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Effects of seven factors on the growth and yield of winter barley grown as a third consecutive take-all susceptible crop and of growing the barley after oats or a fallow
Abstract
In experiments at Rothamsted in 1984–86, seven factors, each at two levels, were tested in factorial combination on winter barley (cv. Panda) grown as a third take-all susceptible crop. The factors were seed rate, a growth regulator prior to stem extension, amounts of N in spring, ‘winter’ nitrogen, an autumn insecticide, a fungicide applied to the seed (‘Baytan’) and a programme of fungicide sprays in spring and summer. Sowing 50% more seeds than normal increased the number of ears/unit area but had no effect on mean grain yield because grains were smaller. There were, however, significant, but unexplained, interactions between seed rate and the fungicide ‘Baytan’ applied to the seed. A growth regulator applied prior to stem extension had little effect on crop growth and no significant effect on grain yield. If sufficient N was applied in April there was little benefit from applying ‘winter’ N (30 kg/ha in November and again in February/March) except in 1985 when the amount of NO 3 -N in the soil, measured in the previous October, was lowest. Insecticide sprays applied in autumn to control the aphid vectors of barley yellow dwarf virus (BYDV) had no significant effect on grain yield but infectivity indices were below the threshold needed for treatment in each year. On average, ‘Baytan’ applied to the seed increased grain yield by 0·28 t/ha and this was associated with decreases in the severity of take-all. Over the three years, programmes of fungicide sprays, applied during spring and summer, increased grain yield by 0·92 t/ha but the mean response was largest where most N was applied.
The experiments also allowed the importance of interactions between different agronomic factors to be examined. A combined analysis of grain yields for all three years (based on 192 plot values) showed that only six 2- or 3-factor interactions, out of the 73 estimated, were significant ( P < 0·05). Two of these interactions reflected variable responses to ‘winter’ N and fungicide sprays in the three years and three of the remaining four involved ‘Baytan’.
Additional plots of barley grown after oats had little take-all and yielded 1·14 t/ha more grain than similarly treated plots grown after barley. These responses were obtained despite evidence that oat residues had adverse effects on the growth of barley seedlings. Additional plots of barley grown after a bare fallow also had little take-all and gave even larger total yields (grain plus straw) than did barley after oats but the mean yield of grain was less than after oats because more of the dry matter after a fallow was straw. In 1984, when take-all was relatively slight, plots after a fallow gave even less grain than plots after barley (−0·77 t/ha) despite producing 2·12 t/ha more dry matter in grain plus straw.
... In general, yield losses of barley due to an unfavourable cropping history were smaller than in wheat, ranging between 7% and 16% (Pommer & Baumer 1982;Steinbrenner & Obenauf 1986;Jenkyn et al. 1992). However, Buss and Zoschke (1984) reported a yield decline of barley grown in monoculture of 44% compared to barley following potatoes, due to a reduction in all yield components. ...
... Archives of Agronomy and Soil Science 13 14 K. Sieling and O. Christen Prew et al. 1986;McEwen et al. 1990;Jenkyn et al. 1992;Christen 1998;Sieling et al. 2005;Kirkegaard et al. 2008). Changes in weed infestation were not observed and can be excluded as reason for the crop rotation effects. ...
Economic conditions are forcing farmers to grow crops with high revenue leading to cereal dominated crop rotations with increasing risk due to unfavourable preceding crops or preceding crop combinations. Based on a long-term field trial (1988-2001) with 15 different rotations including winter oilseed rape (OSR), winter wheat, winter barley, spring peas and spring oats the effects of different preceding crops, pre-preceding crops and crop rotations on the grain yield of mainly OSR, winter wheat and winter barley were quantified. In the subsequent 2 years (2001/02 and 2002/02), winter wheat was grown on all plots in order to test the residual effects of the former crops (as preceding crops in 2002 and as pre-preceding crops in 2003) and crop rotations on growth, grain yield, and yield components.
