The economics of reduced-rate insecticide applications to control aphids in winter wheat

Applications of pirimicarb and fenvalerate at full-rate and at a range of reduced dosages were applied on fields of winter wheat between 1983 and 1988 in West Germany. The relative effects of these treatments on the control of cereal aphids varied according to the growth stage at which spraying took place and the size of the aphid populations. The economic profitability of these treatments depended on the extent of post-treatment recovery of the aphid populations, the cost of control and the crop value. Under certain circumstances the high efficiencies of commonly-used insecticides at full dose-rate are not necessary to gain effective aphid control economically; a better return can be made by reducing the quantity of active ingredient per hectare.     

小麦种质抗倒性的评价和抗倒性状的相关与通径分析

对９６份小麦种质资源的抗倒性进行了鉴定评价,筛选出高抗型材料９份,其中４份是丰源,表明抗倒性能够与丰产性状很好地协调结合。对抗倒性状的相关分析表明,在株高相差较大的情况下,株高和重心高度对抗倒性十分重要。但在对株高相差不大的情况下,茎秆的机械强度是主要决定因素,对于株高较高的材料,重心高度对抗倒性有较大影响;对于较矮的材料,基部第一节间长度则较为重要。通径分析结果进一步表明,茎秆机械强度对抗倒性的     

Climatic impacts on winter wheat in Oklahoma and potential applications to climatic and crop yield prediction

Climatic anomalies can pose severe challenges for farmers and resource managers. This is particularly significant with respect to gradually developing anomalies such as droughts. The impact of the 1995-1996 drought on the Oklahoma wheat crop, and the possibility that predictive information might have reduced some of the losses, is examined through a combined modeling approach using climatological data and a crop growth model that takes into account an extensive range of soil, climatic, and plant variables. The results show potential outcomes and also illustrate the point at which all possible climatic outcomes were predicting a significantly low wheat yield. Based on anecdotal evidence of the 1995-1996 drought, which suggested that farmers who planted at different times experienced different yields, the model was run assuming a variety of different planting dates. Results indicate that there is indeed a noticeable difference in the modeled wheat yields given different planting dates. The information regarding effectiveness of planting date can be used in conjunction with current long-range forecasts to develop improved predictions for the current growing season. This approach produces information regarding the likelihood of extreme precipitation events and the impact on crop yield, which can provide a powerful tool to farmers and others during periods of drought or other climatic extremes.     

The effect of nitrogen and growth regulators on stem and root characteristics associated with lodging in two cultivars of winter wheat

The effects of nitrogen and plant growth regulators (stem shorteners)on root and shoot characteristics associated with lodging resistancewere investigated in two winter wheat (Triticum aestivum L.)cultivars of contrasting lodging resistance: the susceptibleGalahad and the resistant Hereward. The morphology and mechanicalstrength of the stems and anchorage systems grown at two levelsof nitrogen and with or without growth regulators were measuredand related to the incidence of lodging recorded in a fieldtrial. In both cultivars high levels of nitrogen increased theheight of the stem, thereby increasing the ‘self-weight’moment transmitted into the ground and weakened both the stemsand the anchorage coronal roots. As a result, the anchoragestrength was also reduced, plants failing in the root systemin simulated lodging tests. Growth regulators, in contrast,had little effect on the bending strength of the shoots androot systems, but reduced plant height so that the over turningmoments generated by the weight of the shoot were less. Therewere also differences between cultivars: Galahad plants hadweaker anchorage due to the smaller number and lower strengthof the coronal roots. The morphological and mechanical measureswere used to calculate a safety factor against both stem androot lodging. Five factors were found to influence the safetyfactors, these were: cultivar type, the type of lodging, therate of nitrogen and growth regulator application, and time,being lowest in Galahad plants at high levels of nitrogen andwithout growth regulators and at grain filling when the earswere heaviest. This was consistent with the observed patternof lodging: root lodging occurred at grain filling and onlyin Galahad which had been treated with high nitrogen rates,most strongly in plants without growth regulators. Key words: Lodging, safety factors, anchorage, ‘self-weight’ moment     

