Analysis of Growth and Yield of Winter and Spring Wheats

In a field experiment to investigate the physiological causesof variation in yield between autumn- and spring-sown wheatand between old and new varieties, the grain yields of the winterwheats were 3-15 per cent, greater than of the spring ones andthe new varieties Cappelle-Desprez and Jufy I yielded 40-70per cent, more than Squarehead's Master and Atle. Nitrogen fertilizerincreased the yields of Cappelle-Desprez and Jufy I more thanof Atle, and decreased the yield of Squarehead's Master by makingit lodge. Until ear emergence the winter varieties had greater leaf-areaindices (L) and dry weights, but smaller net assimilation rates(E), than the spring varieties. Square-head's Master had greaterL but smaller E, and similar dry weight to Cappelle-Desprez.Jufy I had similar E to Atlc, but greater L and dry weight.Nitrogen increased L and dry weight, but decreased E. All thedifferences in E between varieties and nitrogen treatments couldbe explained by the opposite effects on L, that is to say, thedifferences in E were caused by variation in mutual shadingarising from the differences in L and not by changes in leafphysiology. L of winter wheat reached its maximum at the end of May, butL of spring wheat continued to increase until ear emergence.Afterwards Ldecreased more rapidly for winter than for springwheat, so that eventually spring wheat had the greater L. Thesedifferences in the time changes of L partially compensated forthe shorter growth period of spring wheat, and tended to equalizethe grain yield from winter and spring sowings. After ear emergence total dry weight of winter varieties continuedto be greater than of spring ones, but the difference in dryweight of ears was much smaller because ear: shoot dry-weightratio was greater for the spring varieties. Total dry weight,ear dry weight and ear: shoot ratio were all greater in thenew than in the old varieties. Leaf area duration (D) afterear emergence was slightly greater for the winter than for thespring varieties and similar for old and new. The apparent efficiencyof this leaf area in grain production, measured by the grainleaf ratio (ratio of grain dry weight to D), was similar forwinter and spring varieties but greater for new than for old.This suggests that Cappelle-Desprez and Jufy I have higher grainyields because their ears photosynthesize more than do the earsof Squarehead's Master and Atle. Before ear emergence winter varieties had more shoots than springones, and old varieties more than new. After ear emergence therewere only small differences in numbers of ears; percentage survivalwas greater for spring than for winter and for new than forold varieties. Differences in dry weight between varieties were not causedby differences in nitrogen uptake.     

The effect of tiller removal and tiller defoliation on competition between the main shoot and tillers of spring barley

In glasshouse and field experiments the source-sink relations of the main shoot of plants of spring barley were modified by tiller removal and tiller defoliation. Decreasing competition by tiller removal promoted the growth of the residual main shoot and its component parts, and the earlier tillers were removed the greater was the effect. Stem dry weight was increased four-fold in the glasshouse by early tiller removal and was doubled in the field experiment. The grain yield of the main shoot ear was increased by 26 – 30% by tiller removal compared with tillering control plants and this was due to larger grains in all spikelet positions. On the other hand increasing competition by regular tiller defoliation had relatively little effect on the growth and development of the main shoot in the glasshouse study, but in the field the main shoot grain yield was reduced by 10% compared with the control. The main effect of tiller defoliation was on the development of tillers. In the glasshouse tillers survived repeated defoliation, continued to be produced, and the majority produced grain but with fewer and smaller grains per ear than in control plants. Tiller growth was supported by the import of assimilate from the main shoot and this was accompanied by an increase in the photosynthetic rate of the main shoot leaves. In the field all defoliated tillers died within 4 wk. These responses are discussed in terms of the physiological interrelations between the main shoot and tillers.     