... In general, the seed yield of oilseed rape increased with the length of the break between two oil-seed rape crops. Therefore, oilseed rape shows a similar yield response to different preceding crops and cropping history as cereals, of approximately 10% of the grain yield (see, e.g., Prew et al., 1986;McEwen et al., 1989;Christen et al.. 1992;Jenkyn et al., 1993;Christen and Sieling, 1993). The results reported for oil-seed rape support findings reported by Moller and Makowski (1977) as well as George et al. (1985). ...
Information about the effect of the preceding crop or crop combination on the seed yield of oil-seed rape is extremely scarce. Experiments were carried out in northwest Germany to investigate the effect of different preceding crops on the growth, seed yield and yield components of oil-seed rape. The two directly preceding crops, wheat and oil-seed rape, had only a negligible and non-significant effect on the seed yield of the following oil-seed rape crop. Oil-seed rape grown after wheat had more pods per plant, due to an increase in the number of pods on the higher category branches. In contrast, the seed yield and yield components were more affected by the cropping sequence, i.e. the crops 2 years before. Averaged over two experimental years, the greatest yields were observed in oil-seed rape following the sequence peas-wheat (694 g m−2), whereas the smallest seed yield occurred after 2 years of oil-seed rape cropping (371 g m−2). The differences in the seed yield were again associated with more pods per plant, which compensated for the lower number of plants m−2, whereas the number of seeds per pod and the mean seed weight were almost unaffected by the previous cropping. It was not possible to relate the described differences to the crop development, since differences in the biomass caused by the previous cropping were only significant at maturity. Oil-seed rape grown after 2 years of oil-seed rape had the highest ratings of stem canker (Leptosphaeria maculans) as well as verticillium wilt (Verticillium dahliae). But the general level of the diseases was low, and therefore other causes for the effects described must be considered.
Physiology describes the operation of a plant at the biochemical, cell, tissue, organ and whole plant levels, recognizing that all of these are under the control of the plant genome. In the case of crop plants we are interested in how the combined operation of all plant’s functions leads to the production of the harvestable component which, in cereal crops, is generally grain. Broadly speaking, the most important of the physiological activities in a crop plant with regard to yield are dry matter production, nutrient uptake, plant component partitioning and the processes of development (especially grain filling and the other aspects of yield component development). The developmental processes occur sequentially in time and involve progressive shifts in physiology. As barley (Hordeum vulgare L.) is a feed grain and a major source of malting grain for beer and spirits, aspects of physiology that affect the amount of grain produced and its quality (the amount of energy and protein) are of special interest.
The effect of different crop rotations on the grain yield and yield formation of wheat, barley and rapeseed was investigated in the Hohenschulen rotation experiment during the years 1988 to 2000. Additionally the yield stability of winter wheat following different preceding crops was estimated. The grain yields were mainly affected by the direct preceding crops, whereas the influence of the entire crop rotation on the yields was smaller. Under current intensive practice husbandry the yield difference of the three crops ranged between 9% (barley) and 11% (rapeseed). If the rotation was taken into consideration, the differences in grain yield increase to 18% in rapeseed, 11% in barley and 13% in wheat. Wheat grown after wheat showed a smaller yield stability compared with wheat after wheat. The yield reduction after an unfavourable preceding crop in wheat was mainly due to a reduced number of ears per m2 and a smaller thousand grain weight. The number of grains per ears showed a compensational response. The yield differences of rapeseed were caused by a decrease in the thousand seed weight and the number of seeds per m2.
The effect of a comprehensive (three-spray) fungicide programme on yield, specific weight (SW), 1000-grain weight (TGW), nutritive value and yield of both winter and spring oat grains was investigated over a 3-year period (1989–91). With winter oats, four cultivars (Aintree, Image or Pennal, Solva and Kynon), were tested at each of three sites (Gwent, Hereford and Kent). Similarly for spring oats, four cultivars (Dula, Keeper, Rollo and Rhiannon) were tested at each of three sites (Cornwall, North Yorkshire and Wales).
On winter oats, fungicide treatment produced a significant increase ( P <0·05) in grain yield, but did not on spring oats. Fungicide treatment produced no significant effect on SW, TGW or nutritive value of the winter or spring oats. With winter oats, but not with spring oats, fungicide treatment produced a significant increase ( P <0·05) in the yield of digestible (DE) and metabolizable (ME) energy for pigs and ruminants respectively.