Effects of phosphorus nutrition on tiller emergence in wheat

Phosphorus (P) deficiency limits the yield of wheat, particularly by reducing the number of ears per unit of area because of a poor tiller emergence. The objectives of this work were to (i) determine whether tiller emergence under low phosphorus availability is a function of the availability of assimilates for growth or a direct result of low P availability, (ii) attempt to establish a quantitative relation between an index of the availability of P in the plant and the effects of P deficiency on tiller emergence, and (iii) to provide a better understanding of the mechanisms involved in tiller emergence in field-grown wheat. Wheat (Triticum aestivum L., cv. INTA Oasis), was grown in the field under drip irrigation on a typic Argiudol, low in P (5.5 μg P g^-1 soil Bray & Kurtz I) in Balcarce, Argentina. Treatments consisted of the combination of three levels of P fertilization 0, 60 and 200 kg P₂O₅ ha^-1, and two levels of assimilate availability, a control (non-shaded) and 65% of reduction in incident irradiance from seedling emergence until the end of tillering (shaded). Phosphorus treatments significantly modified the pattern of growth and development of the plants. Shading reduced the growth and concentration of water-soluble carbohydrates in leaves and stems. Leaf photosynthetic rate at saturating irradiance was reduced by P deficiency, but was not affected by shading. At shoot P concentrations less than 4.2 g P kg^-1 the heterogeneity in the plant population increased with respect to the number of plants bearing a certain tiller. At a shoot P concentration of 1.7 g P kg^-1 tillering ceased completely. Phosphorus deficiency directly altered the normal pattern of tiller emergence by slowing the emergence of leaves on the main stem (i.e. increasing the phyllochron), and by reducing the maximum rate of tiller emergence for each tiller. This revised version was published online in June 2006 with corrections to the Cover Date.     

甘肃省冬小麦生长发育对暖冬现象的响应

运用甘肃省天水、西峰两地1951-2005年的气温资料及天水、西峰农业气象试验站1981-2003年冬小麦物候观测资料,分析探讨了甘肃冬小麦种植区50多年的冬季气温变暖趋势及冬小麦生长发育过程对气候变暖的响应．结果表明：冬季气温升高对冬小麦生长发育产生了较大影响．在最近20多年,冬小麦越冬死亡率下降到2％以下,越冬天数减少了7～8d,整个生育期缩短8～10d,返青一开花期天数延长7d,这有利于冬小麦生产及气候资源的利用-同时,冬季气温升高及降水减少也使冬小麦产量稳定性变差,麦田病、虫危害发生率增加,给冬小麦的安全生产增加了不确定因素．     

Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.     

Temporal and spatial changes in aphid and parasitoid populations following applications of deltamethrin in winter wheat

The spatial and temporal effects of the pyrethroid insecticide, deltamethrin, on populations of cereal aphids and their primary parasitoids and hyperparasitoids were investigated in a large scale field experiment in winter wheat. Four hectare plots were treated at the recommended field concentration or a reduced concentration representing one twentieth of field rate. A control plot was left unsprayed. Invertebrate populations were sampled at sites within a grid layout covering the whole plots, enabling the use of geostatistical analysis. Hymenopteran populations were monitored using transparent sticky traps and suction sampling. Aphid populations were recorded by visual counts. Monitoring continued for 36 days after treatment. The full rate deltamethrin treatment resulted in initial reductions of aphid populations by 78%. Primary parasitoid and hyperparasitoid populations were reduced in suction samples by 90% and 47% respectively, when corrected for control fluctuations. The reduced deltamethrin concentration caused reductions of aphid, primary parasitoid and hyperparasitoid populations of 40, 60 and 54% respectively. Aphid population recovery over the full rate plot occurred slowly and in a patchy manner following treatment. No significant reinvasion gradients were detected. Aphid population density recovered more rapidly in the reduced rate treatment; with initial evidence for increased densities at the plot centre. Significant patterns of reinvasion were initially detected for both groups of Hymenoptera in the full rate treatment, suggesting that reinvasion of the sprayed area was taking place from untreated surrounding reservoirs. It was concluded that experiments that examine pesticide impacts within small plots will lead to underestimates of effects on dispersive groups including parasitic Hymenoptera.     

