Effects of eyespot on the yield of winter wheat

In two experiments, on Julia and Zephyr spring barley, evidence was obtained that the development of powdery mildew in sprayed plots depended very much on their proximity to unsprayed crop. The effective period of control achieved with one spray was greater where plots were well separated from unsprayed crop than where they were surrounded by or very close to unsprayed crop. There is probably a risk that small plot experiments may not only underestimate the potential effectiveness of fungicides in agricultural practice, but also give misleading information on optimal spray timing.     

Effects of crop debris and cultivations on the development of eyespot of wheat caused by Oculimacula spp.

Results from a series of crop sequence and single-year experiments that tested different straw and cultivation treatments in a total of 11 site–season combinations confirmed previous evidence that the development of eyespot disease in cereals can be decreased by debris in the seed bed even if that debris includes eyespot-infected stem bases, which are the principal sources of primary inoculum. Two of the experiments, which followed non-cereal break crops and tested the effects of crop debris applied after ploughing or tining on eyespot in winter wheat that was artificially inoculated with Oculimacula spp., provided convincing evidence that the effects can be attributed to the debris per se, and not to any associated husbandry practices. There were often larger effects on disease in summer than in spring or on severity than on incidence suggesting that the effects of debris cannot be explained solely by effects on inoculum or initial infection, and that debris has a disease-suppressive effect.     

The effect of temperature on eyespot (Cercosporella herpotrichoides) in wheat seedlings

When seedlings of the winter wheat cultivars Cappelle-Desprez, Champlein and Hybrid 46 were artificially infected with mycelial inoculum of Cercosporella herpotrichoides Fron, the number of leaf sheaths penetrated by the pathogen increased with temperature over the range 6-18^oC. Rate of growth of the pathogen on agar also increased with temperature over this range. Temperature had little effect on differences between cultivars in number of leaf sheaths penetrated.     

Effects of temperature on the development and growth of winter wheat roots

Winter wheat was sown on 2 dates with 3 levels of nitrogen fiertiliser (0, 50 and 200 kg N ha⁻¹) in one year and on 2 sites in a followign season. Shoot and root development and growth were measured between emergence and anthesis in the first season and emergence and 7 mainstem leaves in the second. Differences in temperature and light regime led to significant differences in shoot and root development and growth between sowing dates. A thermal time-scale, based on soil surface or air temperatures, with a base of 0°C, adequately described the production of mainstem leaves and nodal root axes over all treatments. Autumn applied nitrogen had little effect on development. Shoot growth and green area index increased exponentially with thermal time prior to spring nitrogen application and the completion of canopy development. Early-sown crops had larger root systems than late-sown crops prior to winter and this divergence was retained until anthesis. The relationship between root growth and thermal time was little better than with days after sowing and was not improved by either varying the site of temperature measurement or the base temperature used for calculation. Differences in soil texture and drainage, between sites, led to significant changes in root length distribution. Although spring applied nitrogen generally increased root length, its effects were inconsistent. There was a curvilinear relation between root length and the amount of photosynthetically active radiation (PAR) intercepted; this relation was unaffected by sowing date or nitrogen treatment. The amount of root produced per unit PAR decreased as the season progressed, reflecting the decrease in the proportion of total dry matter partitioned to the root system.     

Effects of temperature on the development and growth of winter wheat roots

Wheat plants were grown in columns of soil until early stem elongation at a wide range of constant root temperatures. Two light environments were imposed and three levels of nitrogen fertilizer added at sowing. Shoot and root development and growth were measured by destructive sampling to investigate the combined effects of temperature and changing nutrient and assimilate supply. Both mainstem leaf and root axis production were linearly related to thermal time above a base temperature of 0°C. Low irradiance affected the appearance of mainstem tillers and associated nodal root axes. Nitrogen had little effect on shoot or root development but increased shoot area between 6 and 8 mainstem leaves. Higher temperatures and supplementary light resulted in larger root systems when compared at equivalent times after sowing. Total root length and root dry weight increased exponentially with thermal time, based on the mean of 4 cm soil and 2 cm air temperatures, but no single relation existed for all temperature and light treatments. Total plant dry matter, root length and root dry weight increased linearly with accumulated, intercepted, photosynthetically active radiation. Root growth responded less than the shoot to supplementary light. Increasing temperature reduced the proportion of root weight to total plant weight.     