The naked oats, Kynon and Rhiannon, had a significantly lower yield, higher SW and lower TGW than the other conventional cultivars ( P <0·05). Their oil, fatty acid, protein, DE and ME contents were also significantly higher than the other cultivars ( P <0·05). Nevertheless, the yield of protein, DE and ME tended to be less from naked oats than from some of the other cultivars tested.
On winter oats, TGW, protein content and protein yield, dry matter (DM) and fatty acid content and on spring oats, yield, TGW, ME yield, DM, oil, fatty acid, protein, DE and ME all varied between years. With winter oats, oil content and energy values were negatively correlated with yield and positively correlated with SW. With spring oats, DE and ME were positively correlated with SW.
It was concluded that, on winter oats, fungicide treatment was worthwhile in terms of grain yield, but this was not the case for spring oats. Also with winter oats, but not spring oats, fungicides gave useful increases in the yield of energy. The naked oats, Kynon and Rhiannon, had a distinct advantage in terms of nutritive value, but their low yield compared with the conventional cultivars tended to negate this benefit.
Reliable estimations of the yield response of winter barley to different preceding crops are necessary for the design of crop rotations.
The grain yield and yield components of winter barley (cv. Tapir ) following either rapeseed, oats, wheat or barley were determined in five years of field experiments on a sandy loam (Luvisol) at the Hohenschulen experimental station near Kiel, Germany, F.R. The growth, development and incidence of take‐all ( Gaeumannomyces graminis var. tritici ) was measured in a total of three years. On average over the five years barley grown after oats yielded 0.8 t per ha (11 %) more than barley following wheat which was mainly due to a higher number of ears per m ² . Barley following either oats or rapeseed produced a higher dry weight and a larger number of tillers per m ² compared with barley grown after wheat or barley. This effect was already‐present at the sampling date before winter. Take‐all ratings were constantly higher in barley following a susceptible crop, but only reached a severe level late in the season and therefore could not explain the observed differences in growth, development and subsequently grain yield. Since no other pathogens affected the development other non‐pathogenic causes must be considered as main causes for the described observations and yield differences.
Winter barley which received a range of nitrogen rates, was grown at Rothamsted as a test crop after winter oats, winter barley, winter beans, oilseed rape or potatoes, to compare the effects of previous crop on growth and N uptake. In the autumn following the first year crops, the largest amount of residual inorganic N found in the soil was after potatoes, the smallest after oats. Throughout the second season the heaviest crops of barley, which also contained the most N, were after potatoes, and the lightest were after barley. To produce grain with a N concentration of less than 1.8% N (w/w, dry wt), acceptable for malting, it was found that not more than 75 kg N ha−1 after barley and 125 kg N ha−1 after oats, 100 kg N ha−1 after beans and 50 kg N ha−1 after rape or potatoes could be applied. The results demonstrated that barley of acceptable quality for malting can be grown after a break crop, providing that the rate of N fertiliser is suitably adjusted to take account of the residual fertility, but the results do not suggest that residual soil N affects the grain N concentration differently to N applied as fertiliser early in the season.
