Climate in relation to deterioration of stored grain

Summary A hypothesis elucidating the basic relationship between abiotic climatic variates and the deterioration of stored grain by biotic agents was developed for the 41 crop districts in the Prairie Provinces of Canada. Principal component (7 variates measured) and canonical correlation (6 variates measured) analyses were applied to data from each of the 3 crop years (1967–1969), for each of the 3 principal component analyses and for each of the 3 canonical correlation analyses. The data consisted of crop district means of infestation reports from 2522 managers of grain elevators and also of representative meteorological observations from each crop district. The major variates measured were the number of reports of: hot spots, infestations of a) fungus beetles and mites, and b) Cryptolestes ferrugineus (Stephens), and grain fumigants. The climatic variates consisted of mean temperature, precipitation, and number of days above 20° C (68° F) for July, August and September. Three major components, which together explained 64–80% of the variation, indicated broadly similar trends in all analyses. The first component indicated that lower mean temperatures and larger numbers of cool days increased the incidence of fungus-induced hot spots in wet harvested grain. The second component indicated the extent of arthropod infestations: warmer weather increased C. ferrugineus infestation, whereas cooler weather increased infestation by mites and secondary insect species. The third component was a measure of precipitation. Canonical correlation analyses based on 1967 and 1969 data yielded canonical roots that were statistically insignificant at the 1% level. Analyses of 3 external abiotic and 3 biotic response variates based on 1968 data showed that only the first pair of canonical variates was significant, the degree of predictability (R _c ² ) being 56% (P<0.01). The analyses revealed that lower temperatures, a greater number of cool days, and higher precipitation increased the number of hot spots in 1968 confirming the findings of the principal component analyses. The pattern of hot spot development in relation to climatic characteristics was similar in all crop districts for all years examined. There was a linear relationship between climatic and biotic variates for all these crop districts but the degree of relationship varied geographically. The first and second principal component values for each crop district were ranked and plotted on a climatic map of the Prairie Provinces. The ranking showed that the incidence of hot spots and arthropod infestations was highest in the Sub-boreal and Humid southeastern regions, whereas the incidence was lowest in the Dry Belt region. C. ferrugineus was most common in the Humid southeastern region.Contribution No. 522 from Canada Department of Agriculture, Research Station, Winnipeg, Manitoba, R3T 2M9, Canada.     

Analysis and simulation modelling of population dynamics and bioenergetics ofCryptolestes ferrugineus (Coleoptera: Cucujidae) in stored wheat

The consequences of infestation of stored wheat by the rusty grain beetle, Cryptolestes ferrugineus (Stephens) was determined for 222 d at 30°C in 70-1 drums containing wheat at 13.5% moisture content. Temperature, grain moisture, seed damage, germination and weight, dust weight, fat acidity values (FAV), published data on growth, reproduction, survival and cannibalism rates and energy budget were used to develop a computer simulation model to simulate the population dynamics of C. ferrugineus at 30°C. In the insect-free control system, the fungi, Alternaria alternata decreased, Aspergillus glaucus group and Penicillium spp. increased, probably causing a rise in FAV of the grain. In the insect-infested system, C. ferrugineus could only eat the wheat germ of kernels that had a broken bran layer; 35.7% of the wheat germ or 914.6 J per 100 kernels was consumed. Within two generations after initial introduction, C. ferrugineus reached a peak in numbers and biomass polluting the ecosystem with excreta and remains, and accelerating the deteriorative process observed in the insect-free control system by increasing respiration temperature, FAV and reducing grain germination. After 87 d, the insect population declined to low levels. The simulation model provided a close match between the observed and predicted numbers of insect life stages and bioenergetic variables during the insect population growth phase. Simulation trials suggested that cannibalism of larger compared with smaller immature stages would be more wasteful of developmental time and energy, reducing the number of individuals reaching reproductive age, and that density-dependent fecundity was probably not an important regulatory mechanism of C. ferrugineus population dynamics in this study.     

