Breaking Uniculm Growth Habit of Spring Cereals at High Latitudes by Crop Management. II. Tillering, Grain yield and Yield Components

Long days at high latitudes inhibit tillering of cereals and hence seeding rates of 500–700 seeds m⁻² are commonly used for spring wheat, barley and oats in Finland. Costs could be reduced by using a lower seeding rate in combination with crop management to produce more head-bearing tillers m⁻². This study was designed to assess possibilities of breaking the uniculm growth habit of spring cereals by (1) lowering the seeding rate from 600 to 300 seeds m⁻² and (2) manipulating tiller growth with early mechanical treatments to the crop (rolling, cutting) or chemical applications (foliar urea, CCC and GA). A low seeding rate and early application of foliar CCC at high latitudes, under good moisture conditions prior to heading, promoted 20% more head-bearing tillers and 6% higher grain yield than standard management practices. However, cultivars differed in their response to CCC. The advantageous effects of CCC at a low seeding rate were attributed to increase, over the controls, in contribution of head-bearing tillers to grain yield in wheat (cultivar Heta ), but more grains per head in oats (cultivar Veli ). Varietal recommendations for use of low seeding rate in combination with early CCC spraying should be examined further.     

Crop Management Effects on Pre-and Post-Anthesis Changes in Leaf Area Index and Leaf Area Duration and their Contribution to Grain Yield and Yield Components in Spring Cereals

Seasonal changes in leaf area index (LAI) and leaf area duration (LAD, i.e. LAI integrated over cumulated degree days) have a marked effect on crop productivity. Three case experiments were conducted at Suitia (60°11′N) and Viikki (60°13′N) Experimental Farms, University of Helsinki, Finland, to evaluate the possibilities of accelerating pre-an thesis expansion of leaf area and modifying pre- and post-anthesis LAD in spring cereals through crop management. Effects of time of incorporation of a green manure crop residue into the soil [conventional tillage (autumn ploughing and seed bed preparation in the spring), conservation tillage (sole spring tillage) with and without a green manure crop, common vetch (Vicia saliva I.)]and N fertilizer rate (0, 50, 100kg N ha^?1) on LAI and pre- and post-anthesis LAD in wheat (Triticum aestivum L.) were studied in exp I; green manuring (common vetch) and N fertilizer rate (0,40, 70,110,150kg N ha^?1) in barley (Hordeum vulgare L.), oat (Avena sativa L.), and wheat in exp II; and foliar application of chlormequat chloride (CCC) and ethephon in oat lines (dwarf, naked, modern, landrace) differing in canopy structure in exp III. Time of incorporation of the green manure crop residues into the soil (exp I), green manuring (exp II), N fertilizer rate (exps I and II), and selection for crop growth type (exp III), but not CCC and ethephon, modified LAI and LAD in spring cereals by affecting the rate of pre-anthesis expansion and post-anthesis reduction in leaf area rather than by markedly prolonging the growth period. High rates of N fertilizer accelerated expansion of leaf area, especially prior to stem elongation, and resulted in high pre-anthesis LAD due to enhanced tiller growth (exps I and II) and more tillers per main shoot (exp I). Green manuring increased leaf expansion from the tillering stage most when combined with high N rate, and especially in barley (exp II), but no such effects were found in exp I. Use of a high N fertilizer rate (exps I and II) and green manuring (exp II) also resulted in high post-anthesis LAD. Such modifications enabled higher rates of grain- and head-filling, and in exp I contributed to increased head weight and grain yield. Selection for inherent differences in growth type provided an additional possibility for manipulation of canopy structure and yield formation.     