Relationships between take-all intensity and grain yield and quality were determined in field experiments on cereal crops using regression analyses, usually based on single-point disease assessments made during anthesis or grain-filling. Different amounts of take-all were achieved by different methods of applying inoculum artificially (to wheat only) or by using different cropping sequences (in wheat, triticale or barley) or sowing dates (wheat only) in crops with natural inoculum. Regressions of yield or thousand-grain weight on take-all intensity during grain filling were similar to those on accumulated disease (area under the disease progress curve) when these were compared in one of the wheat experiments. Regressions of yield on take-all intensity were more often significant in wheat than in the less susceptible crops, triticale and barley, even when a wide range of disease intensities was present in the latter crops. The regressions usually had most significance when there were plots in the severe disease category. Thousand-grain weight and hectolitre weight usually responded similarly to total grain yield. Decreased yield was often accompanied by a significant increase in the percentage of small grains. When severe take-all was present in wheat, regressions showed that nitrogen uptake was usually impaired. This was sometimes accompanied, however, by increased percentage nitrogen in the grain as a consequence of smaller grain size with decreased endosperm. Significant effects of take-all, both positive and negative, on Hagberg falling number in wheat sometimes occurred. Significant regressions of yield on take-all assessed earlier than usual, ie during booting rather than grain-filling in wheat and triticale and during anthesis/grain-filling rather than ripening in barley, had steeper slopes. This is consistent with observations that severe disease that develops early can be particularly damaging, whilst the crops, especially barley, can later express tolerance by producing additional, healthy roots. The regression parameters, including maximum potential yield (y-axis intercept) and the extrapolated maximum yield loss, also varied according to the different growing conditions, including experimental treatments and other husbandry operations. These differences must be considered when assessing the economic potential of a control measure such as fungicidal seed treatment.
SUMMARY Five rat monoclonal antibodies (MAbs) specific for U.K. isolate B of barley yellow dwarf virus (BYDV) have been produced and tested. The reactions of the MAbs against a range of isolates of known vector specificity from the U.K., U.S.A. and Sweden were compared and a provisional serological correlation suggested. A survey of 90 U.K. field isolates showed that they were of the same serological groupings as the typed isolates, and that the panel of MAbs could be used to characterize field isolates of BYDV. Two of the MAbs were produced in large quantities in ascitic fluids; antibody partially purified from them and conjugated to alkaline phosphatase was used successfully in direct ELISA.
The ability of mepiquat chloride and chlormequat growth retardants to modify grain yield components and stem length in two contrasting spring barley cultivars was evaluated in 2 years of small scale field experiments in central southern England. Interactions with plant population density and sowing date were studied.
The mid-tall cv. Koru was more responsive than the shorter high tillering ‘erectoides’ cv. Goldmarker. Early treatments of mepiquat chloride (applied before the start of main shoot stem elongation) on Koru raised grain yield/plant in both years. Early treatments with chlormequat and later applications (during main shoot stem elongation) of either retardant were largely ineffective. Yield increases were achieved by raising the number of spikes/plant along with the number of grains/spike and the above-ground biomass in certain later-formed, lower ranking shoots.
A medium plant population density (250 plants/m ² ) allowed the best response to early treatment with mepiquat chloride, as did a normally-timed sowing in contrast to a late one. Retardant-induced improvements in yield components in Koru were positively correlated with plant height, the result of over-compensation in the length of upper internodes.
It appears that effective treatments reduced the dominance of the main shoot during tillering, allowing greater initiation and survival of florets (grain sites) in smaller shoots.
This study examined extent of hyphal growth of Gaeumannomyces graminis var. tritici (Ggt) in seminal roots of wheat seedlings grown from seed of varying weight (12-60 mg). Hyphal invasion, measured microscopically in the inner cortex, endodermis and stele of root sections and in the early formation of stelar lesions, was found to be influenced in a complex manner by weight of seed. As weight of seed was increased, invasion of the inner cortex decreased linearly while invasion of stelar tissue varied in a non linear manner. These findings show that weight of seed must be considered when comparing levels of infection in seedlings of different cultivars of wheat.
Methods are described, for use with the Technicon Auto Analyzer, that have been successfully used in the determination of nitrogen, phosphorus and potassium in plant materials. Nitrogen is determined as the indophenol-blue complex on an aliquot of solution after digestion by a micro-Kjeldahl technique. Alternative methods are suggested for the final determination of nitrogen dependent on the range of values expected. The “bias” method is extremely sensitive to small variations in nitrogen levels, and, because of this high sensitivity, the recorder signal-to-noise ratio must be high. Methods are suggested for obtaining a maximum signal-to-noise ratio. Phosphorus and potassium are analysed at the same time on the same sample of ash solution with a single manifold. Phosphorus is determined colorimetrically by the yellow phosphovanadate complex, and potassium by flame photometry by using an internal standard of lithium nitrate. Nitrogen determinations can be carried out at a rate of 40 samples per hour, and phosphorus and potassium together at a rate of 60 samples per hour. The accuracy of these determinations is better than those obtained by other recognised techniques.
