Enhancement of 2-acetyl-1-pyrroline (2AP) concentration,total yield,and quality in fragrant rice through exogenous γ-aminobutyric acid (GABA) application

The effects of exogenous application of γ-aminobutyric acid (GABA) on yield and quality characteristics, especially 2-acetyl-1-pyrroline (2AP) biosynthesis, are rarely investigated. Two field experiments, i.e., experiment 1 (EXP.1) and experiment 2 (EXP.2), were conducted, and four GABA levels, i.e., 0, 50, 500, 1000 mg l⁻¹, classified as CK, T1, T2, and T3, respectively, were sprayed at the initial heading stage of a fragrant rice cultivar, Yuxiangyouzhan. The results showed that exogenous GABA application increased the 2AP content in grains 8.58%–19.44% in EXP.1 and 0.01%–6.22% in EXP.2. Exogenous GABA treatments also increased the GABA concentration in the grains and proline content in fragrant rice. Significant correlations between the grain 2AP content and proline content in leaves at 5 days after spraying were also detected in EXP.1, whereas GABA application did not significantly affect leaf dry weight, total dry weight, or grain yield. Moreover, gas exchange parameters, soil-plant analyses development values, and antioxidant activities were improved under GABA treatments. Additionally, the GABA applications substantially improved the grain quality characteristics, including milled rice percentage, head rice percentage, and protein content. Overall, exogenous GABA application was effective in the improvement of quality characteristics in fragrant rice, especially that of grain 2AP contents.     

Maximizing yields in rice–groundnut cropping sequence through integrated nutrient management

Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted to study the effects of application of green manures [sesbania (Sesbania aculeate Poiret) and crotalaria (Crotalaria juncea L.)] and farmyard manure on productivity of rice (Oryza sativa L.) and its residual effects on subsequent groundnut (Arachis hypogaea L.) crop. Rice and groundnut crops were grown in sequence during rainy and post-rainy seasons with and without green manure in combination with different fertilizer and spacing treatments under irrigated conditions. The results showed that application of green manures sesbania and crotalaria at 10 t ha⁻¹ to rice compared to no green manure application significantly increased grain yield of rice by 1.6 and 1.1 t ha⁻¹, and pod yields of groundnut crop succeeding rice by 0.25 and 0.16 t ha⁻¹, respectively. There was no significant difference between the application of crotalaria or farmyard manure at 10 t ha⁻¹ on grain yields of rice, but pod yields of subsequent groundnut crop were greater with application of green manure. There was no significant effect of different spacing 20×15,15×15,15×10 cm² (333 000; 444 000; 666 000 plant ha⁻¹, respectively) on grain yield of rice. Pod yields of groundnut were significantly greater with closer spacing 15×15 cm² (444 000 plants ha⁻¹) as compared to spacing of 30×10 cm² (333 000 plants ha⁻¹). Maximum grain of rice was obtained by application of 120:26:37 kg NPK ha⁻¹ in combination with green manures, whereas maximum pod yield of groundnut was obtained by residual effect of green manure applied to rice and application of 30:26:33 kg NPK ha⁻¹ in combination with gypsum applied to groundnut crop.     

Long-term effects of inorganic and organic fertilizer sources on yield and nutrient accumulation of lowland rice

Deceleration in rice (Oryza sativa L.) yield over time under fixed management conditions is a concern for countries like Bangladesh, where rice is the primary source of calories for the human population. Field experiments were conducted from 1990 to 1999 on a Chhiata clay loam soil (Hyperthermic Vertic Endoaquept) in Bangladesh, to determine the effect of different doses of chemical fertilizers alone or in combination with cow dung (CD) and rice husk ash (ash) on yield of lowland rice. Two rice crops—dry season rice (December–May) and wet season rice (July–November) were grown in each year. Six treatments—absolute control (T₁), one-third of recommended fertilizer doses (T₂), two-thirds of recommended fertilizer doses (T₃), full doses of recommended fertilizers (T₄), T₂+5 t CD and 2.5 t ash ha⁻¹ (T₅) and T₃+5 t CD and 2.5 t ash ha⁻¹ (T₆) were compared. The CD and ash were applied on dry season rice only. The 10-year mean grain yield of rice with T₁ was 5.33 t ha⁻¹ per year, while the yield with T₂ was 6.86 t ha⁻¹ per year. Increased fertilizer doses with T₃ increased the grain yield to 8.07 t ha⁻¹ per year, while the application of recommended chemical fertilizer doses (T₄) gave 8.87 t ha⁻¹ per year. The application of CD and ash (T₅ and T₆) increased rice yield by about 1 t ha⁻¹ per year over that obtained with chemical fertilizer alone (T₂ and T₃, respectively). Over 10 years, the grain yield trend with the control plots was negative, but not significantly, both in the dry and wet seasons. Under T₃ through T₆, the yield trend was significantly positive in the dry season, but no significant trend was observed in the wet season. The treatments, which showed positive yield trend, also showed positive total P uptake trend. Positive yield trends were attributed to the increasing P supplying power of the soil.     

