Decrease In Number Of Grains Research Articles

Low seed rate in square planting arrangement has neutral or positive effect on grain yield and improves grain nitrogen and phosphorus uptake in wheat

Wheat (Triticum aestivum) has a high capacity to compensate grain yield (GY) at lower seed rates than those commonly assumed, especially in high-yield-potential environments. Our study aimed at assessing: (i) the response of GY, biomass and harvest index of wheat under two contrasting seed rates; (ii) trade-offs among yield components in response to seed rate; and (iii) the sensitivity of grain and crop N and P content and nutrient use efficiency under conventional and low seed rates in the high-yielding environment of southern Chile. We evaluated two wheat cultivars —Bacanora (higher grain number and intermediate grain weight) and Kambara (lower grain number and higher grain weight)— at two seed rates, a farmers’ seed rate of 350 plants m −2 (CON) and low seed rate of 44 plants m −2 with square grid planting arrangement (LSR), under optimum crop management conditions during two growing seasons in southern Chile (Valdivia). We evaluated GY and its components, as well as nitrogen (N) and phosphorus (P) economies. Contrasting results were found between cultivars under LSR. Bacanora fully compensated GY components reaching the same GY under both LSR and CON treatments, while Kambara yielded 12% more under the LSR treatment, compared with that of the CON treatment. The LSR treatment decreased the plant height of both cultivars by 0.14 m (19% and 15% in Bacanora and Kambara, respectively), which improved the harvest index. Under the LSR treatment, Bacanora showed a small decrease in grain number while there was no effect in Kambara. Both cultivars reached higher (P < 0.001) average grain weight under the LSR treatment. Furthermore, Bacanora increased grain N concentration and both cultivars improved grain P concentration under the LSR treatment. P uptake and P uptake efficiency were increased (P < 0.001 and P < 0.01, respectively) under the LSR treatment in both cultivars by 18%. Low seed rate (44 pl m −2 ) with square grid planting distribution results in preserved or increased wheat GY compared with the conventional seed rate (350 pl m −2 ), mainly due to an increase in grain weight in both genotypes. The LSR treatment resulted in decreased plant height, allowing an improved harvest index. Additionally, LSR had also a positive effect on grain P concentration, and a remarkably increased of both P uptake and P uptake efficiency. Our results offer an opportunity to increase the uptake of nutrients such as P, without any GY penalty and may even increase yields, at least in high yield environments, such as southern Chile. • Low seed rate (44 plants m −2 ) with a square grid planting arrangement preserved or increased wheat grain yield. • Low seed rate treatment increased grain weight (15%) and grain nutrient concentrations (N: 13%; P: 13%). • Harvest index increased under the low seed rate treatment. • Nitrogen yield and nitrogen harvest index increased under the low seed rate treatment. • Phosphorus uptake and phosphorus uptake efficiency increased under the low seed rate treatment.

Response of a U.S. rice hybrid variety to high heat at Two CO2 concentrations during anthesis and grainfill

Changing climate conditions are influencing quality and yield of the United States rice (Oryza sativa L.) export industry. The occurrence of high heat episodes, along with rising atmospheric carbon dioxide (CO2), is of particular concern for as-yet uncharacterized hybrid varieties. A popular rice hybrid was grown in soil-plant-atmosphere-research (SPAR) chambers under two CO2 levels (450 or 740 ppm) and subjected to one of three day/night temperature regimes during anthesis and grainfill: a control temperature (T) (0C) of 28/22°C, and a +4° (4C) or +8°C (8C) increase. There was little difference in biomass between 0 and 4C levels; however, yields at the 8C level declined by over 50%, by about 28 or 34 g plant−1°C−1 for ambient or elevated CO2 grown rice, respectively. There was little difference in fraction of biomass allocated among leaf, stem or panicle at 0 or 4C, but the proportion declined by about 31% to the panicles at 8C. Total productive tiller numbers and grainfill percentages were similar across CO2 levels at each T treatment such that yield declines were associated primarily with a decrease in grain number and mass. Slightly higher values for yield and harvest index were observed under elevated CO2 at the 3 T levels which was attributed to an average 10 mg increase in single grain weight. An interaction of CO2 and T on chalk content was observed, with expression at the +4°C treatment 11% higher for elevated versus ambient CO2; however, chalk expression was similar for CO2 levels at the +8°C treatment. Breeding efforts associated with climate resiliency should consider traits associated with hybrid vigor as well as high temperature resistance for grain sterility and quality factor responses.