Tillering in grain sorghum over a wiide range of population densities: modelling dynamics of tiller fertility

The prediction of tillering is poor or absent in existing sorghum crop models even though fertile tillers contribute significantly to grain yield. The objective of this study was to identify general quantitative relationships underpinning tiller dynamics of sorghum for a broad range of assimilate availabilities. Emergence, phenology, leaf area development and fertility of individual main culms and tillers were quantified weekly in plants grown at one of four plant densities ranging from two to 16 plants m(-2). On any given day, a tiller was considered potentially fertile (a posteriori) if its number of leaves continued to increase thereafter. The dynamics of potentially fertile tiller number per plant varied greatly with plant density, but could generally be described by three determinants, stable across plant densities: tiller emergence rate aligned with leaf ligule appearance rate; cessation of tiller emergence occurred at a stable leaf area index; and rate of decrease in potentially fertile tillers was linearly related to the ratio of realized to potential leaf area growth. Realized leaf area growth is the measured increase in leaf area, whereas potential leaf area growth is the estimated increase in leaf area if all potentially fertile tillers were to continue to develop. Procedures to predict this ratio, by estimating realized leaf area per plant from intercepted radiation and potential leaf area per plant from the number and type of developing axes, are presented. While it is suitable for modelling tiller dynamics in grain sorghum, this general framework needs to be validated by testing it in different environments and for other cultivars.     

草地早熟禾种子产量构成因素的品种差异

对草地早熟禾 2 8个品种种子产量及性状进行了研究 .结果表明 ,2 8个品种间种子产量存在极显著差异 (P <0 .0 1) ,最高的品种为Balin和Monoply ,其产量达 6 4 3.4～ 6 5 0 .2kg·hm-2 ,为最低品种Elysee(90 .1kg·hm-2 )的 7.1倍 .生产性状相关分析表明 ,生殖枝数 /株、生殖枝高、花序长及小穗数 /生殖枝 4个性状为影响早熟禾种子产量的主要因素 .依据对种子产量及上述 4个性状测定值的聚类分析 ,可将 2 8个品种的种子生产性能分为极强、很强、强、中等、差和极差 6个类群 ,其中Monoply等 6品种为极强类群 ;Baronie、Balin和Sydsport、Entopper分别为很强和强类群 ;Nublue等 12品种为中等类群 ;Broadway等 4品种和Ram1、Elysee分别为差和极差类群     

Varietal response in wheat to water supply in the field, and male sterility caused by a period of drought in a glasshouse experiment

Field experiments in 1961 and 1962 with four winter wheat varieties (Professeur Marchal, Cappelle-Desprez, Hybrid 46 and Holdfast) compared three water regimes: irrigation to prevent the soil water deficit exceeding 2 in.; shielding from rain; and normal rainfall. The experiments were done on soils selected for their liability to drought. Grain yield was decreased by water deficit; the effects differed between varieties, but the varietal differences were not consistent in the 2 years. In glasshouse experiments, plants of Cappell-Desprez were subjected to drought for 3–4 days during ear development and subsequently watered normally. When this treatment preceded pollen meiosis by a few days many of the lower florets of each spikelet were male-sterile but female-fertile. Also there was often proliferation, within the spikelet, of normally fertile florets above the male-sterile ones, showing that the number of florets formed may increase until a late stage in ear development. The results of the field experiment suggested that grain yield was restricted by the capacity of the grains as sinks for photosynthates. If so, a genetic improvement in grain yield could be obtained by breeding for an increase in number of florets per spikelet.     

Assimilation of 14CO2, Assimilate Translocation and Grain Yield in Three Primitive Nepalese Varieties and a European Cultivar (Senta) of Six-row Barley (Hordeum vulgare L.)