Effects of irradiance and water supply on grain development in wheat

The effects of two levels of irradiance and of water supply on grain development in two cultivars of winter wheat were studied by imposing treatments during the phases of cell production and cell expansion in the endosperm. The storage capacity of the grain was determined by cell number in the endosperm, which was reduced by both treatments during the cell production phase. Changes in cell number caused by the treatments were due to changes in the rate of production of cells; the duration of the cell production phase was constant. Weight per grain at maturity was proportional, both within and between cultivars, to the number of endosperm cells, except when treatments altered the supply of assimilate to the grain during the cell expansion phase. Reducing irradiance and water during the cell expansion phase decreased the rate of accumulation of dry matter in the grain and reduced weight per grain at maturity, with no effect on the duration of grain filling. Shrivelled grain resulted from a failure of the endosperm cells to fill completely, and was characterised by a reduction in the number of ‘B’-type starch granules.     

Effects of temperature and water potential on the germination of muskmelon cultivars

The rate and final germination of four muskmelon cultivars (Cucumis melo) were examined in response to incubation temperatures of 20, 26 and 32°C. Germination was also characterised at 26°C pr 32°C over a range of water potentials from 0 to - 1000 kPa achieved with solutions of polyethylene glycol. The germination of one cultivar, TAM-Uvalde, was consistently slower at 20°C than at 26°C or 32°C. The other three cultivars, Perlita, TAM-Dew and Greenflesh, were inhibited by incubation at 32°C. However, the germination responses of cvs Perlita, TAM-Dew and Greenflesh at 26°C or 32°C improved as water potentials were reduced from 0 to – 200 or – 400 kPa. Cv. TAM-Uvalde was extremely sensitive to water stress and failed to germinate at water potentials below – 600 kPa when incubated at 26°C. The inhibition of germination at low water potentials was partially reversed in all cultivars by increasing the incubation temperature from 26°C to 32°C. It is suggested that the inhibition of germination at 0 kPa (distilled water) was due to a seed coat-mediated barrier to oxygen that could be reversed by removal of the seed coat or exposure to an oxygen-enriched atmosphere.     

Observations on take-all and eyespot diseases of wheat in Yorkshire

Wheat crops were surveyed in Yorkshire from 1944 to 1946 on farms where crops were reported to be unsatisfactory. Take-all ( Ophiobolus graminis (Sacc.) Sacc.) and eyespot ( Cercosporella herpotrichoides Fron.) were both found to be present; the latter is the most serious trouble on the better wheat lands.
The variation in the incidence of these diseases on selected farms during the three seasons has been compared.
The effect of rotation has been examined; both diseases were found to be encouraged by too frequent cropping with wheat or barley. The incidence of disease in wheat crops following a 1-year seeds ley was found to be influenced by the nurse crop used to undersow the seeds, and also by the time at which the ley was ploughed up. Oats were found to be preferable to either wheat or barley as a nurse crop, and in 1946 late ploughing considerably reduced the amount of eyespot disease present in the following wheat crop.
A 1-year ley is considered to be of too short a duration to ensure the disappearance from the soil of Ophiobolus graminis and Cercosporella herpotrichoides surviving from the previous crop, and a period of 2–3 years is suggested as being desirable.     

Effect of previous crops on the incidence of eyespot on winter wheat

Surveys of winter wheat from 1939 to 1946 show that eyespot (Cercosporella herpotrichoides Fron.) occurs throughout Britain and that its incidence depends largely on previous cropping and on weather. Examination of 551 crops on land whose cropping for the previous 4 years was known showed that the incidence rose steadily with increasing numbers of preceding wheat and barley crops: where neither crop had been taken for 4 years the proportion of crops with more than 70% infected straws was 2%, rising to 45% where three or four such crops had been taken and the average straws infected rose from 6 to 55%.
The percentage infection to be expected in various groups of crops was calculated from previous cropping; it was compared with the actual infection and so used to assess the importance of other factors in determining the incidence of eyespot. High spring rainfall, early sowing and a dense plant increased incidence and low spring rainfall, late sowing and a thin plant reduced it.
Eyespot was not usually severe on newly ploughed grassland until the third or fourth crop of wheat, but under very wet conditions it was sometimes severe in the second crop.
Oats is much less susceptible than wheat or barley, but some crops were found with a third of their straws infected.
A brief survey of winter wheat in Holland suggested possible causes for the rise and fall of eyespot in recent years and for its present lower incidence there as compared with East Anglia.     

Effects of combined water potential and temperature stresses on Cryptosporidium parvum oocysts.