Genetic analysis and gene mapping of bgl, a gene controlling grain length and quality in rice

Grain size is one of the important agronomic traits that determine rice yield. Map-based cloning of rice grain size-related genes impacts the genetic regulation mechanism of rice yield formation. Here we identified bgl mutant in rice which exhibits increase in grain length and panicle length with the decrease in number of grains per panicle and no observable difference in grain thickness and number of tillers as compared to the wild type (WT). Scanning electron microscopy observation of bgl mutant spikelets hull indicates an upsurge in number of external epidermal cells in a longitudinal way than the WT. Hence, it is likely that the long-grain phenotype was due to increased cell number longitudinally. Starch granule in both bgl and WT were large, sporadically polyhedral and densely packed, indicating no differences, signifying that both bgl mutant and WT have less chalkiness content. Genetic analysis showed that the bgl mutant was controlled by a recessive single gene, and was finely located on chromosome 3 through map-based cloning, within a physical distance of 40kb. Sequencing analysis revealed A to T substitution in the seventeen exons of LOC_Os03g44500 resulted in an amino acid change from Tryptophan (Try) to Phenylalanine (Phe). Taken together bgl mutant has a pleiotropic effect on grain yield and grain quality.

Trehalose can alleviate decreases in grain number per spike caused by low‐temperature stress at the booting stage by promoting floret fertility in wheat

AbstractAlleviating the negative effects of low temperature at the booting stage on wheat grain number and yield is important for maintaining high and stable wheat yields. In this study, we selected wheat varieties with different levels of cold resistance, simulated low temperature at the booting stage and exogenously applied trehalose to study its effect on wheat floret development under low‐temperature stress and explore the physiological mechanism of that process. The results showed that higher levels of endogenous trehalose benefited wheat resistance to low‐temperature stress. Exogenous trehalose inhibited floret degeneration and increased floret fertility in the apical spikelets, thus significantly alleviating the decrease in grain number per spike caused by low temperature. The results of the metabolomics analysis as well as the physiological indexes showed that trehalose significantly promoted the assimilation of nitrogen in florets under low‐temperature stress, thus reducing the accumulation of ammonium ions in the plant cells. In addition, exogenous trehalose significantly increased the endogenous spermidine level in florets, increased their glutathione and ascorbic acid contents, promoted the glutathione‐ascorbic acid cycle, and thereby reduced the contents of reactive oxygen species in florets. This may be an important physiological mechanism by which trehalose alleviates the effect of low‐temperature stress on floret development in wheat.

Activities of leaf and spike carbohydrate-metabolic and antioxidant enzymes are linked with yield performance in three spring wheat genotypes grown under well-watered and drought conditions

BackgroundTo improve our understanding about the physiological mechanism of grain yield reduction at anthesis, three spring wheat genotypes [L1 (advanced line), L2 (Vorobey) and L3 (Punjab-11)] having contrasting yield potential under drought in field were investigated under controlled greenhouse conditions, drought stress was imposed at anthesis stage by withholding irrigation until all plant available water was depleted, while well-watered control plants were kept at 95% pot water holding capacity.ResultsCompared to genotype L1 and L2, pronounced decrease in grain number (NGS), grain yield (GY) and harvest index (HI) were found in genotype L3, mainly due to its greater kernel abortion (KA) under drought. A significant positive correlation of leaf monodehydroascorbate reductase (MDHAR) with both NGS and HI was observed. In contrast, significant negative correlations of glutathione S-transferase (GST) and vacuolar invertase (vacInv) both within source and sink were found with NGS and HI. Likewise, a significant negative correlation of leaf abscisic acid (ABA) with NGS was noticed. Moreover, leaf aldolase and cell wall peroxidase (cwPOX) activities were significantly and positively associated with thousand kernel weight (TKW).ConclusionDistinct physiological markers correlating with yield traits and higher activity of leaf aldolase and cwPOX may be chosen as predictive biomarkers for higher TKW. Also, higher activity of MDHAR within the leaf can be selected as a predictive biomarker for higher NGS in wheat under drought. Whereas, lower activity of vacInv and GST both within leaf and spike can be selected as biomarkers for higher NGS and HI. The results highlighted the role of antioxidant and carbohydrate-metabolic enzymes in the modulation of source-sink balance in wheat crops, which could be used as bio-signatures for breeding and selection of drought-resilient wheat genotypes for a future drier climate.