Rice Drying,Storage and Processing: Effects of Post-Harvest Operations on Grain Quality

Various post-harvest processes of rice are commonly employed, especially during the off-season, to ensure its consumption feasibility, which often affect the grain quality. Different forms of drying, storage and processing of rice are evaluated to identify their effects on grain quality. Microwave drying has emerged as an alternative to the widely-used intermittent-drying and fixed-bed-dryer methods of drying paddy rice. Control of drying-air temperatures (between 40 °C and 60 °C) according to the rice variety can improve quality, especially for exotic varieties. Keeping stored grain in hygroscopic balance, with water content between 11% to 15%, at temperatures between 16 °C and 20 °C and with intergranular relative humidity near 60%, allows 12 months of storage in a controlled environment without significant deterioration. Other innovations, notably the application of artificial refrigeration to grain stored in bulk in vertical cylindrical silos and the use of impermeable packaging for storage, ensure the conservation of grain mass. The different stages and equipments used to obtain polished, brown and parboiled rice result in significant changes in the nutritional value of rice because of the removal of the outermost layers of the grains. Polishing reduces the nutritional value and physical homogeneity of rice. Brown rice retains more bioactive compounds and nutrients because it does not lose the outer layer of the grains in the polishing processes. Parboiled rice, although less nutritious than brown rice, has better grain integrity and milling yield and less loss of nutrients than white rice.     

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat (Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha⁻¹) treatment around flowering at low (67 kg N ha⁻¹) and high (194 kg N ha⁻¹) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha⁻¹) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha⁻¹) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg⁻¹ (4.5%) for protein content, 3.2 cm³ (11.9%) for Zeleny sedimentation, and 20 g kg⁻¹ (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.     

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha⁻¹ for rice and 0, 60,120, and 180 kg N ha⁻¹ for wheat) on grain yield, N uptake, residual soil N_min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha⁻¹ for rice and >120 kg ha⁻¹ for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha⁻¹ and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N_min ranged from 66 to 88 kg N ha⁻¹ and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha⁻¹), but low N inputs resulted in a negative balance (−85 to −360 kg ha⁻¹). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha⁻¹) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.     

Submergence tolerance and yield performance of lowland rice as affected by agronomic management practices in eastern India