Winter wheat cv. Avalon was sown in autumn 1981, 1982 and 1983 on a clay loam soil following two cereal crops. Multifactorial experiments tested the effects of combinations of the following eight factors, each at two levels: rotation, sowing date, timing of nitrogen, amount of nitrogen, growth regulator, pesticide, spring fungicide and summer fungicide.
The best 16-plot mean grain yields in 1982–4 were respectively 8·7, 10·2 and 11·1 t/ha. Rotation had the largest effect on grain yield. Wheat following barley was severely infected with take-all and yielded, on average over 3 years, 2·2 t/ha less than wheat following oats. Take-all was more severe on wheat sown in mid-September than in mid-October; its effects on yield were lessened by early timing of N in 1982. Take-all decreased growth and N uptake mainly after anthesis, and also number of ears and dry weight per grain. Sowing in mid-September compared with mid-October decreased yield of wheat after barley by an average of 0·8 t/ha because take-all was more severe. Early sowing had negligible effects on grain yield of wheat after oats, but increased straw dry weight by 1·1 t/ha.
Spring fungioide increased yield by an average of 0·3 t/ha. Effects were larger after barley than after oats, associated with a greater incidence of eyespot after barley. Summer fungioide increased yield by an average of 0·3 t/ha. Foliar diseases were slight in all 3 years. Fusarium ear blight and sharp eyespot were prevalent in 1982 and were not well controlled by the fungioide treatments. Fungicide temporarily decreased the incidence of some components of the mioroflora on the ears. Pesticide increased grain yield of wheat after oats only in 1984, when aphids on the ears were numerous. Aphids were present on early-sown plots in all three autumns but there was little barley yellow dwarf virus infection even without pesticide. Pesticide always decreased the number of nematodes after harvest to fewer than present before sowing. Populations never approached levels expected to affect yield.
Early N application (main application early March) resulted in a larger grain yield in 1982 than N applied a month later. In 1983 and 1984 grain yield and N uptake by the grain were greater with the late application, especially when wheat was sown early. The soil contained more mineral N in the autumn of 1982 and 1983 than in 1981. Straw weight was always greater with early than with late application. Increasing the amount of N applied from 163 to 223 kg/ha increased N uptake by 40 kg/ha and grain yield by 0·5 t/ha after oats and by 0·6 t/ha after barley. N uptake in grain plus straw by the best yielding crops ranged from 205 kg/ha in 1982 to 246 kg/ha in 1984.
Chlormequat applied at the start of stem extension shortened the stems at maturity by 2 cm each year. In 1984 it inoreased yield of early-sown wheat by 0·3 t/ha and also decreased lodging, which did not occur in the first 2 years.
Multifactorial experiments on winter barley cv. Igri grown after potatoes were made from 1981 to 1983 on silty clay loam soils at Rothamsted. All tested combinations of seven factors, each at two levels: with and without autumn pesticide (aldicarb), two sowing dates (September or October), with and without a fungicidal seed treatment (‘Baytan’), with and without spring and summer fungicides, two amounts of nitrogen, two times of applying nitrogen and with and without a growth regulator (‘Terpal’). Growth, development, yield, nitrogen uptake, pests and diseases were monitored. Sowing in September, fungicide sprays in spring and summer, and the growth regulator had the largest mean benefits on grain yield (+0·80, +0·56 and +0·34 t/ha respectively). Some factors interacted with sowing date; thus aldicarb, the fungicide sprays in spring and summer and the later timing of N all increased yield more on the September-than on the October-sown barley. The larger yields on the September-sown plots were associated with more ears/m2 (978 v. 744) and, in spite of fewer grains per ear (17·8 v. 20·1), more grains per m2 (17·6 v. 14·7 × 103), but lighter grains (39·2 v. 42·3 mg). The largest yields each year (ca. 8.0–8.5 t/ha) were obtained from September-sown barley fully protected from pests and from pathogens in spring and summer and given N in April rather than in March.The aphid vectors of barley yellow dwarf virus were sufficiently common and infective in two of the three autumns to infect the September-sown barley sufficiently that their control by aldicar b enhanced yield. Nematodes, slugs and dipterous stem borers were not numerous enough to be damaging in any year. Mildew in autumn was controlled by the seed treatment, but effects on yield were inconsistent. Mildew in spring and summer was more abundant on the October-than on the September-sown barley; it was controlled by fungicide sprays, which increased yield significantly each year. Leaf blotch was more abundant on the September-sown barley.