Ways to reduce anti-nutritional substances in winter rye grain

The purpose of this research was to establish the nature and extent of the influence of microwaves and extrusion on the content of anti-nutritional substances of winter rye grain. There was performed two-factor laboratory experiment with the treatment of winter rye grain by electromagnetic waves of super-high frequency (microwave) on a LG MS-2042G installation and one-factor laboratory experiment with grain treatment using a MKP-30-500 extruder. Depending on the power and duration of the microwave treatment, the content of water-soluble pentosans decreased by 0.04–0.44% and the kinematic viscosity of the aqueous extract—by 2.4 times. As a result of extrusion processing, the content of water-soluble pentosans in the winter rye grain decreased by 1.34 times, the kinematic viscosity of the aqueous extract—by 2.42 times. For all the years of the research, extrusion has led to a certain decrease in starch in winter rye grain. During a 3-year period the original grain of winter rye contained on average 59.9% of starch. After extrusion, the value of this indicator decreased by 2.0% amounting to 57.9%. During the extrusion process, starch is partially hydrolyzed to form intermediate carbohydrates-dextrins and then glucose. Our research has shown an increase in the content of soluble carbohydrates in extruded rye grain. During a 3-year period, the content of soluble carbohydrates in grain increased on average from 31.45 to 51.36%, i.e. by 19.91%. Treatment by microwaves and extrusion are effective ways to reduce the anti-nutritional substances of winter rye grain and significantly increase the proportion of rye grain in the diet of farm animals.

     

Efficient strategies to assess yield stability in winter wheat

Key message

Selecting contrasting environments allows decreasing phenotyping intensity but still maintaining high accuracy to assess yield stability.

Abstract

Improving yield stability of wheat varieties is important to cope with enhanced abiotic stresses caused by climate change. The objective of our study was to (1) develop and implement an improved heritability estimate to examine the required scale of phenotyping for assessing yield stability in wheat, (2) compare yield performance and yield stability of wheat hybrids and inbred lines, (3) investigate the association of agronomic traits with yield stability, and (4) explore the possibility of selecting subsets of environments allowing to portray large proportion of the variation of yield stability. Our study is based on phenotypic data from five series of official winter wheat registration trials in Germany each including 119–132 genotypes evaluated in up to 50 environments. Our findings suggested that phenotyping in at least 40 environments is required to reliably estimate yield stability to guarantee heritability estimates above 0.7. Contrasting the yield stability of hybrids versus lines revealed no significant differences. Absence of stable associations between yield stability and further agronomic traits suggested low potential of indirect selection to improve yield stability. Selecting posteriori contrasting environments based on the genotype-by-environment interaction effects allowed decreasing phenotyping intensity, but still maintaining high accuracy to assess yield stability. The huge potential of the developed strategy to select contrasting and informative environments has to be validated as a next step in an a priori scenario based on genotype-by-location interaction effects.

     

Warmer springs disrupt the synchrony of oak and winter moth phenology

Spring temperatures have increased over the past 25 years, to which a wide variety of organisms have responded. The outstanding question is whether these responses match the temperature-induced shift of the selection pressures acting on these organisms. Organisms have evolved response mechanisms that are only adaptive given the existing relationship between the cues organisms use and the selection pressures acting on them. Global warming may disrupt ecosystem interactions because it alters these relationships and micro-evolution may be slow in tracking these changes. In particular, such shifts have serious consequences for ecosystem functioning for the tight multitrophic interactions involved in the timing of reproduction and growth. We determined the response of winter moth (Operophtera brumata) egg hatching and oak (Quercus robur) bud burst to temperature, a system with strong selection on synchronization. We show that there has been poor synchrony in recent warm springs, which is due to an increase in spring temperatures without a decrease in the incidence of freezing spells in winter. This is a clear warning that such changes in temperature patterns may affect ecosystem interactions more strongly than changes in mean temperature.     