Suppressed ABA signal transduction in the spike promotes sucrose use in the stem and reduces grain number in wheat under water stress

Water stress is a primary trigger for reducing grain number per spike in wheat during the reproductive period. However, under stress conditions, the responses of plant organs and the interactions between them at the molecular and physiological levels remain unclear. In this study, when water stress occurred at the young microspore stage, RNA-seq data indicated that the spike had 970 differentially expressed genes, while the stem, comprising the two internodes below the spike (TIS), had 382. Abscisic acid (ABA) signal transduction genes were down-regulated by water stress in both these tissues, although to a greater extent in the TIS than in the spike. A reduction in sucrose was observed, and was accompanied by increases in cell wall invertase (CWIN) and sucrose:sucrose 1-fructosyl-transferase (1-SST) activities. Hexose and fructan were increased in the TIS but decreased in the spike. ABA was increased in the spike and TIS, and showed significant positive correlation with CWIN and 1-SST activities in the TIS. Overall, our results suggest that water stress induces the conversion of sucrose to hexose by CWIN, and to fructan by 1-SST, due to increased down-regulation of ABA signal transduction related-genes in the TIS; this leads to deficient sucrose supply to the spike and a decrease in grain number.

Effects of water deficit on breadmaking quality and storage protein compositions in bread wheat (Triticum aestivum L.).

Water deficiency affects grain proteome dynamics and storage protein compositions, resulting in changes in gluten viscoelasticity. In this study, the effects of field water deficit on wheat breadmaking quality and grain storage proteins were investigated. Water deficiency produced a shorter grain-filling period, a decrease in grain number, grain weight and grain yield, a reduced starch granule size and increased protein content and glutenin macropolymer contents, resulting in superior dough properties and breadmaking quality. Reverse phase ultra-performance liquid chromatography analysis showed that the total gliadin and glutenin content and the accumulation of individual components were significantly increased by water deficiency. Two-dimensional gel electrophoresis detected 144 individual storage protein spots with significant accumulation changes in developing grains under water deficit. Comparative proteomic analysis revealed that water deficiency resulted in significant upregulation of 12 gliadins, 12 high-molecular-weight glutenin subunits and 46 low-molecular-weight glutenin subunits. Quantitative real-time polymerase chain reaction analysis revealed that the expression of storage protein biosynthesis-related transcription factors Dof and Spa was upregulated by water deficiency. The present results illustrated that water deficiency leads to increased accumulation of storage protein components and upregulated expression of Dof and Spa, resulting in an improvement in glutenin strength and breadmaking quality. © 2018 Society of Chemical Industry.

Non-destructive, high-content analysis of wheat grain traits using X-ray micro computed tomography

BackgroundWheat is one of the most widely grown crop in temperate climates for food and animal feed. In order to meet the demands of the predicted population increase in an ever-changing climate, wheat production needs to dramatically increase. Spike and grain traits are critical determinants of final yield and grain uniformity a commercially desired trait, but their analysis is laborious and often requires destructive harvest. One of the current challenges is to develop an accurate, non-destructive method for spike and grain trait analysis capable of handling large populations.ResultsIn this study we describe the development of a robust method for the accurate extraction and measurement of spike and grain morphometric parameters from images acquired by X-ray micro-computed tomography (μCT). The image analysis pipeline developed automatically identifies plant material of interest in μCT images, performs image analysis, and extracts morphometric data. As a proof of principle, this integrated methodology was used to analyse the spikes from a population of wheat plants subjected to high temperatures under two different water regimes. Temperature has a negative effect on spike height and grain number with the middle of the spike being the most affected region. The data also confirmed that increased grain volume was correlated with the decrease in grain number under mild stress.ConclusionsBeing able to quickly measure plant phenotypes in a non-destructive manner is crucial to advance our understanding of gene function and the effects of the environment. We report on the development of an image analysis pipeline capable of accurately and reliably extracting spike and grain traits from crops without the loss of positional information. This methodology was applied to the analysis of wheat spikes can be readily applied to other economically important crop species.