Formation of Fusarium metabolites in barley grain

Summary The influence of moisture content and temperature during storage of grain on the formation of Fusarium metabolites was studied. Naturally and artificially contaminated barley grain samples were stored at 15%, 25%, and 30% moisture contents, and at temperatures of + 5°C + 25°C, and + 30°C. Time of storage varied between one week and six months and the occurrence of Fusarium species and metabolites was analysed. The only Fusarium metabolite detected was zearalenone. The extent of Fusarium contamination decreased during storage whilst the concentration of zearalenone increased. To avoid the danger of mycotoxicoses, grains must be dryed immediately after harvest and then stored at a low temperature.     

Microflora of stored grain in international trade

Although the temperature of grain in the holds of ships arriving in Japan from Argentina, Australia, Canada, China and USA during 1966–67 varied with the grain, country of origin, and season, it was likely to be determined by the temperature of the grain when it was loaded into the ships. Dockage level varied among bulks of the same type of grain, but the mean dockage in any one crop was always larger when originating from the USA than from other countries. Generally the viability of the grain was good, but when it was reduced, interaction of variety and time seemed to be the principal cause. Field fungi — non-pathogenic Alternaria, and the pathogenic Helminthosporium and Fusarium species — tended to die out, during transport, thus reducing the hazards of new pathogenic strains being distributed across international boundaries. The non-pathogenic field fungi, Cladosporium and Phaeoramularia, were persistent. Although common in grain shipments from all countries, species of Aspergillus and Penicillium varied quantitatively with the different grains. In this respect, more Aspergillus spp. were found in grains originating in the USA and Australia than those originating in Canada. The primary contamination by storage fungi appeared to be at the source, at or after harvest and in storage prior to export.     

Influence of mulching on the pattern of growth and water use by spring wheat and moisture storage on a fine textured soil

Eight tonnes ha^–1 of stubble were used to mulch spring wheat (Triticum aestivum) on a fine textured soil with the aim of controlling both transpiration and soil evaporation during the wet pre-anthesis phase to increase moisture supply during grain filling in the eastern wheatbelt of Western Australia. Mulching reduced leaf area per plant by reducing the culm number; consequently the green area index was reduced. Reduced culm number was associated with low soil temperature which at 50 mm depth averaged 7°C lower under the mulched crop relative to the control crop in mid-season. The smaller canopies of the mulched crop used 15 mm less water than those of the control before anthesis; this difference in water-use was due equally to reduced transpiration and soil evaporation. However, the mulched crop was unable to increase ET during grain filling, a response associated with the persistence of low soil temperature for most of the growth period. Hence, total ET for the season was significantly lower (18 mm) under the mulched crop than the control crop. At harvest, mulching did not have significant effects on total above-ground dry matter and grain yields, but it increased water use efficiency for grain yield by 18%, grain weight by almost 17% and available moisture in both uncropped and cropped plots by an average of 43 mm.To determine whether there was any residual effects of soil treatment on moisture storage during the summer fallow period, soil moisture was monitored both in cropped plots and uncropped plots, that were either mulched or unmulched during the growing season, from harvest in October 1988 until next planting in June 1989. Available moisture at next planting was correlated with moisture storage at harvest despite the differences in run-off, soil evaporation and fallowing efficiency (increase in moisture storage as a percentage of rainfall) between treatments during fallowing. Therefore, the mulched treatments had more moisture available (30 mm), mostly as a result of less water use during cropping in the previous growing season, than the unmulched treatment.The study shows that mulching may be used to restrain both transpiration and soil evaporation early in the season to increase availability of soil moisture during grain filling. Secondly, mulching during the previous growing season had little effect on soil moisture during the summer fallow period, however, the moisture saved by mulching during cropping was conserved for the following season. These results indicate the importance of evaluating mulching of winter crops in terms of crop yield in the subsequent growing season as well as in the current season in which the soil was treated.Abbreviations D through drainage - DAS days after sowing of the crop on 31 May 1988 - DM dry matter produced in the above-ground portion of the crop (kg ha^–1) - E₀ evaporation from Class A pan (mm) - E_s evaporation from uncropped soil (mm) - E_sc evaporation from soil beneath the wheat canopy (mm) - ET evapotranspiration (mm) - FE fallowing efficiency (gain in soil moisture storage/rainfall) - GAI green area index (area of green vegetation per unit land area) - GWUE water-use efficiency for grain production (grain yield/total ET, kg ha^–1mm^–1) - K extinction coefficient (see equation 1) - RO run-off of moisture from soil surface during/following rainfall (mm) - SM available soil moisture (mm) at harvest (SMh) or at planting (SMp) - WUE water-use efficiency for total above-ground dry matter yield (see GWUE)     