Effect of Foliar Applications of Glycinebetaine on Stress Tolerance, Growth, and Yield of Spring Cereals and Summer Turnip Rape in Finland

Crop losses caused by environmental stresses might be reduced by applying osmoprotectans to crop canopies. Glycinebetaine is endogenously accumulated by some halophytes under stress conditions and represents such a compound. Glycinebetaine was applied exogenously to barley ( Hordeum vulgare L.), oat ( Avena sativa L.), spring wheat ( Triticum aestwum L.), and summer turnip rape ( Brassica rapa ssp. oleifera DC.) canopies and its optimal concentration was monitored in the greenhouse. In field experiments the response of crop plants to betaine applications was assessed by measuring accumulation of above ground biomass, leaf area index (LAI), leaf chlorophyll, and yield. The optimum betaine concentration producing advantageous effects on growth and crop physiology in turnip rape was close to 0.1 M and for wheat 0.3 M. Such concentrations promoted accumulation of betaine similar to that of halophytes under stress conditions [ca. 200 μmol (g DM)⁻¹]. In the 1993 field experiment peak LAIs were recorded in irrigated wheat and barley treated with 17.5 kg ha⁻¹ betaine applied at 300 1 ha⁻¹. Green leaf area was slightly more persistent in wheat treated twice with 1 kg ha⁻¹ betaine applied at 200 1 ha⁻¹ in 1994, although it was not associated with increased grain yield. Our results indicated that betaine has no actual potential in Finland for the principal grain crops but further studies are needed in stress prone environments to assess the potential of betaine treatments for preventing crop failures.     

Waterlogging Affects Leaf and Tillering Dynamics in Wheat and Barley

The aim of this study was to analyse (i) the crop attributes that determine flowering time (i.e. final leaf number, FLN; and phyllochron, Phy), (ii) the dynamics of tiller appearance and (iii) the synchrony between leaf and tiller appearance in wheat and barley plants exposed to waterlogging. Two experiments were carried out in pots, in which wheat and barley cultivars were exposed to five waterlogging treatments, during different periods throughout the crop cycle, from emergence to maturity. The appearance of leaves and tillers on the main stem was measured twice a week in labelled plants. Waterlogging from emergence to flag leaf appearance significantly delayed time to flowering. The delay was greater when waterlogging occurred at the beginning of tillering, lengthening the period from emergence to flowering 24 % (13–15 days) in barley and 10–15 % (6–10 days) in wheat, as compared to control. Phy was the main attribute explaining the delay in flowering, as FLN was not altered. Waterlogging during the early stages of development reduced tiller appearance rate (TAR) in both species, but this effect was partially counterbalanced by a lengthening of the tillering phase, so the effect on final tiller number at maturity was limited. In conclusion, the exposure of wheat and barley to waterlogging during early stages of development delayed time to flowering and reduce TAR in both species. Waterlogging during more advanced crop stages produced slight effects on tillering dynamics, which would indicate that waterlogging affected structure generation more than mortality.     

烯效唑干拌种对小麦分蘖期间内源激素及糖氮比的影响

为了探明烯效唑干拌种对小麦分蘖期间内源激素及糖氮比的影响,本试验以小麦品种绵阳26为材料,采用间接酶联免疫吸附法和作物生理研究方法对其进行了研究。结果表明：烯效唑处理提高了分蘖节内ZT含量和ZT/IAA、ZT/ABA、IAA/ABA、GA/ABA比值,降低了ABA含量;在分蘖前期降低了IAA和GA含量,分蘖进入两极分化阶段IAA和GA含量升     

Fungal Endophytes Enhance Agronomically Important Traits in Severely Drought‐Stressed Barley

Crops often face severe and damaging local drought events, and in some regions, these episodes are predicted to become more frequent due to climate change. Some micro‐organisms have been shown to improve drought tolerance and improve yield in crop plants. Here, we show that fungal root endophytes isolated from a wild barley species (Hordeum murinum subsp. murinum) induced significant improvements in agronomic traits for a severely drought‐stressed barley cultivar grown in a controlled environment, including number of tillers, grain yield and shoot biomass. Five endophyte strains were tested, and the trait that showed the greatest significant difference in the drought‐stressed plants was the number of tillers, where all of the endophyte treatments induced a greater number of tillers per plant. However, except in one case, the mean dry root weight for all plants was greater in the control plants, indicating preferential allocation of resources to aboveground parts in the endophyte treatments. Results were not consistent across all endophyte treatments, with some endophytes performing much better than others. As these growth studies were conducted using soil‐based compost, the results may translate to the field and suggest that some of these endophytes have potential as barley inoculants in arid growing conditions.     