Photosynthesis and yield responses of ozone-polluted winter wheat to drought

Winter wheat (Triticum aestivum L. cv. Jingdong 8) was exposed to short-term high ozone treatment after anthesis and then was either well irrigated with soil water content (SWC) of 80–85 % (O₃+W) or drought treated (SWC 35–40 %, O₃+D). Short-term ozone exposure significantly decreased irradiance-saturated net photosynthetic rate (P _N) of winter wheat. Under good SWC, P _N of the O₃-treated plant was similar to that of control on 2 d after O₃-exposure (6 DAA), but decreased significantly after 13 DAA, indicating that O₃ exposure accelerated leaf senescence. Meanwhile, green flag leaf area was reduced faster than that of control. As a result, grain yield of O₃+W was significantly decreased. P _N of O₃+D was further notably decreased and green flag leaf area was reduced more than that in O₃+W. Consequently, substantial yield loss of O₃+D was observed compared to that of O₃+W. Although P _N was significantly positively correlated with stomatal conductance, it also had notable positive correlation with the maximum photochemical efficiency in the dark adapted leaves (F_v/F_m), electron transport rate (ETR), photochemical quenching (q_P), as well as content of chlorophyll, suggesting that the depression of P _N was mainly caused by non-stomatal limitation. Hence optimal soil water condition should be considered in order to reduce the yield loss caused by O₃ pollution.     

Components of partial resistance to Septoria nodorum in winter wheat

Components of partial resistance to Septoria nodorum were investigated in 10 cultivars of winter wheat having similar field resistances. The components measured were infection frequency, latent period, size, shape and rate of growth of lesions, spore production and its rate of increase. Latent period was found to be lognormally distributed. Some of the components of resistance were found to be significantly different between cultivars. Cluster analysis also showed that cultivars could be distinguished on the basis of their components of resistance. Principal components analysis indicated that resistance could be broken down into four underlying factors, three of which could be readily interpreted. The measurements of the components of resistance were combined in a model, the r-index, based on Van der Plank's r. The amount of variation between cultivars cast some doubt on the predictive value of the index but all the cultivar values were well within the range bounded by two ‘synthetic’ cultivars made up of combinations of either the most resistant or the most susceptible components. It is considered that the r-index has potential in screening for field resistance. The possibility of incorporating the most resistant-type components into one cultivar is discussed. The use of cultivar mixtures containing cultivars having similar field resistances is also discussed in the light of the variability found in this study.     

冬小麦抗氧化酶对冬季节律性日变温和非节律性变温的响应

通过对冬季室内和室外分别生长30d的冬小麦在节律性和非节律性融冻变温过程中抗氧化酶活力和渗透调解物含量变化的分析,揭示其在冬小麦适应日融冻胁迫中的作用。结果表明:生育期不同的室内(均温11℃,拔节期)和室外(均温1℃,分蘖静滞期)冬小麦叶片抗氧化酶和脯氨酸对日光强和温度节律变化的响应趋势是一致的,即随日出而增高,中午气温较高时最高,日落而降低;在非节律性变温处理中,室外冬小麦抗氧化酶活力和脯氨酸含量随气温上升至18℃而增高,气温迅速下降到-2.5℃而降低,经历冻-融-冻胁迫冬小麦生长良好。室内冬小麦抗氧化酶活力随气温降低到-6℃,叶片结冻,迅速下降,气温升高到18℃而增加,经历融-冻-融胁迫后植株死亡;室外冬小麦光合速率(Pn)和比室内的低,而抗氧化酶活力高于室内;冬小麦快速提高抗氧化酶活力和脯氨酸含量,抑制氧自由基积累、维护细胞水分平衡,这在适应冬季节律性融冻胁迫中起重要作用;暖冬中冬小麦较高的Pn和较低的抗氧化酶活力可能是引起冬小麦在"倒春寒"中死亡的生理原因。     