Rice is subjected to excessive waterlogging and flash-flooding on large areas in south and south-east Asia. Besides cultivars, submergence tolerance of plants is influenced by various agronomic practices. A field experiment was conducted at Cuttack, India during 1994–1995 to study the effect of method of stand establishment (direct seeding and transplanting), vigour of seed (low and high-density) or seedlings (N-fertilized and unfertilized), plant population (normal and 50% more) and N fertilizer (single basal and split application) on yield performance of lowland rice under conditions of natural submergence and simulated flash-flooding (impounding up to 90 ± 3 cm depth for 10 days at vegetative stage). Flooding reached a maximum depth of 80 cm in 1994 and 52 cm in 1995 under natural submergence. The crop performance was better in 1994 due to timely sowing in dry soil and delayed accumulation of water (43 days after sowing) than in 1995 when sowing was done late in saturated soil followed by early water accumulation (28 days after sowing). Grain yield of rice decreased by 30.0–33.6% due to simulated flash-flooding compared with natural submergence, and by 21.4–33.1% due to transplanting in July compared with direct seeding in May-end/early June. The yield of direct-sown crop increased by using high-density seed of 22.9–23.0 mg weight (5.2–9.0%), higher seed rate of 600 m⁻² (2.2–2.3%) and basal fertilization at 40 kg N ha⁻¹ (19.4–25.7%) compared with low-density seed (19.4–20.1 mg), 400 seed m⁻² and no N, respectively. The yield of transplanted crop increased by using N-fertilized seedlings of 0.49–1.65 g weight (29.5–38.5%), higher number of seedlings at 155 m⁻² (3.5–16.7%) and basal fertilization at 40 kg N ha⁻¹ (31.9–32.5%) compared with unfertilized seedlings (0.19–0.79 g), 115 seedlings m⁻² and no N. Split application of 40 kg N ha⁻¹ — 50% each at basal and top dressing (105–115 days of growth after flash-flooding) — improved yield significantly (10.1–13.1%) over single basal application under simulated flash-flooding, but not under natural submergence conditions. Regression analysis indicated that relative contribution of various factors in increasing grain yield was in order: N fertilizer > seed density > seed m⁻² in direct-sown rice, and N fertilizer > seedlings m⁻² > seedling dry weight in transplanted rice. It was concluded that grain yield of flood-prone lowland rice can be increased by establishing the crop early through direct seeding using high-density seed and basal N fertilization.     

Effect of N rate,timing and splitting and N type on bread-making quality in hard red spring wheat under rainfed Mediterranean conditions

Three different experiments were designed to study the effects of N fertilizer rate, timing and splitting, and the response to combined application of N and S fertilizer on the bread-making quality of hard red spring wheat (Triticum aestivum L.) over a 3-year period in Vertisols under rainfed Mediterranean conditions. The following parameters were analyzed: grain yield, test weight, grain protein content, gluten index and alveograph parameters (W: alveogram index; P: dough tenacity; L: dough extensibility; P/L: tenacity–extensibility ratio). The N rate experiment included rates of 0, 100, 150 and 200 kg N ha⁻¹ applied on four different sites. The experiment was designed as a randomized complete block with four blocks. For the experiment on N timing and splitting, a single rate of 150 kg N ha⁻¹ was used, different fractions being applied at sowing, tillering and stem elongation, at a single site; again, experimental design was a randomized complete block with four blocks. Finally, for the experiment on the response to combined application of N and S fertilizer, a single fertilizer dose of 150 kg N ha⁻¹ was applied in two forms (urea+ammonium nitrate and urea+ammonium nitrosulfate) with one leaf application at ear emergence (zero, 25 kg S ha⁻¹, 25 kg N ha⁻¹, $\text{25}\text{kg}\text{S}\text{ha}{}^{\mathrm{-1}}\text{+25}$ kg N ha⁻¹ and 50 kg N ha⁻¹), also at a single site, using a split-plot design with four replications. Year-on-year variation in rainfall led to marked variations in wheat yield, grain protein content and bread-making quality indices. A close correlation was observed between rainfall over the September–May period and both grain yield and grain protein content (optimum values for both being recorded in the rainfall range 500–550 mm) as well as the alveogram index. A negative correlation was observed between mean maximum temperatures in May and both test weight and alveogram index (W). N fertilizer rate had a more consistent effect on bread-making quality than on grain yield. The highest values for grain yield were recorded at an N rate of 100 kg ha⁻¹, while maximum grain protein content values were recorded at 150 kg ha⁻¹. Application of half or one-third of total fertilizer N at stem elongation improved grain yield and grain protein content with respect to applications at sowing alone or at both sowing and tillering. Increased N rates led to a considerable increase in W values and to a reduction in the P/L ratio, thus improving dough balance, with a negative effect on the gluten index. Leaf application of N at ear emergence only affected grain protein content and the W index. Soil or leaf application of S had no effect on protein quality indices. The response of grain yield and grain protein content to fertilizer N differed from that reported for temperate climates.     