Three primitive varieties of six-row barley from Nepal withdifferent degrees of awn development were compared with a bredEuropean cultivar, Senta, under glasshouse conditions, fromanthesis onwards. Apart from the flag leaf the last three mainshoot leaves of the Nepalese varieties were smaller than thoseof Senta, and the lower leaves did not become senescent duringthe first 3 weeks of grain filling. In all varieties the penultimateleaf was the major assimilatory organ but in Senta the relativecontribution of the awns increased with time as the leaves senescedand fixed almost half of the total ¹⁴C assimilated by the shoot.Whereas the supply of assimilate to the ear increased with timein Senta, the reverse was found for the Nepalese varieties andoverall a smaller proportion of assimilate was supplied to theear in these varieties. The grain yield of the main shoot earof the two Nepalese varieties studied in detail was one-thirdof that of Senta; there were only approximately half the numberof grains in each median and lateral row of the ear and thegrains were smaller. There was no correlation between the degreeof awn development or the pattern of awn arrangement withinthe ear and the size of individual grains. The total biomassof the Nepalese varieties was much lower than that of Sentabut there were no differences in the harvest index or in tillerproduction. However, the Nepalese varieties, in contrast toSenta, had a mean grain yield per tiller comparable to thatof their main shoot and thus it appears that selection by plantbreeding may have increased the dominance of the main shoot. Hordeum vulgare L., barley, primitive barley varieties, carbon dioxide assimilation, assimilate translocation, grain filling     

Down-regulation of Glucan, Water-Dikinase activity in wheat endosperm increases vegetative biomass and yield

A novel mechanism for increasing vegetative biomass and grain yield has been identified in wheat (Triticum aestivum). RNAi-mediated down-regulation of Glucan, Water-Dikinase (GWD), the primary enzyme required for starch phosphorylation, under the control of an endosperm-specific promoter, resulted in a decrease in starch phosphate content and an increase in grain size. Unexpectedly, consistent increases in vegetative biomass and grain yield were observed in subsequent generations. In lines where GWD expression was decreased, germination rate was slightly reduced. However, significant increases in vegetative growth from the two leaf stage were observed. In glasshouse pot trials, down-regulation of GWD led to a 29% increase in grain yield while in glasshouse tub trials simulating field row spacing and canopy development, GWD down-regulation resulted in a grain yield increase of 26%. The enhanced yield resulted from a combination of increases in seed weight, tiller number, spikelets per head and seed number per spike. In field trials, all vegetative phenotypes were reproduced with the exception of increased tiller number. The expression of the transgene and suppression of endogenous GWD RNA levels were demonstrated to be grain specific. In addition to the direct effects of GWD down-regulation, an increased level of α-amylase activity was present in the aleurone layer during grain maturation. These findings provide a potentially important novel mechanism to increase biomass and grain yield in crop improvement programmes.     

Intergenotypic competition and shoot production in wheat plants

In field experiments, the competition among plants of two distinct wheat genotypes in binary mixtures, and among three genotypes being grown in adjacent rows was investigated. The competition greatly affected the over-ground dry weight, weight of stem and grain per plant. This effect was undercompensatory, the depression in poor competitor was higher than the enhancement of strong competitor for all these characteristics. From final components of grain yield per plant, the number of fertile stems and number of grains per ear were more affected than weight per grain. More expressively than weight of grain on the main-stem ear, the weight of grain per average secondary ear-bearing stem was affected by competition in binary mixture. The enhancement in standard height—a strongly competitive genotype— reached in binary mixture about 10% for this last characteristic in comparison with the value from the pure stand. Some morphological characteristics of plants being in relation with competition for grain yield per plant are discussed in these experiments.     