Water deficit stress tolerance in maize conferred by expression of an isopentenyltransferase (IPT) gene driven by a stress- and maturation-induced promoter

Senescence can be delayed in transgenic plants overexpressing the enzyme isopentenyltransferase (IPT) due to stress-induced increased levels of endogenous cytokinins. This trait leads to sustained photosynthetic activity and improved tolerance to abiotic stress. The aim of this study was to generate and characterize transgenic plants of maize (Zea mays L.) transformed with the IPT gene sequence under the regulation of SARK promoter (protein kinase receptor-associated senescence). Three independent transgenic events and their segregating null controls were evaluated in two watering regimes (WW: well watered; WD: water deficit) imposed for two weeks around anthesis. Our results show that the WD treatment induced IPT expression with the concomitant increase in cytokinin levels, which prolonged the persistence of total green leaf area, and maintained normal photosynthetic rate and stomatal conductance. These trends were accompanied by a minor decrease in number of grains per plant, individual grain weight and plant grain yield as compared to WW plants. Plants expressing the IPT gene under WD had PGR, anthesis and silking dates and biomass levels similar to WW plants. Our results demonstrate that expression of the IPT gene under the regulation of the SARK promoter helps improve productivity under WD conditions in C4 plants like maize.

Identifying traits leading to tolerance of wheat to Septoria tritici blotch

Identifying tolerance traits to diseases in wheat genotypes has an increased interest to minimize pesticide use and to complement resistance and escape.Yield tolerance to Septoria tritici blotch (STB) was studied pooling up three experiments involving 18 genotypes, 5 years and 6 sites in France, amounting to 161 genotype×year×site×management combinations. Each combination involves a crop pair (treated or not against foliar diseases) repeated two to three times. Most crops were grown under high fertilization, and STB was the main disease present in untreated crops. Crop traits (ear density, grain number and weight, area of leaf laminas) were recorded; green area of leaf laminas over time was fitted to a Gompertz equation, producing metrics for senescence traits (time and duration).Over the whole dataset, LAI from 1.1 to 7.5m2m−2; yields from 280 to 1122gDMm−2 and relative yield losses up to 70% were recorded. Fungicide treated crops exhibited slightly larger ear density and leaf lamina area independently of the intensity of epidemics. As an overall trend, yield became more determined by source traits when epidemics occurred. Yield loss was proportional (r2=0.7) to senescence advance by disease. Decrease in grain number and weight were also correlated (r2=0.4 and 0.8, respectively) to yield loss. Two epidemic indices were built to compare data across year×site combinations. Then yield in untreated crop was predicted (r2=0.87) from yield in corresponding treated crop, and interaction of epidemic indices with traits of the treated crops that therefore were pointed out as responsible for tolerance variability. Late senescing crops exhibited a greater tolerance to epidemics. Conversely, grain weight was a major key of intolerance. To minimize the trade-off between yield potential and tolerance it is thus suggested to maximize grain number.This study represents a first step in identifying key traits involved in tolerance to STB in varying agronomic conditions and cultivars.

Heat Stress at Different Grain Filling Stages Affects Fresh Waxy Maize Grain Yield and Quality

The effects of heat stress (mean day/night temperatures were 29/18 and 35/18°C for control and heat stress treatments, respectively) at 1–10 or 11–20 days after pollination (DAP) on grain yield and quality of two waxy maize varieties, Suyunuo5 and Yunuo7, were studied. The decrease in grain number and fresh grain yield was more severe when heat stress was introduced early. The responses of grain weight and its components to heat stress were dependent on the variety and heat stress stage. Heat stress increased the starch granule size and volume percentage of diameter larger than 17 μm in both varieties. Crystallinity, iodine binding capacity, and pasting and gelatinization temperatures were increased in both varieties under heat stress at 11–20 DAP; however, the response to early‐stage heat stress was variety dependent. Peak viscosity and retrogradation percentage were increased by heat stress at either stage. These results suggest that heat stress decreases fresh grain yield and accelerates grain filling rate; it increases starch content, starch granule size, crystallinity, and iodine binding capacity as well as decreases the protein content in Yunuo7, thus making the grain less tender and prone to retrogradation. Warm conditions should shorten the time to harvest in fresh waxy maize production.