Einfluß von Monoethanolamin auf den Ertrag von Kulturpflanzen

Effect of monoethanolamine on yield of crops
I. Studies on the effect of monoethanolamine on the grain yield and the nitrogen household in cereal plants (pot experiments)
The effect of monoethanolamine (EA, applied as foliar spray, 10 mg per pot) on grain yield and yield components was investigated in pot experiments with spring barley, winter wheat, and winter rye. Under conditions of a moderate drought stress the applied EA increased the grain yield of spring barley from 5 % to 7 % (significance only at α= 0.05). A stimulating effect of EA on the grain yield of winter wheat and winter rye was also obtained.
The positive influence of EA on the grain yield of spring barley was reproducible under the conditions of a limited water supply in small-scale plot experiments (increase of yield about 9 %).
In case of spring barley and winter rye the increase of the grain yield by EA, applied at growth stage 31 (= DC 31) was connected with a greater number of ear-bearing tillers. The increase of the winter wheat yield resulted from more grains per ear of the tillers.
The enhanced formation of tiller grain mass and total tiller biomass by EA was in correlation with a higher nitrogen import into tillers (r = 0.8⁺). Since an export of N from the main shoots into the tillers was not observed a higher N uptake (≥ 6 %) was calculated from N balances. After a fertilization with ¹⁵N-labelled fertilizers the additional ¹⁵N uptake was 13 % to 20 %.
Possible stress reducing activities caused by EA are discussed.     

Effects of Seeding Rate on Growth Duration and Accumulation and Partitioning of Dry matter in Oats

Crop management influences considerably the three components of grain yield, growth duration, growth rate, and harvest index (HI). Effects of seeding rate on these yield components in oats ( Avena sativa L.) was assessed in field experiments at the Viikki Experimental Farm, University of Helsinki, Finland (60°13'N) in 1991 and 1992. Three Finnish oat genotypes were evaluated; a long-strawed landrace cultivar, a moderately long-strawed modern cultivar, and a semi-dwarf breeding line. The following traits were measured: grain yield, days from sowing to yellow ripeness, number of tillers on main shoot, phytomass, vegetative phytomass, and their growth rates (PGR and VGR, respectively), panicle weight and its filling rate (PFR), HI, leaf area index (LAI), and at intervals, dry-matter accumulation in leaves and straw.
Increases in seeding rate significantly decreased growth duration and PGR of individual plants but increased PGR on a ground area basis. Seeding rate did not, however, affect HI. When seeding rate was increased from 200 seeds m⁻² to 500 seeds m⁻², reductions in vegetative phytomass, panicle weight, VGR, and PFR for individual plants ranged between 20 and 40 %, depending on genotype. At ≥600 seeds m⁻² differences in these components between seeding rates were modest. However, PGR, VGR, and PFR per unit ground area increased with increasing seeding rates up to 600–700 seeds m⁻². Moreover, the higher the seeding rate, the higher the peak LAI (2.7 maximum) and the earlier the canopy closure. Hence, our results showed that a seeding rate of 600–700 seeds m⁻², which resulted in uniculm growth habit, is advantageous in terms of grain yield at high latitudes due to higher biomass accumulation and subsequently greater interception of PAR.     

Can Leaf Chlorophyll Measures at Differing Growth Stages be used as an Indicator of Winter Wheat and Spring Barley Nitrogen Requirements in Eastern Canada?

Plant need-based N management approaches may increase the efficiency of N fertilizer application in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). The leaf chlorophyll concentration estimated through the SPAD-502 meter gives a relative assessment of N status in crop. Field trials were conducted near St John's, Newfoundland, between 1997 and 2000 to describe the relationship between winter wheat and spring barley grain yield, protein content, protein yield and SPAD measurements, as affected by differential stage of crop growth, seeding rate and topdress N fertilizer. Grain yield, protein content, and protein yield of winter wheat and spring barley exhibited linear responses to increasing N topdress application rate. SPAD-502 values were moderately to highly positively correlated with grain yield, protein content, and protein yield as a result of increasing topdress N fertilization, and moderately negatively correlated as a result of increasing seeding rate. It may be difficult to make an N-application rate recommendation based on SPAD measurements, as a critical SPAD value may vary among years, locations, cultivars and soil characters.     