High night temperatures during grain number determination reduce wheat and barley grain yield: a field study

Warm nights are a widespread predicted feature of climate change. This study investigated the impact of high night temperatures during the critical period for grain yield determination in wheat and barley crops under field conditions, assessing the effects on development, growth and partitioning crop‐level processes driving grain number per unit area (GN). Experiments combined: (i) two contrasting radiation and temperature environments: late sowing in 2011 and early sowing in 2013, (ii) two well‐adapted crops with similar phenology: bread wheat and two‐row malting barley and (iii) two temperature regimes: ambient and high night temperatures. The night temperature increase (ca. 3.9 °C in both crops and growing seasons) was achieved using purpose‐built heating chambers placed on the crop at 19:000 hours and removed at 7:00 hours every day from the third detectable stem node to 10 days post‐flowering. Across growing seasons and crops, the average minimum temperature during the critical period ranged from 11.2 to 17.2 °C. Wheat and barley grain yield were similarly reduced under warm nights (ca. 7% °C^?1), due to GN reductions (ca. 6% °C^?1) linked to a lower number of spikes per m². An accelerated development under high night temperatures led to a shorter critical period duration, reducing solar radiation capture with negative consequences for biomass production, GN and therefore, grain yield. The information generated could be used as a starting point to design management and/or breeding strategies to improve crop adaptation facing climate change.     

Effect of High Temperature Stress at Anthesis on Grain Yield and Biomass of Field-grown Crops of Wheat

Spring wheat (Triticum aestivumL., ‘Chablis’) wasgrown under field conditions from sowing until harvest maturity,except for a 12-d period [70–82 days after sowing (DAS)coinciding with anthesis] during which replicated crop areaswere exposed to a range of temperatures within two pairs ofpolyethylene-covered temperature gradient tunnels. At 82 DAS,an increase in mean temperature from 16 to 25 °C duringthis treatment period had no effect on above-ground biomass,but increased ear dry weight from 223 to 327 g m^-2and, at 83DAS, reduced root biomass from 141 to 63 g m^-2. Mean temperatureover the treatment period had no effect on either above-groundbiomass or grain yield at maturity. However, the number of grainsper ear at maturity declined with increasing maximum temperaturerecorded over the mid-anthesis period (76–79 DAS) and,more significantly, with maximum temperature 1 d after 50% anthesis(78 DAS). Grain yield and harvest index also declined sharplywith maximum temperature at 78 DAS. Grain yield declined by350 g m^-2at harvest maturity with a 10 °C increase in maximumtemperature at 78 DAS and was related to a 40% reduction inthe number of grains per ear. Grain yield was also negativelyrelated to thermal time accumulated above a base temperatureof 31 °C (over 8 d of the treatment from 5 d before to 2d after 50% anthesis). Thus, grain fertilization and grain setwas most sensitive to the maximum temperature at mid-anthesis.These results confirm that wheat yields would be reduced considerablyif, as modellers suggest, high temperature extremes become morefrequent as a result of increased variability in temperatureassociated with climate change.Copyright 1998 Annals of BotanyCompany Triticum aestivum, spring wheat, temperature, grain number, grain yield, root growth.     