Hosts infected with the parasite Cryptosporidium parvum may excrete oocysts on soils in watersheds that supply public drinking water. Environmental stresses decrease the numbers of oocysts after deposition on soils. However, the rates and effects of combined stresses have not been well characterized, especially for the purposes of estimating decrease in numbers. We subjected oocysts to combined stresses of water potential (-4, -12, and -33 bars), above-freezing temperatures (4 and 30 degrees C), and a subfreezing temperature (-14 degrees C) for 1, 14, and 29 days and one to six freeze-thaw cycles (-14 to 10 degrees C) to estimate coefficients to characterize population degradation using multiplicative error and exponential decay models. The experiments were carried out in NaCl solutions with water potentials of -4, -12, and -33 bars, in combination with temperature stresses at levels that could be expected in natural soils. Increased water potential increased the rate of population degradation for all temperature conditions investigated. Enhanced degradation leads to estimated rates of population degradation that are greater than those that have been reported and used in previous studies conducted to assess risk of water supply contamination from sources of C. parvum.     

Effects of temperature and water content on the secondary structure of wheat gluten studied by FTIR spectroscopy

The effect of temperature on gluten conditioned at the following water contents, 0%, 13%, and 47% (wet weight basis), was studied by FTIR spectroscopy over the temperature range of 25-85 degrees C. A detailed discussion of the assignment of the amide I band is given. At 0% hydration no changes in the secondary structure with temperature could be detected; spectra were consistent with a tight disordered structure with many protein-protein interactions. At 13% hydration, distinctive changes occurred in the low-frequency region of the amide I band (1,630-1,613 cm(-1)). This was attributed to changes in the beta-sheet structure. On cooling to 25 degrees C, these changes were mainly reversed. It was noted that most of the changes observed occurred above the glass transition temperature. At 47% hydration, more complex changes took place: as the temperature was raised distinct bands at 1,630 and 1,613 cm(-1) merged. However, this process was partially reversed, with recovery of both bands, on cooling. The significance of these results in relation to other changes in gluten proteins in flour and dough with temperature and water content is discussed.     

Effects of temperature,pH and water potential on growth of four fungi with disease biocontrol potential

Effects of temperature, pH and water potential on blomass production or hyphal extension of Gliocladium virens (G20) and three Trichoderma isolates were determined in vitro. Optimum blomass production occurred between 20 and 30°C and at pH ranges between 4.6 and 6.8. Two isolates of T. viride grew at 5°C and G. virens grew at 35°C but no isolates grew at 40°C. Hyphal extension rates and conidial germination of all fungi declined with decreasing water potential over the range -0.7 to -14.0 MPa. In general, growth rates for each isolate were lower on potato/dextrose agar with water potential adjusted with polyethylene glycol than when adjusted with NaCl or glycerol. No mycelial growth or spore germination occurred on agar at-14.0 MPa.The authors are with the Microbiology and Crop Protection Department, Horticulture Research International, Littlehampton, West Sussex BN17 6LP, UK. J.M. Whipps is the corresponding author     

Effects of temperature on hatching and development of Nematospiroides dubius in aerated water.

Fresh eggs obtained from female Nematospiroides dubius were cultured at temperatures ranging from 5 degrees C to 33 degrees C. Hatching occurred between 5 degrees C and 30 degrees C; third stage larvae were obtained between five degrees C and 25 degrees C. The minimum time required from hatching to development to the third stage was 3-6 days (at 20 degrees C) and the maximum was seven days (at 5 degrees C). Larvae cultured at higher temperatures were smaller than those cultured at lower ones.     

Influence of direct-drilling of winter wheat on incidence of take-all and eyespot

Winter wheat drilled directly into stubble or pasture treated with paraquat to kill the vegetation has been found to be less severely attacked by take-all (Ophiobolus graminis (Sacc.) Sacc.) and eyespot (Cercosporella herpotrichoides Fron) than wheat drilled after cultivation. The reduction of take-all is associated, not with a direct effect of the chemical, but with factors, resulting from the technique, which limit the rate of spread of the fungus in the undisturbed soil.     

玉米秸秆还田配施生防放线菌S024对麦田土壤微生物及小麦纹枯病的影响

采用大田人工接种的方法,研究了玉米秸秆不同还田量以及玉米秸秆还田与生防放线菌S024同时施用对麦田土壤微生物、小麦纹枯病和小麦产量的影响。结果表明:玉米秸秆还田能够显著增加土壤细菌和放线菌数量;秸秆还田同时施用生防菌,拔节期土壤放线菌数量与不还田(对照)相比,平均增加50%,土壤中小麦纹枯病菌的数量与对照相比减少了20%。秸秆还田处理在拔节期对小麦纹枯病有较好的防病效果,其中生防菌+秸秆加倍还田(9000kg.hm-2)处理的防病效果最好,病情指数减退率达57.4%。玉米秸秆还田对小麦有一定增产作用,其中生防菌+秸秆加倍还田处理增产幅度最大,增产23.1%。     

Studies on sharp eyespot disease of cereals: Effects of the disease on the wheat host and the incidence of disease in the field

Greenhouse and field experiments showed that sharp eyespot disease can reduce establishment in wheat seedlings. Increasing disease severity caused a decrease in height and dry weight of surviving seedlings. Infection by the pathogen caused a reduction in tillering. Experiments also showed that a high incidence of disease can cause a reduction in the yield of grain of mature plants, but the disease level necessary for such effects is far higher than that usually encountered in the field. Survey work in the East of Scotland in 1963-65 showed a high percentage of crops infected with the disease. But even in 1964, a year of comparatively high disease incidence, there were few crops with a level of infection as high as that shown to affect yield.     