Breeding Novel Short Grain Rice for Tropical Region to Combine Important Agronomical Traits,Biotic Stress Resistance and Cooking Quality in Koshihikari Background

Breeding program strategies to develop novel short grain white rice varieties such as japonica (short grain) that introgress biotic stress resistance and high grain quality have been developed using indica rice (Pin Kaset + 4 and Riceberry) for applications in japonica rice (Koshihikari) improvement. Four breeding lines showing promising agronomic performance with short grain and low amylose content (< 20%) were obtained. In addition, sensory testing of these breeding lines showed high scores that similar to Koshihikari. Two promising lines, KP48-1-5 and KP48-1-9, which possessed a combination of four genes resistance to different biotic stresses (Bph3 + TPS + Xa21 + Pi-ta) and four genes for grain quality (GS3 + SSIIa + wx^b + badh2), were developed using marker-assisted selection (MAS) with the pedigree method. The current study clearly illustrated the successful use of MAS in combining resistance to multiple biotic stresses while maintaining a high yield potential and preferred grain quality. Moreover, the results indicated that this breeding program, which includes crossing temperate japonica with indica, can create novel short grain rice varieties adapted to a tropical environment, like the japonica type.     

Silicon fertilization modulates 2-acetyl-1-pyrroline content,yield formation and grain quality of aromatic rice

Present study aimed to assess silicon (Si) mediated yield, grain quality and regulations in 2-acetyl-1-pyrroline accumulation (2-AP) in aromatic rice. Four different levels of Si at 15, 30, 45 and 60 mg kg⁻¹ were applied to two aromatic rice cultivars i.e., Nongxiang 18 and Meixiangzhan 2, while pots without Si were served as control (CK). Results revealed that Si fertilization improved 2-AP, Si and proline contents in leaves and grains as well as activities of proline dehydrogenase (PRODH) and net photosynthetic rates (Pn) (in leaves) while interfered with total N contents in leaves and grains. Moreover, leaves N and proline contents, and net photosynthetic rates (Pn) were decreased with plant age i.e., tillering > flowering > maturity while PRODH activities and Si contents were highest at flowering and maturity stages, respectively and minimum at tillering stage. Furthermore, growth, yield and quality components were also improved by Si application but results were not consistent regarding grain quality for both rice cultivars. Further, Si contents in leaves have significant positive relations (r = 0.3974, P < 0.05) with grain 2-AP contents at flowering stage. Hence, Si proved better for both rice cultivars whereas 2-AP contents were higher for Meixiangzhan 2 than Nongxiang 18.     

Seasonal changes in the effects of free-air CO2 enrichment (FACE) on dry matter production and distribution of rice (Oryza sativa L.)

It is reported that stimulating effect of elevated atmospheric [CO₂] on photosynthesis of rice (Oryza sativa L.) is likely to be reduced during the plant growth period. However, there is little information on seasonal changes in dry matter (DM) production and distribution of rice under elevated atmospheric [CO₂]. A free-air CO₂ enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003, using Wuxiangging 14, a japonica cultivar. The rice was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] and supplied with 25 g N m², which is the normal N application rate for local farmers. DM accumulation of rice in FACE plots was significantly increased by 40, 30, 22, 26 and 16% on average at tillering, panicle initiation (PI), heading, mid-ripening and grain maturity, respectively. Rice DM production under FACE was significantly enhanced by 41, 27, 15 and 38% on average during the growth periods from transplanting to tillering (Period 1), tillering to PI (Period 2), PI to heading (Period 3) and heading to mid-ripening (Period 4), respectively, but significantly decreased by 25% in the period from mid-ripening to grain maturity (Period 5). In general, seasonal changes in crop response to FACE in both green leaf area index (GLAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production. Under FACE the leaves decreased significantly in proportion to the total above-ground DM over the season, the stems showed an opposite trend, while the spikes depended on crop development stage: showing no change at heading, significant increase (+4%) at mid-ripening and significant decrease (−3%) at grain maturity. Grain yield was stimulated by an average of 13% by FACE, due to increased total DM production rather than any changes in partitioning to the grain. We conclude that the gradual acclimation of rice growth to elevated [CO₂] do not occur inevitably, and it could also be altered by environmental conditions (e.g., cultivation technique).     