Field experiments made in 1984 and 1985 compared the effects of ammonium chloride with those of other nitrogen fertilizers applied to winter wheat in spring. The dressing was divided, 40 kg N/ha in March and 160 kg N/ha in April. In both years take-all in July was at levels which usually decrease yield, and take-all ratings were greatest in plots treated with ‘Nitro-Chalk’ (calcium ammonium nitrate) and least in plots treated with ammonium sulphate, but the differences were not statistically significant. Ammonium chloride and the other treatments, urea and ‘Nitro-Chalk’ with potassium chloride, had intermediate effects and the ranking of treatments according to disease was consistent in both years. In 1984 the mean yield was 8·27 t/ha, range 7·92 t/ha (with ammonium chloride) to 859 t/ha (with ‘Nitro-Chalk’) and in 1985, 821 t/ha, range 7·;42 t/ha (with ‘Nitro-Chalk’) to 8·55 t/ha (with ammonium sulphate). In both years treatments had no significant effects on yields and the relationship between yield and disease was obscured in 1985 because of highly correlated disease and block effects.
Whereas applying spring nitrogen all in the ammonium form seemed to decrease take-all slightly, the effects on yields of winter wheat were inconsistent. There is no evidence of extra benefit to be gained from applying the ammonium as ammonium chloride to crops at risk from take-all in this country, but there may be some benefit in applying KCl with ‘Nitro-Chalk’ top-dressings in the spring.
Two experiments compared yields of spring barley following barley, oats, beans (Vicia faba), red clover (cut) and (one experiment only) oil-seed rape, and tested effects of trefoil (Medicago lupulina) undersown in the preliminary crops of barley and oats. N fertilizer was applied at two rates to preliminary crops, and four rates to the final crop in each experiment. Barley following barley suffered severely from take-all disease (Gaeumannomyces graminis var. tritici); barley after other crops was little affected. Other recognized soil-borne diseases were unimportant. Barley yielded less after barley than after other crops except where excessive N fertilizer caused lodging. Clover and beans left N residues equivalent to about 88 and 44 kg fertilizer N/ha respectively; undersown trefoil left inconsistent N residues. Couchgrass (Agropyron repens) was more prevalent after barley than after other crops.(Received February 23 1978)
Experiments in 1985 and 1986, at Woburn Experimental Farm in Bedfordshire, tested the effects of fungicides, applied in autumn, and a growth regulator, applied at GS3O–31 or GS32–33 in spring, on winter barley grown on two contrasting soil types in each year. Leaf diseases did not become severe in any of the experiments but take-all ( Gaeumannomyces graminis var. tritici ) was prevalent in 1985. Triadimenol (‘Baytan’) was more effective than flutriafol (‘Ferrax’) in decreasing the severity of takeall and its activity against the disease was related to earliness of sowing.
Mean responses in grain yield to the fungicide treatments were mostly small and not significant but did not conflict with the hypothesis that crops on lighter soils benefit more from autumn fungicides than those on heavier soils. Mean effects of the growth regulator sprays were also small but they interacted with both soil type and season. Over the 2 years the later spray applied to crops on the heavier soil gave the largest mean response. Sprays applied to crops on lighter soils were often detrimental to yield, especially in 1985.
Winter wheat growing on a silty clay loam soil was protected from rainfall by a mobile shelter for 100 days from tillering to maturity. During this time the crop was either irrigated according to demand or grew on stored soil water. The effects of this high and low water supply, in combination with a high and low N supply, on root and shoot growth and water uptake were studied.