Physiological Causes of Differences in Grain Yield between Varieties of Barley

In a field experiment on barley at Rothamsted with the highmean yield of 49 cwt. of grain per acre, the varieties Proctorand Herta produced 10—15 per cent, more grain than Plumage-Archeron plots that received no nitrogenous fertilizer. When nitrogenwas applied the difference was increased to about 30 per cent.,because the higher nitrogen supply caused the Plumage-Archercrop to lodge and did not increase its yield, while Proctorand Herta remained standing. The three varieties did not differ in leaf-area index nor innet assimilation rate before ear emergence, so that all hadthe same total dry weight. After ear emergence, the leaf-areaindices of Proctor and Plumage-Archer were nearly equal, butthat of Herta was smaller. Assuming that the photosyntheticefficiency of the leaves continued to be the same in all varieties,the higher grain yields of Proctor and Herta cannot be attributedto greater production of dry matter by the leaves, either beforeor after ear emergence. A pot experiment on plants with shadedears confirmed that the dry matter contributed to grain yieldby unit leaf area was nearly equal in all the varieties. The higher grain yield of Proctor and Herta than of Plumage-Archermust therefore have come from additional photosynthesis in partsof the plant other than the leaves, i.e. in the ears themselves.An attempt to demonstrate this directly in a pot experiment,by comparing the grain yields of plants with shaded or withunshaded ears, was unsuccessful because the varieties behaveddifferently in pots; Proctor and Herta produced only about 6per cent, more grain yield than Plumage-Archer, and though thedecrease in grain yield by shading the ears was slightly greaterfor Proctor and Herta, the differences were not significant. The sum of ear sizes (estimated from length and breadth measurements)per m.1 in the field experiment was greater for Proctor andHerta than for Plumage-Archer. Also the distribution of drymatter between developing ears and shoots apparently differedwith variety, so that at ear emergence the dry weight of earsper m.² was greater in the two higher yielding varieties. Theincreased amount of photosynthetic tissue in the ears of Proctorand Herta, as measured by size or weight, may not wholly explaintheir greater dry-matter production; ears of Herta may alsohave a higher photosynthetic efficiency. No differences in nutrient uptake that could account for thevarietal differences in grain yield were found. Plumage-Archerabsorbed more potassium, and Herta less phosphorus than theother varieties. About a quarter of the final content of nitrogen,and a third of the phosphorus, was absorbed after ear emergence,but the potassium content was nearly maximal at ear emergenceand later decreased. The pot experiment showed that, on the average of all varieties,26 per cent. of the dry matter in the grain at harvest originatedfrom photosynthesis in the ears, including 10 per cent, fromthe awns; 59 per cent, came from photosynthesis in the flag-leaflamina and sheath and peduncle, and 15 per cent, from partsof the shoot below the flag leaf.     

Tillering in grain sorghum over a wide range of population densities: identification of a common hierarchy for tiller emergence,leaf area development and fertility

Most studies of tiller development have not related the physiological and morphological features of each culm to its subsequent fertility. This introduces problems when trying to account for the effects of tillering on yield in crop models. The objective of this study was to detect the most likely early determinants of tiller fertility in sorghum by identifying hierarchies for emergence, fertility and grain number of tillers over a wide range of assimilate availabilities. Emergence, phenology, leaf area development and dry weight partitioning were quantified weekly for individual tillers and main culms of tillering and uniculm plants grown at one of four densities, from two to 16 plants m(-2). For a given plant in any given density, the same tiller hierarchy applied for emergence of tillers, fertility of the emerged tillers and their subsequent grain number. These results were observed over a range of tiller fertility rates (from 7 to 91%), fertile tiller number per plant at maturity (from 0.2 to 4.7), and tiller contribution to grain yield (from 5 to 78 %). Tiller emergence was most probably related to assimilate supply and light quality. Development, fertility and contribution to yield of a specific tiller were highly dependent on growing conditions at the time of tiller emergence, particularly via early leaf area development of the tiller, which affected its subsequent leaf area accumulation. Assimilate availability in the main culm at the time of tiller emergence was the most likely early determinant of subsequent tiller fertility in this study.     

An investigation into the relations between some growth parameters and yield of barley