Soil fertility management in irrigated rice systems in the Sahel and Savanna regions of West Africa: Part I. Agronomic analysis

Yield, input use, productivity and profitability of irrigated rice systems were analyzed based on surveys in Senegal (Thiagar and Guédé), Mali (Office du Niger) and Burkina Faso (Kou Valley). The objective was to determine agronomic factors contributing to farmers' fertilizer-use efficiency and productivity, given current farmer practices. (A second paper addresses profitability and risk issues). Grain yields were highly variable, within and across sites. Minimum grain yield was 0.2 t ha⁻¹ (Thiagar), maximum recorded grain yield was 8.7 t ha⁻¹ (Office du Niger). The yield gap between actual farmers' yield and simulated potential or maximum attainable farmers' yield ranged from 0.6 to 5.7 t ha⁻¹ (Kou), 1.8 to 8.2 t ha⁻¹ (Thiagar), 0.3 to 6.3 t ha⁻¹ (Office du Niger), 0.8 to 5.7 t ha⁻¹ (Guédé), indicating considerable scope for improved yield. Physiological nitrogen efficiency (δ grain yield/δ N uptake) was mostly between 40 and 80 kg grain kg⁻¹ plant N. Apparent recovery of fertilizer N was highly variable (average: 30–40% of applied N). Timing of N fertilizer application by farmers was extremely variable and often did not coincide with critical growth stages of the rice plant. Other agronomic constraints included: use of relatively old (>40 days) seedlings at transplanting (Kou, Office du Niger), P and/or K deficiency (Office du Niger), unreliable irrigation water supply (Kou, dry season), delayed start of the wet growing season resulting in yield losses of up to 20% due to cold-induced spikelet sterility (Kou, Guédé, Office du Niger), weed problems (Thiagar), and late harvesting (Thiagar). Discussions during meetings with farmers at the survey sites revealed that farmers lacked knowledge on (i) optimal timing, dosage and mode of fertilizer application, (ii) optimal sowing dates to avoid yield loss due to cold- or heat-induced sterility, and (iii) the importance of N as the main limiting factor to yield. Possibilities to achieve a sustainable increase in rice productivity and profitability in West African irrigation systems are discussed.     

Effect of Milling and Parboiling Processes on Arsenic Species Distribution in Rice Grains

This study identified the role of milling and parboiling on arsenic (As) content and its species in large numbers of rice samples. Total As contents were 108 ± 33 μg/kg in polished rice grains (PR), 159 ± 46 μg/kg in unpolished rice grains (UR), 145 ± 42 μg/kg in parboiled polished rice grains (PPR) and 145 ± 44 μg/kg in parboiled unpolished rice grains (PUR). The percentages of inorganic As (iAs) were 66% ± 8% in PR and from 72% to 77% in other grain categories. The polishing process reduced the As content in the rice grains, removing outer part of the UR with high amount of As, whereas the parboiling technique transferred the semimetal content within the grain. Total As and iAs contents were not significantly different in UR, PPR and PUR, homogenizing its distribution inside the grains. The results allowed to understand how different operations affect As fate and its chemical forms in grains.     

Variation within a bread wheat cultivar for grain yield,protein content,carbon isotope discrimination and ash content

The study was undertaken to assess the variation within a bread wheat (Triticum aestivum L.) cultivar, primarily for grain yield, and the implications for wheat breeding. During the 1998–1999 growing season, cv. Nestos was established in a non-replicated (NR-0) honeycomb experiment, in the absence of competition (11 547 plants ha⁻¹). Ten high yielding (H) and 10 low yielding (L) plants were selected, the seeds of which were used to form the respective H and L lines. The 20 lines, along with their original cultivar, were evaluated in two locations either in the absence of competition (11 547 plants ha⁻¹) during the 1999–2000 season or under competition (5 000 000 plants ha⁻¹) during the 2000–2001 season. Results showed significant differentiation between lines for grain yield, determined both in the absence of competition at the single-plant level, i.e. yield per plant (YP), and under competition at the crop yield level, i.e. yield per plot (CY). Significant differences between lines were also found for grain protein content (PC), grain carbon isotope discrimination (Δ), and grain ash content (ASH), either in the absence of competition or under competition. A positive relationship was found between YP and CY (r=0.53,P<0.02). Results showed that selection within a bread wheat cultivar, under very low density and on the basis of individual plant grain yield, could be an effective way to either upgrade or maintain the cultivar, whereas the use of Δ or ASH as indirect selection criteria instead of grain yield was not supported by the study.     