The crop given both N and water yielded 9.7 t/ha of grain (85 % DM), drought reduced this to 7.9 t/ha, low N to 4.3 t/ha and drought and low N to 3.8 t/ha. Yield reductions were mainly due to fewer grains being produced.
Little root growth occurred in the topsoil during the drought but there was compensatory growth in the subsoil provided that N fertilizer was given. The droughted crops rooted to 160 cm, about 20 cm deeper than the irrigated crops, but the amount of root in the deep subsoil was very small, less than 0.1 cm/cm3 ai 140–160 cm, compared with 5–9 cm/cm3 in the topsoil.
The crop demand for water at any given time was partitioned throughout the root system but atmospheric demand was only met whilst the topsoil was wet. The fertilized, droughted crop extracted all of the potentially available water to a depth of 80 cm and a mean rooting density of 1 cm/cm3 was necessary to achieve this. Uptake from below this depth was limited by root growth.
The limiting value of the potential soil water deficit was 170 mm, and weather records showed that this would be exceeded one year in ten, on average. The likelihood of yield reduction due to drought could be reduced on this soil by improving root growth below 80 cm depth, although the chances of achieving this are low as root growth was probably limited by poor soil structure.
Suction traps operating at low level (1 5 m) were used to catch live alate Rhopalosiphum padi, Macrosiphum (Sitobion) avenae and Metopolophium dirhodum which were tested for transmission of barley yellow dwarf virus (BYDV). The first species caught and infective was R. padi, followed by M. (S.) avenae infective some 2–3 wk later and M. dirhodum 3–4 wk later still. Never more than 11-5% of the annual catch of any species transmitted BYDV and the proportion fluctuated from week to week and between seasons in different years.
The relative abundance of infective vectors of ths three species varied; annual numbers of infective M. (S.) avenae and M. dirhodum varied inversely with infective R. padi, the latter also usually transmitted severer virus. The results of the infectivity tests have been compared with the catches of these aphids by the Rothamsted Insect Survey and show that numbers of alate aphids do not necessarily indicate the likely incidence of BYDV.
A method is presented in which inorganic nitrite and nitrate are determined automatically in blood. The dialysis unit in the automated system separates nitrite and nitrate from blood protein and thus eliminates any preliminary manual de-proteinisation procedure. The diazotisation and coupling reactions involving sulphanilic acid and N-(1-naphthyl)ethylenediamine form the basis of the method. Nitrate is reduced to nitrite by a zinc column incorporated into the system, and this feature enables a rapid change from nitrite to nitrate analysis and vice versa. The method is especially suitable for the analysis of a large number of samples. Recovery from blood is reproducible and almost 100 per cent. The limit of detection is 0·1 µg per ml for nitrite, and 0·2 µg per ml for nitrate, and less than 1·0 ml of blood is needed for complete analysis. Range expansion can substantially increase the sensitivity if needed.
The rapid determination of nitrate in crops, soils, drainage and rainwater by a simple field method using diphenylamine or diphenylbenzidine with glass fibre paper
- R J B Williams
The infectivity index and barley yellow dwarf virus
- Plumb
Effect of triadimenol seed dressing on vegetative growth in winter wheat
- Anderson
Manual of Plant Growth Stage and Disease Assessment Keys. Ministry of Agriculture, Fisheries and Food
- Anon
The epidemiology and prospects for control of barley yellow dwarf virus in autumn- and spring-sown crops
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A spraying machine for small plot experiments
- Wilson
The prediction of nitrogen fertiliser rates from mineral N in the soil in spring
- F V Widdowson
Effects of fungicides and their timing on plant biomass, disease and yield of winter barley
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Research and Development Reports
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Effects of triadimenol-containing seed treatment on winter wheat infected with take-all
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Opportunities for the integrated control of barley yellow dwarf viruses in Uk
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The influence of rate and timing of autumn applied pyrethroid and carbamate insecticide sprays on the control of barley yellow dwarf virus in English and French winter cereals
- Barrett
Take-all disease in wheat (Triticum aestivum L.): phenotypic changes due to seed size and inoculum concentration
- Riveros