Simulation of growth and development processes of spring wheat in response to CO2 and ozone for different sites and years in Europe using mechanistic crop simulation models

The response of crop growth and yield to CO₂ and ozone is known to depend on climatic conditions and is difficult to quantify due to the complexity of the processes involved. Two modified mechanistic crop simulation models (AFRCWHEAT2-O3 and LINTULCC), which differ in the levels of mechanistic detail, were used to simulate the effects of CO₂ (ambient, ambient ×2) and ozone (ambient, ambient ×1.5) on growth and developmental processes of spring wheat in response to climatic conditions. Simulations were analysed using data from the ESPACE-wheat project in which spring wheat cv. Minaret was grown in open-top chambers at nine sites throughout Europe and for up to 3 years at each site.

Both models closely predicted phenological development and the average measured biomass at maturity. However, intermediate growth variables such as biomass and leaf area index (LAI) at anthesis, seasonal accumulated photosynthetically active radiation intercepted by the crop (ΣIPAR), the average seasonal light use efficiency (LUE) and the light saturated rate of flag leaf photosynthesis (A_sat) were predicted differently and less accurately by the two models. The effect of CO₂ on the final biomass was underestimated by AFRCWHEAT2-O3 due to its poor simulation of the effect of CO₂ on tillering, and LAI.LINTULCC overestimated the response of biomass production to changes in CO₂ level due to an overprediction of the effect of CO₂ on LUE. The measured effect of ozone exposure on final biomass was predicted closely by the two models. The models also simulated the observed interactive effect of CO₂ and ozone on biomass production. However, the effects of ozone on LAI, ΣIPAR and A_sat were simulated differently by the models and less accurately with LINTULCC for the ozone effects on LAI and ΣIPAR. Predictions of the variation between sites and years of growth and development parameters and of their responses to CO₂ and ozone were poor for both AFRCWHEAT2-O3 and LINTULCC. It was concluded that other factors than those considered in the models such as chamber design and soil properties may have affected the growth and development of cv. Minaret. An analysis of the relationships between growth parameters calculated from the simulations supported this conclusion. In order to apply models for global change impact assessment studies, the difficulties in simulating biomass production in response to CO₂ need to be considered. We suggest that the simulation of leaf area dynamics deserves particular attention in this regard.     

Relation Between Pattern of Development of Wheat Seedlings and Growth Rate of Leaves, Tillers and Roots

Relation between pattern of development of wheat seedlings (Triticum aestivum L. Fiori et Paol.) and growth rate of leaves, tillers and roots.
In two glasshouse and two phytotron experiments, the early growth and development of spring wheat and unvernalized autumn wheat in long and short days was observed by frequent assessments of dry weight of shoots and roots and by daily measurements of length and dry weight of individual leaves. In an additional experiment, the pattern of dry matter distribution during germination was studied.
The rate of leaf emergence and appearance was decelerated by short days in spring wheat and by long days in unvernalized autumn wheat.
The growth rate of individual leaves showed a pattern of successive reductions and accelerations, being highly synchronized between leaves and clearly related to the succession in emergence of leaves and tillers.
Growth rates of main shoot and tillers were apparently synchronized, while those of the seminal root system appeared to show an oppositional pattern as compared to the shoot.
It is suggested that variation in the growth rate of existing organs is based on hormone controlled variation in meristematic activity, which is influenced by day length and the state of vernalization of the plant.     

Simulation of wheat growth using the 3D root architecture model SPACSYS: Validation and sensitivity analysis