Twenty-five field experiments on barley were done at four sites from 1970 to 1975, with an additional site in 1975, comparing five rates of nitrogen application. The crops were sampled at c. 14-day intervals from about the four-leaf stage to maturity to follow changes with time in the dry weights of the constituent plant parts and to measure fertile tiller number, grain number per ear and grain weight. Some data have been selected from this body of information and regression analysis has been used to assess the possible importance of pre- and post-anthesis growth in determining the yield of barley. Ear emergence was taken as an approximate indicator of anthesis. Yield was closely related (r=+0–96) and almost equal to the amount of dry matter accumulated before ear emergence for twenty-one of the experiments, with a regression coefficient of 0–95. In two of the remaining experiments the regression coefficient was greater, 1–14; and smaller in the other two, o-8i. Plant population is also shown to affect the regression coefficient. Despite these anomalies grain yield was more closely related to plant dry weight at ear emergence than to the increase in weight after ear emergence (r =+0–79). The increase in plant dry weight after ear emergence was frequently less than the yield of grain, suggesting that the plant can compensate for inadequate photosynthesis during grain filling. The result of this compensation is a reduction in straw dry weight. This implies that previously assimilated dry matter is transported to the grain, or that respiratory losses from the straw are not replaced by current photosynthesis. These observations suggest that yield may be limited by sink capacity rather than by photosynthesis after ear emergence. The main component of sink capacity, grain number per m² was closely related to yield (r =+0–95) and is known to be determined at or before anthesis. Grain size was shown to be related to grain number per ear (r= 4- 0–99), suggesting that grain size is also, at least partially, determined at ear emergence. Therefore, all the yield components are determined, wholly or partly before ear emergence.     

EFFECTS OF PREVIOUS WHEAT CROPS, SEED-RATE AND NITROGEN ON EYESPOT, TAKE-ALL, WEEDS AND YIELDS OF TWO VARIETIES OF WINTER WHEAT: FIELD EXPERIMENT 1954-56

In a replicated field experiment mean yields of wheat from plots that, in the preceding 2 years, had carried oats, beans or potatoes were 39.2 and 42.6 cwt. per acre in 1954 for Holdfast and Cappelle, respectively; 42.8 and 55.8 in 1955 and 34.9 and 49.6 in 1956. Previous wheat crops had more effect than any other treatment in increasing the incidence of eyespot, take-all and weeds and in decreasing the number of ears per unit area and the yield of grain. In 1956 on plots carrying the first, second and third successive wheat crops the percentages of straws with eyespot were respectively 12, 54 and 42 and with take-all 0.1, 1 and 16. Cappelle was less severely infected by eyespot than Holdfast. The second and third successive wheat crops yielded an average of 23.3 cwt./acre less than the first wheat crop. Cappelle consistently yielded more than Holdfast, the mean difference being 13.8 cwt./acre after potatoes but only 3.8 cwt./acre after two wheat crops. The higher seed-rate gave an average increase in grain yield of 3.3 cwt./acre; but where eyespot and take-all were both severe the lower seed-rate yielded as much total and more dressed grain than the higher. Wheat given a spring top dressing of 6 cwt./acre Nitro-Chalk yielded an average of 4 cwt./acre more grain than wheat given 3 cwt./acre.     

Effect of Defoliation During the Early Vegetative Phase and at Silking on Growth of Maize (Zea mays L.)

Two experiments were conducted in the glasshouse and in thefield to evaluate the effect of leaf loss on development, drymatter accumulation and yield of maize. In the glasshouse, defoliationtreatments were imposed on maize after 3 weeks of planting.Removing 2 or 3 leaves every 2 weeks affected plant height,days to tassel, root and shoot yield. The plant diameter androot:shoot ratio were not affected by defoliation. In the field experiment, six defoliation treatments were imposed7 days after 50 per cent silking. Defoliation of all leaveswas the most severe treatment on cob d. wt, dry matter accumulationin grains, weight of 100 test grains and yield. The effect ofremoving all leaves above the ear was not significantly differentfrom that of removing all leaves below the ear. The effect ofremoving half of the leaves above the ear was not differentfrom the control. Zea mays, vegetative growth, dry matter accumulation, yield, defoliation     

A system for studying the effects of naturally-occurring subzero temperatures on winter barley

