight was reduced when fertilizer application rates were 0–80 kg N ha−1, but increased when rates were 160 kg N ha−1, unlike WW grain exposed to similar fertilizer regimes. The grain yield of WD wheat was reduced by 25%, and that of grain receiving no fertilizer was 15% lower than that receiving 80 kg N ha−1. Among three wheat cultivars, cv. Chamran produced the highest grain yield (19% higher than that of either cv. Shiraz or cv. Marvdasht). It was concluded that the stored carbohydrate had provided an important buffer against water stress during grain filling, in terms of yield.

English

Pre-anthesis stored nitrogen in wheat (Triticum aestivum L.) is important because grain filling greatly depends on the remobilization of pre-anthesis nitrogen under Mediterranean growth conditions. This field study was conducted to assess the effect of post-anthesis water deficit and three N fertilizer levels on N remobilization and N losses in three wheat cultivars (‘Shiraz’, ‘Marvdasht’ and ‘Chamran’). Nitrogen remobilization in plant parts decreased to 29 to 58% under water deficit compared with the well watered (WW) treatment. Grain N was 40% higher under post-anthesis water deficit than the WW treatment and with the addition of 160 kg N ha-1. The application of nitrogen fertilizer increased N remobilization to 78%. ‘Shiraz’ remobilized 13 and 25% more nitrogen than ‘Marvdasht’ and ‘Chamran’, respectively. Under water deficit, N remobilization efficiency increased by 13%. Leaves were more efficient than stem and spike in N remobilization efficiency either in the WW or the WD treatment. The application of fertilizer N generally lowered whole plant remobilization efficiency. The N remobilization efficiency of ‘Chamran’ increased when the soil moisture and/or N were limited during the grain filling period. Grain N concentration was correlated positively with N concentration or N content of vegetative parts at anthesis. In addition to nitrogen fertilizer, WD during grain filling reduced nitrogen use efficiency by 30 and 25%, respectively. In the WW treatment, 25% of the N at anthesis was lost at maturity. In contrast, under WD only 6% of the N was lost. High amount of N led to N losses at maturity. Significant negative correlations were found between grain yield and grain protein concentration in the three wheat cultivars. Results indicate that the greater the amount of N accumulated before anthesis, the higher the translocation rates of nitrogen to grain and the greater the risk of net N losses at maturity. Key words: Nitrogen harvest index, nitrogen loss, grain protein, nitrogen use efficiency.

Response of Different Bread Wheat (Triticum aestivum L.) Genotypes to Post-Anthesis Water Deficit

Resources of water are limited in many agricultural areas of West Asia. Therefore, effective use of this scarce resource is very important in this region. So, this research was conducted in 2009-2010 growing season at Research Farm of Agricultural Researches Center of Khuzestan, Iran, to investigate the effects of two irrigation regime (I 1 : normal irrigation and I 2 : no irrigation in post-anthesis growth stage) on grain yield of five wheat cultivars (‘Chamran’, ‘S-78-11’, ‘A’and ‘S-82-10’). A split plot experiment based on randomized complete block design in three replications was used, with the irrigation regime in main plots and wheat cultivars in subplots. The results showed that 1000-grain weight, grains per spikelet and grain yield were decreased by water limitation. Despite of their significant differences (P<0.05) in 1000-grain weight, spikelets per spike and grains per spike, the grain yield of wheat cultivars was not significantly different. It was resulted by different grain yield reduction of genotypes under different irrigation regimes. Genotypes ‘S-80-18’ and ‘S-7811’ produced highest yield under normal irrigation and drought stress conditions, respectively. The yield reduction of ‘S-80-18’ genotype was highest under drought stress conditions. ‘S-78-11’ was the most tolerant genotype to water deficit occurrence.

Sorghum stay-green QTL individually reduce post-flowering drought-induced leaf senescence

Sorghum is an important source of food, feed, and biofuel, especially in the semi-arid tropics because this cereal is well adapted to harsh, drought-prone environments. Post-flowering drought adaptation in sorghum is associated with the stay-green phenotype. Alleles that contribute to this complex trait have been mapped to four major QTL, Stg1-Stg4, using a population derived from BTx642 and RTx7000. Near-isogenic RTx7000 lines containing BTx642 DNA spanning one or more of the four stay-green QTL were constructed. The size and location of BTx642 DNA regions in each RTx7000 NIL were analysed using 62 DNA markers spanning the four stay-green QTL. RTx7000 NILs were identified that contained BTx642 DNA completely or partially spanning Stg1, Stg2, Stg3, or Stg4. NILs were also identified that contained sub-portions of each QTL and various combinations of the four major stay-green QTL. Physiological analysis of four RTx7000 NILs containing only Stg1, Stg2, Stg3, or Stg4 showed that BTx642 alleles in each of these loci could contribute to the stay-green phenotype. RTx7000 NILs containing BTx642 DNA corresponding to Stg2 retained more green leaf area at maturity under terminal drought conditions than RTx7000 or the other RTx7000 NILs. Under post-anthesis water deficit, a trend for delayed onset of leaf senescence compared with RTx7000 was also exhibited by the Stg2, Stg3, and Stg4 NILs, while significantly lower rates of leaf senescence in relation to RTx7000 were displayed by all of the Stg NILs to varying degrees, but particularly by the Stg2 NIL. Greener leaves at anthesis relative to RTx7000, indicated by higher SPAD values, were exhibited by the Stg1 and Stg4 NILs. The RTx7000 NILs created in this study provide the starting point for in-depth analysis of stay-green physiology, interaction among stay-green QTL and map-based cloning of the genes that underlie this trait.