SPACSYS, a model of C and N cycling in the soil–plant–atmosphere continuum that incorporates a detailed three-dimensional root growth sub-model, was tested for its ability to predict the growth and root length density (RLD) distribution of winter wheat. The root growth sub-model was parameterized using published or unpublished data for wheat and barley, and validated against an independent data-set from field experiments on wheat in the UK published in 1978. The model reproduced the experimental results well, accurately simulating total above-ground (r = 0.98) and root (r = 0.96) biomass. There was a slight tendency to over estimate root biomass before the start of stem extension and the rate of root loss after anthesis, suggesting that the partitioning coefficient for dry matter between shoot and root system overwinter and the rate of root mortality and the root decay constant after anthesis may require some adjustment. Simulations of rooting depth and RLD distribution over the season were also acceptable. Further simulation work investigated the sensitivity of root length and relative distribution in the soil profile to changes in specific root morphological traits. The total length of the root system was sensitive to changes in traits regulating the number of lateral branches a given root order can produce (the inter-branch distance, the maximum length of root and its apical non-branching distance) and the elongation rate of main axes. The distribution of the root system was most sensitive to the maximum elongation rate of main axes and their initial growth trajectory. The model will have applications in guiding the design of root system ideotypes for improved water and nutrient use efficiency and for investigating their effectiveness under a range of soil conditions and crop management regimes.     

Reduced Tillering Spring Wheats for Heavy Textured Soils in a Semi-arid Mediterranean Environment

Low tillering lines of spring wheat ( Triticum aestivum L.), were evaluated for their ability to conform to a high yielding ideotype in a dryland environment with spring drought. The ideotype was based on a concept of saving water as a result of reduced canopy development before anthesis; this should improve moisture supply for grain filling, thus reducing the effect of drought.
Five genotypes were compared under two nitrogen (N) levels, and at similar plant densities, at a site in the drier wheatbelt area of southwestern Australia. The genotypes formed three tillering groups based on the maximum number of culms produced: a free tillering group (G1), which included the standard cultivar Gamenya , with 4.3 culms per plant, an intermediate tillering group (G2) with 3.2 culms per plant, and a low ullenng group (G3) with 2.4 culms per plant.
Leaf area indices (LAI) were strongly affected by N but this was not reflected in total water use and biological yield. However, water was prematurely depleted before anthesis as a result of rapid early leaf development in response to N, and this reduced grain yield. Reduced tillering produced no significant increase in gram yield over the controls; fewer tillers per plant failed to suppress LAI development and water-use before anthesis because of a compensating increase in LAI; this resulted from a greater leaf size in the reduced tillering lines. Hence the low tillering lines did not fully conform to the requirements of the ideotype.
The development of low tillering lines is seen as a significant advance towards the ideotype; with yields comparable to commercial cultivars grown in the region, their performance indicates a potential for substantially higher yields if compensating increases in leaf development can be suppressed.     

Relationship Between Ion Accumulation and Growth in Two Spring Wheat Lines Differing in Salt Tolerance at Different Growth Stages

A salt-tolerant line, S24, of spring wheat was compared with a salt-sensitive line, Yecora Rojo, in sand cultures at four different growth stages, i.e. germination, seedling, tillering and booting, under greenhouse conditions. The NaCl treatments used were 0 or 125 mol m⁻³ in full strength Hoagland's nutrient solution. S24 exceeded Yecora Rojo in biomass or grain yield at the tillering and booting stages, but these lines did not differ at the initial growth stages, i.e. germination and seedling. The growth performance of the two lines at different growth stages was positively related to the pattern of accumulation of cations and anions. The superiority of S24 to Yecora Rojo at the two later growth stages was related to its relatively low accumulation of Na⁺ or Cl⁻ and high accumulation of K⁺ in leaves. The former line also maintained higher leaf K/Na ratios, Ca/Na ratios, K versus Na selectivities and Ca versus Na selectivities than the latter particularly at the tillering and booting stages. Salt tolerance in spring wheat, in this study, is found to be age-dependent. The booting stage has been found as one of the most appropriate growth stages where maximum differentiation in salt-tolerant and salt-sensitive lines occurred. As is evident from previous studies with spring wheat, in the present study there is a positive correlation between partial exclusion of Na⁺ or Cl⁻¹ from the tissues and maintenance of high tissue K/Na and Ca/Na ratios, and K versus Na and Ca versus Na selectivities, and salt tolerance of this crop.     