Responses of sunflower yield and grain quality to alternating day/night high temperature regimes during grain filling: Effects of timing,duration and intensity of exposure to stress

In order to quantify the effects, at different stages during grain filling, of alternating day/night high temperature regimes on sunflower grain yield and quality, heads were exposed to high temperatures during 7 or 6 days starting either 10–12 days after anthesis (daa, HT1), 18 daa (HT2) or 24 daa (HT3). Also, heads were exposed to high temperatures for periods of 2, 4 or 6 days in each of HT1 and HT2. Temperatures covered a range of mean daily grain temperature of 20–40 °C and peak grain temperatures (i.e., those prevailing during the central 5 h of the daylight period) of 26–45 °C. High temperature stress for periods of 4 days or longer produced significant (p < 0.05) reductions in grain yield and grain quality. Early (HT1) exposure to stress reduced yield by 6%/°C above a mean grain temperature threshold of 29 °C; later (HT2 + HT3) exposures reduced yield by 4%/°C above a threshold of 33 °C. These reductions in yield were attributable to reductions in unit grain weight at all positions (periphery, intermediate, central) on the head, and an increase in the proportion of very small (10–30 mg) grains, termed half-full (HF) grains in this paper. In both full and HF grains, stress in either HT1 or HT2 reduced final pericarp weight, associated with fewer number of cell layers and thinner cell walls in the schlerenchyma. High temperatures reduced both the rate and duration of oil deposition in the grain, with the greatest effects being found with early (HT1) exposures. The unsaturation (oleic acid/linoleic acid) ratio of oil from mature grain was altered only when exposure to heat stress overlapped with the cessation of deposition of storage lipids. The effects of duration and intensity of heat stress on relative (to control) grain yield and oil content could be reasonably summarized using a linear response to cumulative hourly heat load calculated with a base temperature of 30 °C. We conclude that: (i) 4 days of alternating day/night temperatures resulting in mean daily grain temperatures of >30 °C can reduce sunflower grain yield and quality; (ii) the magnitude of these effects is strongly dependent on the timing of exposure and their nature on the grain growth processes active at the time of stress; and (iii) an hourly heat load (base = 30 °C) provides a useful integrative estimator of the effects of exposure to heat stress on grain yield and oil content for a given phase of grain filling.     

Effects of clear plastic film mulch on yield of spring wheat

This paper explores the possibility of improving yields of spring wheat (Triticum aestivum) by using plastic film mulching. Field experiments compared three mulching treatments viz. for 20 d (M1), 40 d (M2), and 60 d (M3) after sowing (DAS), with a non-mulch control (CK). Mulching increased temperature and moisture in the upper 5 cm of soil, and shoots emerged 8 d earlier than in CK. Mulching also increased number of tillers, length of the growing period, spikelet and grain numbers per spike, and the duration from flowering to harvest. In the mulched treatments, photosynthesis rate and soluble sugar content were higher in the vegetative period, but soluble sugar content was lower in the grain filling period relative to CK. Grain yield following 20 d mulching was greatest (8207 kg ha⁻¹), and decreased gradually as the mulching period increased (7847 and 6702 kg ha⁻¹ for M2 and M3, respectively). Plastic film removed after 20 d maximizes yield and minimizes soil pollution.     

Responses of field-grown irrigated rice cultivars to varying levels of floodwater salinity in a semi-arid environment