Transport of dry matter into developing wheat kernels and its contribution to grain yield under post-anthesis water deficit and elevated temperature

Two experiments were conducted on stress-tolerant Suneca and stress-susceptible Batavia wheat varieties which were grown in pots in a temperature-controlled naturally illuminated glasshouse (March–May) under 25/18 °C day/night cycle. Plants were divided into two groups at 8 days after anthesis (DAA). Plants of one group were subjected to four water deficit cycles, while the others were irrigated daily as before. Both groups were sub-divided: one was exposed to a higher temperature (30/25 °C day/night cycle) for 3 days toward the end of the first drought cycle, and the second was maintained at previous conditions. Plants of the first experiment (excluding high temperature exposed Batavia plant) were arranged in three groups: defoliated, decapitated and intact. Dry weights of leaves, stems, ears and kernels were determined at 6–7 days intervals. A mechanistic model was used to analyze the daily rates of dry matter transport from vegetative organs to kernels, and its contribution to kernel weight. Water deficit did not affect kernel number, while high temperature reduced it significantly. The rate of dry matter accumulation by kernels was considerably decreased by water deficit in both cultivars. High temperatures also reduced the rate of dry matter accumulation in Suneca kernels, but to a lesser extend than water deficit. Dry weight of the intact plants’ vegetative organs (stems plus leaves) decreased during grain filling, probably due to export of non-structural carbohydrates to the developing kernels. By contrast, in decapitated plants, dry weight of the vegetative organs increased during the same period. Rates of transport (probably of non-structural carbohydrates) from vegetative organs to kernels were much higher in Suneca than in Batavia during drought. High temperature reduced this rate in Suneca. Initially, the relative contribution of stem and leaf dry matter to kernels was only 40% of their total dry weight increase in unstressed Suneca plants, indicating that the ear was active. This increased gradually up to 1.00 at 26–27 DAA. The relative contribution of Batavia vegetative organs increased from 0.30 to 0.60. In general, water deficit and high temperature increased the relative contribution of transported dry matter to kernels. The second experiments showed that thousand-kernel weight (TKW) and weight of kernels per ear were more severely decreased by water deficit than by heat in both varieties, and more by water stress in Batavia than in Suneca. Plant exposure to high temperatures reduced the response of TKW to water deficit in both varieties.

Carbon Remobilization and Grain Filling in Japonica/Indica Hybrid Rice Subjected to Postanthesis Water Deficits

Poor grain filling, as in unfilled grains, and unused carbohydrate in straws are two major problems in japonica/indica (J/I) hybrid rice (Oryza sativa L.). This study investigated if an early senescence, induced by controlled postanthesis soil drying, could enhance the remobilization of reserved C to the grains, and therefore improve the grain filling. Two J/I hybrids and one indica/indica (I/I) hybrid were field‐grown. Three levels of soil water potential (ψsoil)—well watered (ψsoil = 0), moderate water deficit (ψsoil = −0.025 MPa), and severe water deficit (ψsoil = −0.05 MPa)—were imposed 9 d after anthesis to maturity. As a result of water deficit treatment, chlorophyll concentrations and photosynthetic rates of flag leaves declined more quickly, indicating an enhanced senescence. The remobilized C reserve from the culm and sheath during grain filling was increased by 47 to 61% for the J/I hybrids and 12 to 26% for the I/I hybrid. Partitioning of 14C from the flag leaves to the grains was increased by 18 to 28%. Active grain‐filling period was shortened by 2.7 to 8.7 d, and grain‐filling rate increased by 0.14 to 0.36 mg d−1 grain−1. Water deficits reduced the grain yield of the I/I hybrid by 2.9 to 16.4% but increased that of the two J/I hybrids by 4.4 to 13.3%. We conclude that if water deficit is properly controlled for J/I, the gain from enhanced remobilization of stored C may outweigh the loss due to shortened photosynthetic duration, leading to a fast grain filling and high grain yield in cases where senescence is unfavorably delayed.