华北平原免耕冬小麦生长发育特征研究

2004—2006年在河北栾城中国科学院农业生态试验站开展了不同耕作方式下冬小麦生长发育特征及其影响因素的比较研究。冬小麦基本苗数和分蘖率在不同耕作方式间差异显著, 表现为免耕<旋耕<翻耕。免耕处理冬小麦分蘖成穗率高于翻耕和免耕处理, 但基本苗数低, 2004—2005生长季比翻耕和旋耕处理分别低28.9%和29.7%, 2005—2006生长季分别低11.7%和10.0%; 免耕处理冬小麦株高、叶面积指数、地上部干物质积累和产量均低于翻耕和旋耕处理, 其中叶面积指数在2004—2005和2005—2006生长季的最高值分别为2.9和6.0, 产量比翻耕降低30.1%和27.19%、比旋耕降低15.3%和25.20%。免耕可保持耕层较高的土壤水分含量, 总体上高于翻耕和旋耕处理; 免耕处理在冬小麦苗期和返青期表现出明显的“降温效应”, 耕层土壤日均温度低于翻耕和旋耕, 冬小麦出苗和返青较翻耕和旋耕分别晚1~3 d和4~5 d。     

光温要素对水稻群体茎蘖增长动态影响的分析及模拟

为研究水稻茎蘖增长阶段光温要素对茎蘖动态的影响,并验证现有茎蘖动态模拟模型中的光温影响方程,以籼型两系杂交稻陵两优268和两优培九为试验品种,进行了为期2年每年7个播期的大田试验。首先,采用Richards方程对茎蘖观测数据进行拟合,获取茎蘖增长动态的特征参数。然后,分析特征参数与茎蘖增长期内平均光温要素和气候要素的关系,并在此基础上,以光温组合因子为自变量,分别构建2个品种茎蘖增长速率和分蘖率的光温组合影响方程,将获取的方程替换水稻群体茎蘖动态模拟模型中的光温影响方程。最后,验证和比较替换前后模型的模拟结果及与实测茎蘖动态的误差。结果显示,受光温要素的共同作用,平均茎蘖增长速率和最大茎蘖密度均与光温要素显著正相关,表明光温要素不仅影响茎蘖增长速率,也影响实际最大群体茎蘖密度,这在构建的光温组合影响方程中得到了较好的反映。较现有模型,替换后模型在茎蘖增长动态上的模拟误差总体减小,模拟的茎蘖增长速率和最大茎蘖密度与实际吻合较好,但在部分验证数据上仍存在较大误差。然而,本文提出的验证和改进光温影响方程的方法,对了解光温影响机制和完善群体茎蘖动态模拟模型具有一定的参考价值。     

Variation Between Barley Cultivars in Early Response to Weed Competition

An experiment was conducted with three spring barley ( Hordeum vulgare ssp. vulgare L.) cultivars of contrasting competitiveness to identify variations in their early competitive response to weed competition and to study canopy architecture and growth development at the early stages of cultivar growth. The aim was also to investigate whether differences in shoot morphology, growth development and competitive response could explain the differences in competitive ability against weeds. The barley cultivars were grown outdoors in boxes either in monoculture or in a mixture with white mustard ( Sinapis alba L.) as a model weed. The experiment was run until the barley cultivars were in the stem elongation stage. The varieties with strong to medium competitive ability against weeds shortened the time of emergence in the presence of S. alba in contrast to the least competitive cultivar. The results also indicated that spring barley cultivars with strong competitive ability against weeds have an early stem extension as a response to weed competition and a low competitive response. Morphological traits, namely large length of the two first internodes, long main shoot in the tillering stage and a small leaf angle, may be important traits in competition for light.     

杂交中稻根系及地上部性状对结实率的通径分析

以21个籼型杂交中稻组合为材料，用标准化的基因型值进行了根系及地上部植株的21个性状对结实率的通径分析。结果表明：4叶期单株分聚数、分聚盛期单株分聚数、分聚盛期单株干重、分聚盛期发根力、齐穗期LAI、最高苗数和着粒数7个性状对结实率的偏相关系数达到显著或极显著水平，高结实率品种要求分聚力和发根力强，齐穗期LAI高，穗子偏小。     