Undersowing wheat with different living mulches in a no-till system. I. Yield analysis

The classical management of no-till wheat has several environmental and economic drawbacks such as the use and cost of herbicides, and the degradation of soil physical quality. Recent investigations suggest that undersowing crops with a living mulch could be a sustainable alternative. Therefore, we studied during three growing seasons the effect of undersowing wheat with living mulches on wheat grain yield. Treatments were wheat grown on a conventionally-tilled soil, on a no-till soil, and on a no-till soil with various living mulches. The living mulches were red fescue, sheep’s fescue, alfalfa, bird’s-foot-trefoil, black medic and white clover. Our results show that the use of living muches during wheat cropping decreased wheat yield of 19–81% by comparison with wheat cropped alone. This decrease is linked to the biomass of living mulches and weeds at the time of flowering. As a consequence, the control of living mulch and weed biomass is a major issue. Our findings also reveal that the wheat yield decrease is mainly the consequence of a decrease in grain number from 37 to 32 grains per spike on average, and of a decrease in spike number from 0.7 to 0.4 spikes per stem. We thus conclude that stem elongation, flowering and fecundation are the major stages of stress for wheat grown with living mulches. Our findings will help to design innovative crop management systems that take into account the biological interactions in agro-ecosystems better.

Effects of elevated CO2 and O3 on the rate and duration of grain growth and harvest index in spring wheat (Triticum aestivum L.)

AbstractWheat (Triticum aestivum L.) cv. Minaret was grown in open‐top chambers (OTCs) in 1995 and 1996 under three carbon dioxide (CO2) and two ozone (O3) levels. Plants were harvested regularly between anthesis and maturity to examine the rate of grain growth (dG/dt; mg d–1) and the rate of increase in harvest index (dHI/dt;% d–1). The duration of grain filling was not affected by elevated CO2 or O3, but was 12 days shorter in 1995, when the daily mean temperature was over 3 °C higher than in 1996. Season‐long exposure to elevated CO2 (680 μmol mol–1) significantly increased the rate of grain growth in both years and mean grain weight at maturity (MGW) was up to 11% higher than in the chambered ambient air control (chAA; 383 μmol mol–1). However, the increase in final yield obtained under elevated CO2 relative to the chAA control in 1996 resulted primarily from a 27% increase in grain number per unit ground area. dG/dt was significantly reduced by elevated O3 under ambient CO2 conditions in 1995, but final grain yield was not affected because of a concurrent increase in grain number. Neither dG/dt nor dHI/dt were affected by the higher mean O3 concentrations applied in 1996 (77 vs. 66 nmol mol–1); the differing effects of O3 on grain growth in 1995 and 1996 observed in both the ambient and elevated CO2 treatments may reflect the contrasting temperature environments experienced. Grain yield was nevetheless reduced under elevated O3 in 1996, primarily because of a substantial decrease in grain number. The data obtained show that, although exposure to elevated CO2 and O3 individually or in combination may affect both dG/dt and dHI/dt, the presence of elevated CO2 does not protect against substantial O3‐induced yield losses resulting from its direct deleterious impact on reproductive processes. The implications of these results for food production under future climatic conditions are considered.

The role of grain number, nitrogen nutrition and stem number in limiting pea crop ( Pisum sativum) yields under agricultural conditions

In a small area of the Paris basin in France, 71 pea ( Pisum sativum) crops, cv. Solara, were examined to elucidate the determinants of their yield over 3 years. The yields ranged from between 3.71 and 7.81 t ha −1, and averaged 5.85, 6.25 and 6.47 t ha −1 in 1988, 1989 and 1990, respectively. The large differences observed each year among fields were essentially related to grain number, whereas mean grain weight was less variable. Grain number and pod number were highly correlated. A substantial effect of nitrogen nutrition, assessed by a nitrogen nutrition index on grain number, was observed. The role of reproductive stem number on grain number was also examined, showing a threshold at 115 stems m −2, below which, under the conditions examined, large grain numbers per stem did not compensate for low stem numbers. Furthermore, we also show that branching might not be sufficient to compensate for low plant numbers in some crops when nitrogen nutrition is inadequate, and this also leads to a decrease in grain number.