Thermostatically-controlled, electrical soil heating cables were used to examine the effects of subzero temperatures on winter barley growing in plots outdoors. Plants in plots without heating cables were exposed to naturally-occurring subzero temperatures (unheated), while those in corresponding plots with the cables (heated) were protected from such temperatures. Measurements of soil, plant and air temperatures in heated and unheated plots showed that the system can, at least with the temperatures encountered during the measurement periods, prevent plant temperature from falling below the temperature set on the thermostat. A field experiment involving different cultivars and sowing dates showed that subzero temperatures experienced did not significantly affect individual plant grain yield or the number of fertile ears produced per plant. However, small, but statistically significant, effects of naturally-occurring subzero temperatures were found in relation to the number of grains per ear, thousand grain weight and harvest index. The nature of these effects varied, and were dependent upon cultivar and/or sowing date. Subzero temperatures were also responsible for reducing the numbers of established plants in late-sown plots through soil heaving. Possible uses of the soil heating cable system for temperature-related studies in the Gramineae are discussed.     

The physiological response of winter wheat to reductions in plant density

The effects of reducing the plant density of winter wheat (cv. Haven) on canopy formation, radiation absorption and dry matter production and partitioning were investigated in field experiments in 1996/97 and 1997/98. Crop densities established ranged from 19 to 338 plants m^?2. Grain yield was maintained with large reductions in plant density. At low plant densities the relative growth rate of the crop increased allowing a maintenance of crop dry matter production. An 18 fold reduction in plant density led only to a six fold reduction in green area index at the beginning of stem extension and by anthesis the difference was less than two fold. Crops grown at low plant densities increased green area per plant through increased duration of tiller production, green area per shoot and shoot survival. Main stem leaf number, phyllochron and tiller production rate were not significantly affected by plant density. Radiation use efficiency was greater at the low plant densities. We propose that better radiation distribution through the canopy and increased canopy nitrogen ratio were the causative mechanisms for this increase in RUE. As a result of increased green area per shoot and a decrease in ear production, more radiation was absorbed per shoot at the low plant densities, allowing an increase in grain number per ear from 32 to 48.     

Effects of alien cytoplasmic variation on carbon assimilation and productivity in wheat

In glasshouse studies of four alloplasmic wheat series, phenotypic characters were least affected when the recipient parent cytoplasm was replaced by donor cytoplasm of the S or D plasmatype. In the T. aestivum cv. 'Selkirk' series, cytoplasm substitution did not affect Pmax per unit leaf area, although the flag leaf area (and photosynthetic rate per leaf) of each alloplasmic line was greater than that of euplasmic 'Selkirk'. In field trials, all the D plasmatype alloplasmics tested produced more ears m^-2 than did euplasmic 'Selkirk'. The increased tiller number and leaf area of alloplasmic lines resulted in greater canopy light interception than euplasmic 'Selkirk' early in the season. This characteristic was associated with reduced weed populations under crops of alloplasmic 'Selkirk' lines grown under low-, but not high-input, agronomic regimes, with Ae. cylindrica- and Ae. ventricosa-'Selkirk' significantly outyielding alloplasmic 'Selkirk' under low-input conditions. The F2 populations from crosses between European wheat varieties and 'Selkirk' lines exhibited higher standard deviations for grain yield for alloplasmic than for euplasmic 'Selkirk', suggesting potential for selecting heterotic nuclear-cytoplasmic combinations with alien cytoplasms.     

干旱对东北春玉米生长发育和产量的影响

选取玉米品种丹玉39为供试材料,利用大型农田水分控制试验场,采用大田池栽方式,在玉米三叶-拔节期、拔节-吐丝期、吐丝-乳熟期分别开展中度干旱胁迫及复水控制对比试验,分析3个关键生育时期干旱胁迫对春玉米生长发育和产量的影响.结果表明：与水分适宜对照（CK）相比,三叶-拔节期遭受干旱胁迫后,全生育期推迟13 d,至拔节普遍期,株高偏低29.8%,叶面积偏小41.2%,复水后,株高和产量得到较大程度恢复,果穗性状和最终产量差异不大;拔节-吐丝期遭受干旱胁迫后,全生育期缩短7 d,至吐丝普遍期,株高偏低18.6%,叶面积偏小14.1%,果穗长、穗粒数、果穗干质量、穗粒质量分别下降6.9%、19.1%、28.1%和29.4%,空秆率增加13.3%;吐丝-乳熟期遭受干旱胁迫后,全生育期缩短15 d,生长至乳熟普遍期,株高偏低2.3%,叶面积偏小37.3%,果穗长、穗粒数、果穗干质量、穗粒质量分别下降9.2%、24.1%、30.8%和27.9%,空秆率增加24.5%.拔节-吐丝期、吐丝-乳熟期干旱胁迫处理并复水后,玉米株高恢复不明显,产量降幅显著.     