Canonical correlation analysis of abiotic and biotic variates in insect-infested grain bulks

Summary The impact of insect infestation on several biotic and abiotic variates in 3 small bulk-wheat ecosystems was studied by measuring these variates at monthly intervals during 1969–1970. One ecosystem was insect-free, the second was artificially infested with Cryptolestes ferrugineus and Oryzaephilus surinamensis, and the third with Sitophilus granarius and Tribolium castaneum. The relationships between 8 environmental and 8 entomological and microbial variates were examined by canonical correlation analyses. The degree of predictability (R _c ² ) of the first pair of canonical variates in the 3 ecosystems ranged from 80% to 95%. The first 2 pairs of canonical variates were highly significant in all 3 analyses (P<0.01). In the insect-free ecosystems the canonical variates revealed that temperature and the period of storage were the primary environmental antecedents involved and the criterion was composed primarily of the field fungus Alternaria and the storage fungus Aspergillus. In the second ecosystem uric acid level in the grain bulk was an additional environmental factor that affected the population of both species of insects and 3 kinds of fungi Altrnaria, Aspergillus, and Penicillium. In the third ecosystem temperature, time, uric acid and moisture interacted collectively, with density of insect populations, reduction of Alternaria, and increase of Aspergillus.Contribution No. 502 from Research Station, Canada Department of Agriculture, Winnipeg, Canada. Based partly on a paper presented at the Annual Meeting of the Ecological Society of America, Chicago, Illinois, U.S.A., on 28 December, 1970.     

Ecology of fungi associated with moist stored barley grain

A study of the ecology of fungi associated with moist stored barley grain was carried out on samples from a partially sealed silo in Cumberland. Samples were collected during harvest and after storage at high moisture content in a partially sealed silo. At harvest, the field fungi Alternaria, Fusarium, Cladosporium and Mucor spp. were dominant both in the husks and in the dehusked, surface-sterilized grain but they were rapidly succeeded by the storage fungi: Aspergillus, Penicillium and Absidia spp. then constituted about 80 % of the initial invasion. At this stage internal grain infection rarely exceeded 5 % compared to 65–80 % infection in the husks. In subsequent months, there was a remarkable increase in invasion, mainly by Penicillium, Aspergillus and Absidia spp. and by yeasts, which appeared both in the husks and in dehusked grain. In the third month of storage, Penicillium cyclopium, P. roqueforti, Absidia corymbifera, Aspergillus candidus, A. terreus and yeasts became dominant. The thermophilous species Aspergillus fumigatus, A. terreus, Absidia corymbifera, Mucorpusillus and Dactylomyces crustaceus were isolated from husks and in dehusked grain incubated at 37 and 45 °C. Most grains were infected significantly by single genera.     

Strategies to reduce DON contamination of wheat with different soil tillage and variety systems

With the focus on minimizingFusarium head blight and the deoxynivalenol (DON) contamination of wheat a three year crop rotation system starting with forage maize and followed by two years of winter wheat was combined with three soil tillage systems and selected plant varieties with varying susceptibility toFusarium infection. Higher DON concentrations were generally observed in wheat grain when the soil was mulched rather than ploughed, depending on the mass of maize residues remaining on the soil surface. Maize residues are the most important source ofFusarium inoculum. Infected maize residues had a main impact on the level of DON contamination in wheat grain particularly in the first year after maize cultivation. When the maize stubble was chopped before mulching, the decomposition of the residues was speeded up and the DON contamination of the wheat grain was lower. In the second year following the maize crop, the decomposition of the maize residues/Fusarium biomass was nearly complete and the infection risk was reduced considerably. An influence of the susceptibility of the maize variety against stem rot on the DON concentration of the succeeding winter wheat crop was not observed. The less susceptible wheat variety was suitable for controlling the higher infection risk deriving from the introduction of maize in wheat rotation and the use of mulching techniques. Presented at the 28^th Mykotoxin-Workshop, Bydgoszcz, Poland, May 29–31, 2006     