Leaf Area Duration of Oat at High Latitudes

Contribution of leaf area duration (LAD) to grain yield during the short growing season characteristic of northern latitudes may differ from the marked impact it has at lower latitudes. Three experiments (exps) were carried out at Viikki Experimental Farm, University of Helsinki, Finland (60° 13′N) to compare associations between main shoot and tiller LAD with grain yield, yield components and morpho-physiological traits characterizing plant stand structure. This was done using correlation analysis and principal component analysis (PCA) for data from trials conducted during 1993–1995. Exp I included three N fertilizer rates (80, 120, 160 kg N ha^?1), three seeding rates (250, 500, and 750 seeds m^?2), and tall, moderate, semi-dwarf, and dwarf oat lines. Exp II incorporated two N fertilizer rates (80 and 120 kg ha^?1), three seeding rates (400, 600, and 800 seeds m^?2), and naked and hulled oat lines, and exp III, foliar applications of plant growth regulators [control, chlormequat chloride (CCC), and ethephon], and dwarf, naked, and conventional oat lines. LAD for main shoots and tillers [calculated as ∫ LAI d T, where T is cumulated degree days from seedling emergence to yellow ripening (dd °C)] and 12 morpho-physiological traits were measured. Oat was not able to benefit from high main shoot LAD if drought occurred at grain-fill, but in the absence of severe drought or if it occurred at pre-anthesis, high LAD favoured yield formation. Tiller LAD had a negative impact, if any, on grain yield in cases of an inverse relationship between tiller LAD and yield components on main shoots was recorded. Use of low seeding rates resulted in improved ability of total LAD to contribute to dry-matter production, but was not associated with grain yield. Low seeding rates enhanced formation of high tiller LAD, which was not able to compensate for grain yield reduction caused by fewer main shoots. Foliar application of CCC and ethephon tended to increase the proportion of LAD production by tillers at the expense of grain yield, which can be attributed to lower post-anthesis precipitation. Oat types differed in main shoot and tiller LAD. Disadvantageous characteristics of naked oat, such as low single groat weight, were not associated with insufficient main shoot LAD. High tiller LAD in naked lines and the Minnesota-adapted dwarf line that was not associated with high tiller grain yield in naked lines, in particular, indicates that tiller growth was enhanced at the expense of grain yield production. Application of N fertilizer at various rates did not have any effect on LAD.     

播栽期对机插超级杂交籼稻分蘖成穗的影响及与气象因子的关系

为探讨不同播栽期对机插超级杂交籼稻分蘖成穗的影响,以F优498和宜香优2115两个超级杂交籼稻品种为材料, 设置3月21日(S1)、3月31日(S2)、4月10日(S3)、4月20日(S4)和4月30日(S5) 5个播期,秧龄均为30 d,移栽期依次为4月21日、5月1日、5月11日、5月21日和5月31日,研究其分蘖发生成穗特点及与气象因子的关系。结果表明,不同播栽期水稻产量差异显著,随着播栽期推迟,产量呈降低趋势,早播S1的产量最高、迟播S5的产量最低。不同播栽期处理下水稻主茎对产量的贡献表现为(S1~S4) < S5,一、二次分蘖总和对产量的贡献表现为(S1~S4) > S5,S1优势蘖位为第3~第6叶,而S2~S5优势蘖位为第3~第5叶。随播栽期推迟,分蘖发生和成穗叶位趋于集中,F优498一次分蘖发生在S1~S4以3/0~7/0为主,而在S5以3/0~6/0为主;宜香优2115 在S1以3/0~7/0为主,在S2~S5以3/0~6/0为主。一次分蘖成穗率在S1以3/0~6/0为主,而在S2~S5以3/0~5/0为主;二次分蘖发生和成穗以第3~第4叶为主。气象因子对分蘖发生和成穗的影响为一、二次分蘖发生率与日平均相对湿度呈显著负相关,而与平均气温日较差、积温、日照时数呈显著或极显著正相关;一次分蘖成穗率与分蘖期日平均相对湿度、平均气温呈显著负相关,与分蘖期平均气温日较差、积温、日照时数呈显著正相关,与幼穗分化期日平均相对湿度呈显著负相关,与抽穗开花期日照时数呈显著正相关。综合看来,成都平原地区机插超级杂交籼稻在4月11日前播种5月11日前移栽有利于产量的提高,在4月21日前播种5月21日前移栽有利于稳产,在4月21日以后播种5月21日后移栽产量显著降低。