Carbon Remobilization and Grain Filling in Japonica/Indica Hybrid Rice Subjected to Postanthesis Water Deficits

Continued genetic improvement in the ability of hybrid corn (Zea mays L.) to withstand high plant density stress requires agronomists to periodically reassess optimal plant density and row width. Furthermore, the optimal plant density level and row width for corn grain yield may vary with location, primarily latitude, in the Corn Belt. This study was conducted to evaluate corn grain yield, harvest moisture, test weight, and stalk lodging with modern corn hybrids, as affected by row width and plant density in the northern Corn Belt. At six locations in 1998 and 1999, four hybrids differing in relative maturity, ear type, plant height, and leaf orientation were planted at row widths of 76, 56, and 38 cm and five plant density levels ranging from 56000 to 90000 plants ha−1. Plots were arranged randomly in a split-split plot configuration. Results show that corn grain yield increased 2 and 4% and harvest moisture decreased by a factor of 2.1% when row width was narrowed from 76 cm to 56 cm and 38 cm, respectively. The highest plant density evaluated, 90000 plants ha−1, had the highest grain yield. Grain moisture decreased and grain test weight increases slightly as plant density increased. A hybrid × row width interaction was not observed indicating that hybrids that yield well in conventional 76-cm row systems will also yield well in narrow row systems.

'Haying-off', the negative grain yield response of dryland wheat to nitrogen fertiliser III. The influence of water deficit and heat shock

Post-anthesis drought and heat shock have been implicated in previous studies as factors contributing to ‘haying-off’ in wheat, but their relative importance has not been investigated. To separate the effects, wheat plants were grown at 2 levels of nitrogen (N) and then exposed to different levels of post-anthesis water deficit in factorial combination with the presence or absence of heat shock. The growth, yield, leaf carbon exchange, water use, and the contents of protein and soluble carbohydrate were measured and compared with the field results reported in Papers I and II of this series. The experiment consisted of wheat plants (cv. Janz) grown in 1·2-m-long tubes outdoors through winter and spring in Canberra, with either nil or 240 kg N/ha applied. The tubes were supported in a refrigerated box to maintain temperatures representative of those of soil in the field, and arranged to form mini-canopies with a density of 29 plants/m2. After anthesis, half of the plants at both levels of N were watered according to their transpiration demand and the other half at 75% of demand to reduce gradually the store of soil water so that water deficit could be initiated at the same time as heat shock. Fifteen days after anthesis, different temperatures were imposed by moving half of the plants into an adjacent glasshouse where heat shock was imposed by raising the air temperature to maxima of ~35ºC for 3 days, to simulate the pattern of temperatures experienced in the field during a heat wave. During this time, the control plants experienced daily maxima of ~25ºC. Following the heat shock, all plants were placed outside and rewatered to enable the assessment of treatment effects on potential leaf function. Both water deficit and high temperature reduced assimilation. After these measurements were taken, well-watered control plants were irrigated according to transpiration demand and the plants with imposed water deficit were watered at 50% of this amount. Yields increased in response to N at both levels of water status and both levels of temperature. That is, there was no evidence of the haying-off reported in Papers I and II of this series. Two factors are proposed to account for the difference between the field crops and the plants grown in the mini-canopy here. Firstly, the pattern of soil-water use differed from the field studies reported in Paper I, with the high-N plants using more soil water than low-N plants during grain filling. Secondly, the level of water-soluble carbohydrates (WSC) in the tube-grown plants of high-N status was greater than that for plants of low-N status, which was opposite to the pattern for field-grown plants reported in Paper II. In addition, the concentrations of WSC in the tube-grown plants were higher than those in the field-grown plants, apparently because lower spike density allowed better penetration of light into the mini-canopies and led to greater assimilate storage than by the denser field crops. The results confirm the conclusion of Paper I that high temperature is not necessary for haying-off, although it is likely that it would worsen the haying-off caused by post-anthesis drought and low WSC reserves in the field. The absence of the haying-off response in this experiment was mostly because the supply of WSC from the sparse canopy was adequate to ofiset the reduction of assimilation due to water deficit and heat shock. A contributing factor to haying-off in the field may therefore be dense canopies resulting in low levels of WSC

Resposta do sorgo granífero a déficits hídricos aplicados durante o ciclo de desenvolvimento da cultura

Os objetivos deste experimento foram analisar os efeitos de déficits hídricos aplicados durante o ciclo de desenvolvimento da cultura do sorgo granífero sobre o dossel vegetativo, senescência das folhas, número e comprimento final de entre-nós. O experimento foi conduzido em um conjunto de lisímetros de drenagem protegidos das precipitações por uma cobertura móvel de plástico transparente. A cultivar Agroceres 3001 foi submetida a quatro tratamentos: bem irrigado, déficit hídrico terminal, déficit hídrico durante o crescimento vegetativo e déficit hídrico após a antese, em três repetições. Os resultados indicaram que o dossel vegetativo das plantas de sorgo foi reduzida quando a fração de água disponível às plantas for inferior a 0,60. O comprimento final dos entre-nós das plantas foi reduzido para déficits hídricos aplicados a partir e durante a fase de crescimento vegetativo. A senescência das plantas de sorgo foi ativada quando a fração de água disponível às plantas foi inferior a 0,50 na profundidade do solo explorado pelo sistema radicular das plantas.