The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Winter wheat (Triticum aestivum L. cv. Hereward) was grown inthe field inside polyethylene-covered tunnels at a range oftemperatures at either 380 or 684 µmol mol^–1 CO₂.Serial harvests were taken from anthesis until harvest maturity.Grain yield was reduced by warmer temperatures, but increasedby CO₂ enrichment at all temperatures. During grain-filling,individual grain dry weight was a linear function of time fromanthesis until mass maturity (attainment of maximum grain dryweight) within each plot. The rate of progress to mass maturity(the reciprocal of time to mass maturity) was a positive linearfunction of mean temperature, but was not affected by CO₂ concentration.The rate of increase in grain dry weight per ear was 2.0 mgd^–1 greater per 1 C rise, and was 8.0 mg d^–1 greaterat 684 compared with 380 µmol mol^–1 CO₂ at a giventemperature. The rate of increase in harvest index was 1.0%d^–1 in most plots at 380 µmol mol^–1 CO₂ andin open field plots, compared with 1.18% d^–1 in all plotsat 684 µmol mol^–1 CO₂. Thus, the increased rateof grain growth observed at an elevated CO₂ concentration couldbe attributed partly to a change in the partitioning of assimilatesto the grain. In contrast, the primary effect of warmer temperatureswas to shorten the duration of grain-filling. The rate of graingrowth at a given temperature and the rate of increase in harvestindex were only independent of the number of grains per earabove a critical grain number of 23–24 grains per ear({small tilde}20 000 grains m^–2). Key words: Winter wheat, grain growth, temperature, CO₂, harvest index, critical grain number     

Photosynthesis,root respiration,and grain yield of spring wheat in response to surface soil drying

The aims of this research were to test the influence of surface soil drying on photosynthesis, root respiration and grain yield of spring wheat (Triticum aestivum), and to evaluate the relationship between root respiration and grain yield. Wheat plants were grown in PVC tubes 120 cm in length and 10 cm in diameter. Three water regimes were employed: (a) all soil layers were irrigated close to field water capacity (CK); (b) upper soil layers (0–40 cm from top) drying (UD); (c) lower soil layer (80–120 cm from top) wet (LW). The results showed that although upper drying treatment maintained the highest root biomass, root respiration and photosynthesis rates at anthesis, the root respiration of the former was significantly (P < 0.05) lower than the latter at the jointing stage. There were no differences in water use efficiency or harvest index between plants from the upper drying and well-watered treatment. However, the grain weight for plants in the upper drying treatment was significantly (P< 0.05) higher than that of in well-watered control. The results suggest that reduced root respiration rate and the amount of photosynthates utilized by root respiration in early season growth may also have contributed to improve crop production under soil drying. Reduced root activity and root respiration rate, in the early growth stage, not only increased the photosynthate use efficiency (root respiration rate: photosynthesis ratio), but also grain yield. Rooting into a deeper wet soil profile before grain filling was crucial for spring wheat to achieve a successful seedling establishment and high grain yield.     

Principal component analysis of interrelations in stored-wheat ecosystems infested with multiple species of insects

Principal component analysis (PCA) was used to determine the effects of infestation of bulk stored wheat by multiple species of insects at 30±2°C for 60 wk. Eight 204-liter drums containing wheat at 15.5% moisture content were used as three distinct man-made ecosystems: (a) Control system (2 drums), insect-free; (b) RST system (3 drums), artificially infested with Rhyzopertha dominica (F.),Sitophilus oryzae (L.), and Tribolium castaneum (Herbst ); and (c) COT system (3 drums), infested with Cryptolestes ferrugineus (Stephens ),Oryzaephilus surinamensis (L.), and Tribolium castaneum. The variables measured tri-weekly within each system included carbon dioxide, oxygen, temperature, grain moisture, seed damage, grain weight and volume, dust weight and volume, fat acidity values (FAV) of the wheat, seed germination, microflora including Alternaria alternata(Fr.) Keissler ,Aspergillus glaucus group, Aspergillus candidusLink , and bacteria, insects and the mite Tarsonemus granariusLindquist . PCA provided multivariate synopsis of the data quantifying several important relationships among the variables monitored. Tri-weekly and cumulative 60-wk analyses of each system showed that high bacterial counts were associated with high FAV levels;Tarsonemus numbers were positively related to Aspergillus; Alternaria and seed germination were negatively related to FAV, bacteria and grain damage; and that the number of insects was related to the presence of Aspergillus and negatively related to the presence of bacteria. Seed germination and Alternaria infection often decrease rapidly presumably because of infection by fungi of the Aspergillus glaucus group. The combined action of R. dominica and Aspergillus spp. enhanced seed damage and increased grain moisture content thus promoting bacterial growth which in turn inhibited insect and mold growth. Fat acidity values increased with time unless seed damage and bacterial infection were extensive as in the RST system.     