Shallow saline water tables, naturally saline soils and variations in climatic conditions over the two growing seasons, create a harsh environment for irrigated rice production in the Senegal River Delta. At the onset of the growing season, salts accumulated by capillary rise in the topsoil are released into the soil solution and floodwater. Rice fields often lack drainage facilities, or drain from one field to the other, thus building up salt levels during the season. Salt stress may, therefore, occur throughout the growing season and may coincide with susceptible growth stages of the rice crop. The objectives of the present study were to (i) determine varietal responses to seasonal salinity in both the hot dry season (HDS) and the wet season (WS) and (ii) derive guidelines for surface water drainage at critical growth stages. We evaluated responses of three rice cultivars grown in the region to floodwater salinity (0–2, 4, 6, 8 mS cm⁻¹), applied either at germination, during 2 weeks at crop establishment, during 2 weeks around panicle initiation (PI), or during 2 weeks around flowering. Floodwater electrical conductivity (EC) reduced germination rate for the most susceptible cultivar by as much as 50% and yield by 80% for the highest salinity level imposed. Salinity strongly reduced spikelet number per panicle, 1000 grain weight and increased sterility, regardless of season and development stage. The strongest salinity effects on yield were observed around PI, whereas plants recovered best from stress at seedling stage. Floodwater EC <2 mS cm⁻¹ hardly affected rice yield. For floodwater EC levels >2 mS cm⁻¹, a yield loss of up to 1 t ha⁻¹ per unit EC (mS cm⁻¹) was observed for salinity stress around PI (at fresh water yields of about 8 t ha⁻¹). Use of a salinity tolerant cultivar reduced maximum yield losses to about 0.6 t ha⁻¹ per unit EC. It is concluded that use of salinity tolerant cultivars, drainage if floodwater EC >2 mS cm⁻¹ at critical growth stages, and early sowing in the WS to avoid periods of low air humidity during the crop cycle, are ways to increase rice productivity in the Senegal River Delta.     

Effect of SWD irrigation on photosynthesis and grain yield of rice (Oryza sativa L.)

A study was conducted with the objective to determine the influence of (shallow water depth with wetting and drying) SWD on leaf photosynthesis of rice plants under field conditions. Experiments using SWD and traditional irrigations (TRI) were carried out at three transplanting densities, namely D1 (7.5 plants/m²), D2 (13.5 plants/m²) and D3 (19.5 plants/m²) with or without the addition of organic manure (0 and 15 t/ha). A significant increase in leaf net photosynthetic rate by SWD was observed with portable photosynthesis systems in two independent experiments. At both flowering and 20 DAF stages, photosynthetic rate was increased by 14.8% and 33.2% with D2 compared to control. SWD significantly increased specific leaf weight by 17.0% and 11.8% over the control at flowering and 20 DAF stages, respectively. LAI of D2 under SWD was significantly increased by 57.4% at 20 DAF. In addition, SWD with D2 significantly increased the leaf dry weight (DW) at both growing stages. At all the three densities, SWD increased the leaf N content and the increase was 18.9% at D2 density compared with the conventional control. In SWD irrigation, the leaf net photosynthetic rate was positively correlated with the leaf N content (R² = 0.9413), and the stomatal conductance was also positively correlated with leaf N content (R² = 0.7359). SWD enhanced sink size by increasing both panicle number and spikelet number per panicle. The increase in spikelet number per panicle was more pronounced in the 15 t ha⁻¹ manure treatment than in the zero-manure treatment. Grain yield was also significantly increased by SWD, with an average increase of 10% across all treatments. SWD with D2 had the highest grain yield under the both cultivars with or without 15 t ha⁻¹ manure treatment, which was 14.7% or 13.9% increase for Liangyoupeijiu and 11.3% or 11.2% for Zhongyou 6 over the control, respectively.     

Low temperature increased the biosynthesis of 2-AP,cooked rice elongation percentage and amylose content percentage in rice

Rice fragrance, cooked rice elongation and amylose content are some of the traits used in determining rice grain quality. 2-acetyl-1-pyrroline (2-AP) is the major compound that is responsible for fragrance in rice.This experiment was conducted with two indica rice cultivars: Meixiangzhan 2 and Xiangyaxiangzhan. Three temperature-controlled chambers: High (32 °C from 06:00 to 17:59 and 26 °C from 18:00 to 05:59), medium (27 °C from 06:00 to 17:59 and 21 °C from 18:00 to 05:59) and low (22 °C from 06:00 to 17:59 and 16 °C from 18:00 to 05:59) were used for the study. At the onset of heading, both cultivars were transferred to the three temperature-controlled chambers. Our results showed that in both cultivars, low temperature growth had the highest 2-AP content, while high temperature growth recorded the lowest 2-AP content. Principal component analysis showed remarkable differences in the metabolomes of rice grown in high, medium and low regimes. In the grains of both cultivars, we observed significant reduction in 2-AP content after 6 and 9 months of storage, however; 2-AP retention differed greatly in both cultivars. We also reported that low temperature growth increased cooked rice elongation percentage and the biosynthesis of amylose in rice. In conclusion, our findings will provide more information to breeders working on the improvement of rice grain quality.