Effects of competition with weeds on the growth, development and yield of sorghum

SUMMARYIn two field experiments in Suriname, competition between weeds and sorghum (Sorghum bicolor(L.) Moench) was studied in the rainy seasons of 1982 and 1983. The crop was kept either weed-free or without weed control for each of six different periods of time from planting. Observations made at the end of each period allowed an analysis to be made of the growth and development of a crop with and without weed control.Due to the crop canopy structure and fertilizer placement near the row, weed growth was concentrated in the rows. Starting atc.20–30 days after planting, competition with weeds reduced ground-cover and leaf area index of the crop. Competition reduced growth rates, leading to lower yields. Plant population density was not affected, but competition reduced the number of leaves present. Stem length initially increased with competition in one season, but was retarded in another. Competition for nutrients was strong and was found as early as 15 days after planting. Nitrogen was the element most competed for initially. Competition for water occurred, but competition for light seemed unlikely. About 20 weed-free days after planting were necessary to avoid yield losses and around 30 weed-free days to attain negligible weed growth at harvest. Yield reduction was mainly due to a decrease in number of grains per panicle. Competition during floret establishment (c.30–40 days after planting) should be avoided.

Use of foliar-applied urea to inhibit the development of Septoria nodorum in spring wheat

This study was carried out to provide more detailed information about the toxicity of foliar-applied urea on the development of the fungus Septoria nodorum Berk. in wheat, and to examine the interaction between urea and infection on the formation of yield components and grain protein properties. Greenhouse and field experiments involved spring wheat cv. Ruso, which is very susceptible to leaf and glume blotch caused by S. nodorum. Urea solution effectively prevents the development of Septoria infection when applied before inoculation. An agar-plate assay indicated that urea solution > 5% strongly inhibits colony growth. Urea seems to be phytotoxic only if leaf tissue is wetted for an extended period with the solution in the greenhouse. This phytotoxicity would explain the observed decrease in number of grains per ear, ear weight, 1000-grain weight, as well as in residue protein and in SDS sedimentation volume. However, no phytotoxicity and negative effects on yield components and protein properties were observed after urea spray under field conditions. Urea application caused a 0.01–0.04 pmol/100 μl increase in abscisic acid concentration in plant tissue.

The Effect of Speckled Leaf Blotch on Apical Development and Yield in Winter Wheat in New Zealand

Speckled leaf blotch (Mycosphaerella graminicola) reduced yield in a winter wheat trial by 18 per cent. Detailed analyses of the effects of disease on yield components showed that disease reduced both grain number per ear and grain weight. The reduction in grain number per ear was due to a decrease in grain number per spikelet, and this occurred for both main stem and tillers, and occurred equally at each spikelet position on the ear. The effect of disease on grain number was traced back to an earlier reduction in floret primordium number per ear, especially floret number per spikelet. It was suggested that floret primordium production was affected by the reduced assimilate supply to the developing apex. The effects of disease on yield could therefore be attributed to effects on plant development both before and after anthesis. The disease effects on yield were not necessarily associated with the time of maximum disease severity. Plots with the early phase of disease epidemic only showed a significant reduction in yield, but there was some evidence of compensation for early reductions to yield potential in the later-determined yield components. We suggest, therefore, that an effective disease-control programme must take into account the possible early effects of disease on yield potential.

ミズガヤツリの生活過程の解析と防除に関する研究

The author investigated the physiological and ecological characteristics of C. serotinus, a perennial weed in paddy fields, during its whole life cycle, together with agronomic and chemical methods of control, and designed an effective integrated control system. This study was carried out at Chiba Agricultural Experiment Station during the period from 1966 to 1976.1. The life cycle is divided into 4 stages, emergence, propagation, tuber formation, and preparation for emergence. Reproduction occurs by seeds, tubers, base of shoots, base of new shoot-tubers, and stolon, but mainly by tubers.2. Characteristics and factors affecting tuber sprouting were analysed. The results indicated that oxygen supply is the most important factor for tuber sprouting, and that, in the fields, soil moisture content exerts an important influence on emergence from tubers in relation to oxygen supply.3. Effect of temperature, fertilizer elements and light on the propagation was examined. Results showed that competition for nutrients between rice plants and C. serotinus may be one of the reasons for the retarded propagation in rice fields, but the major limiting factor for the propagation of C. serotinus is presumed to be light intensity, since in any case the propagation was more inhibited when the growth of rice plant was more active compared to that of the weed.4. Factors affecting tuber formation were examined. Day-length as well as temperature was found to be an important factor affecting tuber formation, it appeared and that the number of tubers is determined by the number of plants, and also by the factors affecting propagation of plants.5. To analyse the effects of C. serotinus on growth and yield of rice, C. serotinus was planted at different times and different densities in paddy fields under various methods of rice cultivation. The results indicate that the dominancy of rice plants in the competition for light with C. serotinus causes less crop damage by the weed. The yield component which contributed most to the rice yield reduction was the decrease in panicle number, followed by the decrease in grain number per panicle.6. With regard to agronomic control methods, the effect of plowing and puddling was examined. Turn-over plowing in winter was effective to kill reproductive organs. Puddling was highly effective in killing both overwintering organs and shoots that have sprouted at the time of puddling, by burying them in the soil. Puddling combined with turn-over plowing in winter killed about 80% of the reproductive organs. In the fields of early season rice cultivation, plowing immediately after the rice harvest was also very effective in preventing tuber formation. In this case, rotary plowing was more effective than turn-over plowing.7. As for the herbicidal control, soil treatment after rice transplanting, foliage treatment with paraquat prior to puddling, and foliage treatment after rice harvest were analysed, and their suitability for effective control was evaluated.8. Based on the above results, an integrated control system for transplanted early-season rice cultivation was designed as shown in Fig. 9.