The effect of rabbit (Oryctolagus cuniculus) grazing damage on the growth and yield of winter cereals

In 1986/1987 and 1987/1988 wild rabbits (Oryctolagus cuniculus) were trapped and enclosed in a 0.3 ha site in which two varieties of winter barley (Igri and Panda) and two of winter wheat (Norman and Mission) were grown in a split plot block design experiment. The level of rabbit population was varied to emulate natural variation in numbers throughout the growing season and was regulated to produce a peak density of 77 rabbits ha^-* in the first year, and 33 rabbits ha^-1! in the second year. Grazing was managed by the use of exclosure fences around plots to produce four treatment levels - protected, autumn grazed, spring grazed and totally grazed regimes. Rabbit damage was assessed using stem and leaf damage indices several times through the growth of the crops. Yields were measured in terms of head number, grain weight and total yield. There was no evidence of varietal preference among the four cereal varieties on the basis of damage assessments. In the first year the totally grazed treatment led to an increase in the number of unripe heads present at harvest which would indicate a delayed harvest date in a field crop. Winter wheat showed a trend towards higher yield loss in spring-damaged plots, possibly linked to the time of tillering in this crop. Yield losses overall were highest in those plots grazed in either the autumn or throughout the entire season. The level of peak rabbit population did not appear to influence the degree of loss in either year. The results indicate that there may be a threshold of rabbit damage early in the growth of the crop which contributes most to the yield loss. This emphasises the importance of protecting a winter cereal crop at its establishment phase.     

Soil factors affecting selenium concentration in wheat grain and the fate and speciation of Se fertilisers applied to soil

UK crops have a low selenium (Se) status, therefore Se fertilisation of wheat (Triticum aestivum L.) at 10 field sites was investigated and the effect on the content and speciation of Se in soils determined. Soil characterisation was carried out at each field site to determine the soil factors that may influence wheat grain Se concentrations in unfertilised plots. Soil samples were taken after harvest from each treatment to determine the fate and speciation of selenate fertiliser applied to soil. Wheat grain Se concentrations could be predicted from soil Se concentration and soil extractable sulphur (S) using the following regression model: Grain Se?=?a?+?b(total soil Se)?+?c(extractable soil Se) - d(extractable soil S), with 86 % of the variance being accounted for, suggesting that these properties control Se concentrations in grain from unfertilised plots. Extractable soil Se concentrations were low (2.4 – 12.4 µg kg^?1) and predominantly consisted of selenite (up to 70 % of extractable Se) and soluble organic forms, whereas selenate was below the detection limit. Little of the added Se, in either liquid or granular form was left in the soil after crop harvest. Se fertilisation up to 20 g ha^?1 did not lead to a significant Se accumulation in the soil, suggesting losses of Se unutilised by the crop.     

Association of two measures of vegetative growth rate with other traits in inter and intraspecific matings of oats

Summary F₂-derived oat lines from inter (Avena sativa L. x A. sterilis L.) and intraspecific (among A. sativa cultivars) matings were evaluated in the F₃, F₄, and F₅ generations for heading date, grain and straw yields, biomass, vegetative dry weight at anthesis, vegetative growth rates until anthesis (GRA) and until maturity (GRM), and harvest index. The associations of GRA and GRM with harvest index ranged from zero to slightly negative. The positive correlations of GRA and GRM with grain yield were stronger in inter than in intraspecific matings. Grain yield was positively associated with harvest index in both inter and intraspecific matings. The results suggest the use of A. sterilis x A. sativa matings to improve vegetative growth rate, grain yield, and, to a certain extent, harvest index simultaneously without affecting the growth duration of the crop.Journal Paper No. J 12130 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011, USA. Project No. 2447. Part of a study conducted by the senior author while he was a visiting scientist at Iowa State University     