Grain yield and quality of wheat as affected by chlormequat (2-chloroethyl-trimethyl ammonium chloride)

Three field experiments studying the effect of chlormequat (CCC) on the grain yield of spring wheat and the quality of the grain for baking purposes were made. In the first, CCC applied as a spray during the stage of rapid internode elongation proved more successful than application as a mixture with superphosphate drilled with the seed at sowing. Both methods prevented lodging and the depression of yield which occurred in the control plots. In the other two experiments the sole method of CCC application was by spraying.
In all three experiments CCC-treated plots had more ears per unit area and grains per ear than control plots; the one exception being at the lowest plant density derived from a seeding rate of 24 kg/ha. CCC helped prevent weather damage to the grain and as a result baking performance of the flour from treated plots was superior to that from the untreated plots.     

High productivity of wheat intercropped with maize is associated with plant architectural responses

Mixed cultivation of crops often results in increased production per unit land area, but the underlying mechanisms are poorly understood. Plants in intercrops grow differently from plants in single crops; however, no study has shown the association between plant plastic responses and the yield advantage. Here, we assessed the productivity of wheat–maize intercropping as compared to sole wheat and sole maize, and the associated differences in wheat shoot and leaf traits. In two field experiments, intercrop wheat and maize were both grown in alternating strips consisting of six rows of wheat and two rows of maize. The traits of wheat plants in border rows of the strips were compared to the traits of plants in the inner rows as well as those in sole wheat. Leaf development, chlorophyll concentration and azimuth, as well as the final leaf and ear sizes, tiller dynamics of wheat and yield components of both crops were determined. The relative densities of wheat and maize in the intercrop were 0.33 and 0.67, respectively, but the corresponding relative yields compared to the respective monocultures were 0.46 for wheat and 0.77 for maize. Compared to wheat plants in the inner rows of the intercrop strips as well as in the monoculture, border‐row wheat plants in the intercrop strips had (a) more tillers owing to increased tiller production and survival, and thus more ears, (b) larger top leaves on the main stem and tillers, (c) higher chlorophyll concentration in leaves, (d) greater number of kernels per ear and (e) smaller thousand‐grain weight. Grain yield per metre row length of border‐row wheat was 141% higher than the sole wheat, and was 176% higher than the inner‐row wheat. The results demonstrate the importance of plasticity in architectural traits for yield advantage in multispecies cropping systems.     

Some effects of barley yellow dwarf virus on spring and winter cereals in glasshouse trials

The tolerance of spring and winter varieties of wheat, oats and barley to infection by barley yellow dwarf virus (BYDV) was examined in glasshouse tests. Severely affected plants were stunted and grain yields were considerably decreased because of decreases in both ear number and numbers and sizes of grains. Winter barley varieties were very susceptible and many were killed by BYDV infection. The winter wheat varieties were more widely tolerant than those of oats and barley. Individual seedling symptoms, although correlated with reductions in yield, could not be relied upon for accurate classification of all varieties in order of their susceptibility to infection. Symptoms of seedling infection incorporated into an index of infection permit estimates to be made o eventual decreases in yield by applying the formula DY = 1.4 × (SH+LA+LL)+18. Thus decrease in grain yield (DY) can be related to decreases in height (SH) and leaf length (LL) and increases in leaf area discoloured (LA) in seedling plants infected with BYDV.