Influence of temperature gradients on leaf water potential

Water potential was monitored at nine locations along single maize (Zea mays L.) leaf blades with aluminum block in situ thermocouple hygrometers. Water potential showed a continuous decrease toward the tip, with a 2- to 4-bar difference between leaf base and tip under both moist and dry soil conditions. The water potential difference between the soil and the leaf base was about 4 bars. Water potentials decreased during the day and during a drying cycle, and increased at night and after irrigation. Heating a band of a leaf to 40 C or cooling it to 7 C had no influence on the water potential of the affected portion when this was corrected for hygrometer output over standard calibrating solutions at the respective temperatures. Heating or cooling a portion of a leaf had neither short nor long term effects on water potential of more distal leaf portions continuously monitored by hygrometers in dew point readout. Water potential fluctuated with an amplitude of about 1.5 bars and an irregular period of 10 to 30 minutes. Measurements with silver foil in situ psychrometers gave similar results.     

Effects of water stress on development, operation and gene expression of cyanide-resistant respiratory pathway in wheat

Osmotic dehydration of wheat seedlings in-0.5 MPa polyethylene glycol (PEG) solutions for 24, 48 and 72 h resulted in mild, moderate and severe water stress respectively in leaves, but only caused mild water stress in roots as reflected by the changes in relative water content (RWC). In response to the above water stress conditions, leaf total respiratory rate (V_t) decreased progressively, and the alternative pathway (AP) capacity (V_(alt)) and its actual operation activity (ρV_(alt)) decreased more severely. Water stress also led to continuous reduction in cytochrome pathway (CP) activity ((ρ' V_(cyt)) and different changes in the contribution of ρV_(alt) and ρ' V_(cyt) to V_t in leaves, with ρV_(alt)/V_t decreasing and ρ' V_(cyt)/V_t increasing. The change pattern of root V_t was similar to that of its RWC, while root V_(alt) and ρV_(alt) were found to decrease during the first 24 h of stress and thereafter recover to a level close to that of the control (O h). These data indicate that the alt     

冬小麦品种DS1号生育进程的温光效应

DS1号是适于 2 2 .5 kg/hm2 播种量的秋播冬小麦品种。为了掌握其温光反应特性 ,为确定它的适宜种植范围提供试验依据 ,2 0 0 1年和 2 0 0 2年 ,用这个小麦品种在人工气候箱内进行了 8种不同温光组合的生态模拟试验。参试品种是 DS1号。每台气候箱的体积为 5 0× 5 0× 1 0 0 cm3。试验过程中 ,箱内相对湿度是70 %～ 78%。光照强度为 90 0 0 lx。试验结果显示 ,在不同处理中 ,出苗至抽穗过程中 ,≥ 5℃积温和天数差异极大。结果表明 ,低温不是唯一的春化条件。在 8种不同的处理中 ,植株抽穗前 ,表现了不同的温光效应。在生育前期 5℃的处理中 ,可以完成春化 ,与之配合的 1 6h光照的长日条件或 8h光照的短日条件均可。在2 0℃和 8h光照的处理中 ,未表现出短日春化效应 ,或抽穗期显著拖长。短日春化可能要有一定的光照强度相配合。生育前期或直至抽穗前 ,在 2 0℃和 1 6h长日条件下 ,可以通过“非春化途径”完成抽穗前的生育进程 ,出苗～生理拔节和出苗～抽穗阶段并不拖长或略长     

Effects of low temperature on wheat leaf proteins

Finnish wheat cultivars, winter wheat ‘Vakka’ and spring wheat ‘Apu’, grown for 9 days at 25° and then for 52 days at 2–4°, were called ‘hardened’. Proteins and esterases of young leaves were resolved by polyacrylamide gel electrophoresis (PAGE), porosity gradient PAGE (poroPAGE), isoelectric focusing (PAGIF) between pH 3 and 9, and by Na-dodecylsulfate (SDS)-PAGE. Hardened and unhardened leaves have different protein patterns after PAGE, PAGIF, poroPAGE and SDS-PAGE, respectively, as well as for esterases after PAGE and PAGIF. The PAGIF patterns of esterases show distinct changes of two bands especially for hardened leaves of winter wheat, one appearing, the other one disappearing.