Plant population and shading studies in barley

SUMMARYTwo barley experiments are described in which a range of plant populations were shaded during different periods of development. Shading during the ear development period caused considerable reductions in grain yield, largely by reducing the number of grains per ear. Shading during the grain-filling period caused no reduction in grain yield. It is suggested that under conditions of these experiments there was probably a potential surplus of carbohydrate available for grain filling and that grain yield was largely determined by the storage capacity of the ears. The importance of the number of grains per ear as an indicator of individual ear capacity is emphasized.The effects of plant population on grain yield and its components are also examined. It is concluded that the number of grains per ear is the component having greatest influence on the decrease in grain yield at above-optimum populations and attention is again drawn to the possible importance of ear capacity. It is argued that on an area basis the number of grains per unit area may give a good indication of ear capacity. Examination of this parameter shows a close relationship with grain yield per unit area for both the shading and population treatments. It is particularly evident that a decrease in grain yield at high populations was associated with a comparable decrease in the number of grains per unit area. It is suggested that this decrease in grain number may be due to a lower production of total dry matter during ear development rather than an unfavourable partitioning of this dry matter between the ear and the rest of the plant. This lower production of total dry matter is attributed to the crop growth rates of the higher populations having reached their peak and then having declined before the end of the ear development period. This crop growth rate pattern, through its effect on grain number per unit area, is put forward as the basic reason why, in the final crop, grain yield per unit area decreases at above-optimum populations.

Studies on the Cool Injury in Bean Plants : II. Effects of time and period of nitrogen application on the soybeans treated with low temperature before flowering

The previous paper indicated that high nitrogen (N) application during the low temperature treatment caused a considerable decrease of the pod setting rate and the fertility per cent of ovules. In this paper, the unfavorable effects of high N application on low temperature treated soybeans was examined for clarifying of the relationship between the N supply conditions including level, time and period of application, and the stage of flower development with solution culture method. Flower developing plants were treated with low temperature at 15°C for 15 days and compared with the plants grown under the control condition at 24°C-day19°C-night. The flowers used in this experiment were restricted in the number per node and the time of blooming. Variance analysis of the pod setting rate, fertility per cent and the number of ovules per pod gave the significance of the interaction at the 1% level between N supply conditions and temperature conditions. N application under the 24°C/19°C condition obtained better grain yield compared with N free plot; on the contrary, N supply accompanied with the low temperature treatment showed a decreasing tendency of the pod setting rate and of the fertility per cent. The pod setting rate of the plants treated with low temperature was closed related to the time of N application. N application before or during the first five days in the low temperature treatment caused a signiftcant decrease in comparison to the N free condition and the later application showed the less damage. However no difference was observed betwen the level supplied at l00 ppm and 40 ppm N. The fertility per cent of the plants treated with low temperature was decreased by N application and, especially, all plants showed a considerable decrease in the pod setting rate which were accompanied with a significant decline. But the relation between time of N application and the degree of injury was not so clear as seen in the pod setting rate. Fertile grains which were supposed to be in a constant number of flowers per plant were calculated in each plot. N supply from before the low temperature treatment, till five days after the end of the treatment, resulted in a decrease in grain number, particularly, before the period of treatment and during the earlier period of N application, caused the greater decrease.