Analysis of spatial and yearly variation in winter survival of winter wheat

 Four years of winter survival data for winter wheat (Triticum aestivum L.) were collected on a loam soil located on the Central Experimental Farm at Ottawa, Ontario (45° 23′N, 75° 43′W). The site was low-lying and subject to frequent winter flooding and ice sheet formation. It appeared level although there was microtopographic variation with a range in elevation of approximately 0.15 m. The objective of the study was to gain insight into factors which might affect winter survival. Two varieties, a soft white and a hard red winter wheat, were planted in September. Crop establishment was measured in late fall and the percentage survival was measured in April of the following year. We assumed the large spatial differences in survival were not totally random, but rather were affected by spatial variation in environmental factors such as snow and ice depth, soil moisture and temperature. Hourly measurements of soil temperature at a depth of 0.05 m were recorded throughout the fall, winter and spring. Fall and spring soil moisture at the same depth were measured on the plot, as well as snow and ice depth at selected times throughout the winter. Measurements were taken on a grid covering the plot to help explain spatial variation in survival. In addition, detailed measurements of elevation were taken on a grid. Meteorological data were available from the nearby weather site. While soil temperatures were never low enough to kill plants according to the CERES model, the spatial variation in winter survival was associated with differences in elevation and the resulting surface drainage patterns. Received: 23 March 1998/Accepted: 21 October 1998     

Antifungal compounds in winter wheat resistant and susceptible to Septoria nodorum

The content of benzoxazinone compounds in Septoria nodorum resistant and susceptible wheat cultivars fell with time, reaching an undetectable level 3–4 wk after germination. The compounds were absent from field-grown plants extracted at growth stages 2–3, 6–7, 10, 10.5 and 11. Additional antifungal compounds were detected in healthy and diseased field-grown plants of both cultivars at all growth stages, although qualitative and quantitative differences in inhibitory activity were small and their role in resistance remains open to discussion.     

Identification of quantitative trait loci for productive tiller number and its relationship to agronomic traits in spring wheat

Productive tiller number (PTN), defined as the number of tillers that produce spikes and seeds, is a key component of grain yield in wheat. Spring wheat cultivars in the northern Great Plains of North America differ in PTN. The objectives of this study were (1) to determine the relationship of PTN to agronomic traits using recombinant inbred line (RIL) populations derived from crosses Reeder/Conan, McNeal/Thatcher and Reeder/McNeal grown under a range of environments, and (2) to identify and validate quantitative trait loci (QTL) associated with high PTN. Correlation between PTN and plot weight ranged from r = 0.4–0.6 among the populations based on combined means over years, and was positive in every environment for all crosses (P < 0.05). A genetic map generated for the Reeder/Conan RIL allowed identification of a QTL for PTN consistent over environments, located on chromosome 6B. The QTL on chromosome 6B (QTn.mst-6B) explained 9–17% of the variation of PTN and co-segregated with a QTL for yield in the Reeder/Conan RIL. QTn.mst-6B was validated by single marker analysis in the McNeal/Thatcher RIL, McNeal/Reeder RIL, and a set of near isogenic line (NIL) developed for QTn.mst-6B. The allele for high PTN significantly increased PTN by 8.7, 4, and 13% in the McNeal/Reeder RIL, McNeal/Thatcher RIL and Choteau/Reeder NIL, respectively. The allele for high PTN also had a significant positive effect on plot weight in the McNeal/Reeder RIL. Our results suggest that high PTN, controlled to a significant extent by QTn.mst-6B, contributed to increased yield potential over a range of environmental conditions. QTn.mst-6B may be useful for improving spring wheat in the northern Great Plains of North America and similar environments.