Parasitism by Pteromalus cerealellae (Hymenoptera: Pteromalidae) on the Cowpea weevil, Callosbruchus maculatus (Coleoptera: Bruchidae): Host density, temperature effects, and host finding ability

Studies on interactions between a larval parasitoid, Pteromalus cerealellae (Boucek) and one of its hosts, Callosobruchus maculatus (F.) were carried out in the laboratory. The number of host larvae parasitized by P. cerealellae increased with host larvae at low densities and tended to a plateau at a density of 25 larvae per female parasitoid. Each parasitoid was able to parasitize more hosts and produced more offspring at 20 and 25 °C than at 30 °C. The number of non-infested seeds mixed with seeds infested with the last instar of C. maculatus did not preclude P. cerealellae from identifying infested seeds and attacking larvae inside them. When infested seeds were tightly packed, several host larvae escaped parasitism. P. cerealellae may be a useful biological control agent in newly harvested cowpea with low C. maculatus infestation, and lowering the temperature of the storage system may enhance the effectiveness of this parasitoid.     

Farm‐scale assessment of movement patterns and colonization dynamics of the grain aphid in arable crops and hedgerows

1 Integrated management of crop pests requires the identification of the appropriate spatial scale at which colonization processes occurs. We assessed, by coupling demographic and genetic methods, the relative contribution of local and transient migrants of the grain aphid Sitobion avenae to wheat field colonization in spring. 2 We examined, during two consecutive years, the daily colonization of wheat by aphid migrants and compared this with daily aphid flight monitored by a local 12.2‐m suction trap. The genetic profiles of aphids landing on crops were compared with those of both flying aphids caught by the suction trap and local populations from arable crops and hedgerows. 3 In the first year, we observed: (i) a strong correlation between aphids colonizing the crop and those moving within the crop and a close genetic similarity between aphids from these samples and (ii) a high level of genetic differentiation between these aphids and populations from local cereals and field margins. In the second year, the number of migrants recorded on the wheat was three‐fold higher than in the previous year, and less correlated with that recorded by the suction trap. This was associated with a lack of genetic differentiation between all samples. 4 This variation in the colonization processes resulted mainly in an abrupt increase in abundance of genotypes from local over‐wintering sites in 2004. This suggests that, despite the long range dispersal potential of the grain aphid, outbreak risks could be mainly determined at a local scale, encouraging the design of relatively small management units.     

Effect of delayed harvest on contamination of pearl millet grain with mycotoxin-producing fungi and mycotoxins

The response to delayed harvest of fungal and mycotoxin contamination of grain of the pearl millet hybrid HGM 100 was examined in 1992 and 1993. Samples of grain were assayed from seven plantings at locations near Tifton, Georgia, USA. Grain was harvested at 30, 40, and 50 days after anthesis and evaluated for infection byFusarium species andAspergillus flavus, and mycotoxin contamination. Mean isolation frequencies ofF. semitectum (35.6%) andF. chlamydosporum (17.2%) increased linearly with delayed harvest.Fusarium moniliforme andF. equisiti were infrequently isolated (<0.5%) and did not increase in the grain when harvest was delayed. Low mean concentrations of zearalenone (0.17 ppm), nivalenol (0.42 ppm), and deoxynivalenol (0.01 ppm) were detected but were not affected by delayed harvest. Isolation frequencies ofF. chlamydosporum andF. equiseti were correlated (P=0.07) with levels of nivalenol.Aspergillus flavus was not isolated from the grain, and aflatoxin concentrations averaged 1.9 ppb.     

Growth,development, and biomass partitioning of the perennial grain crop Thinopyrum intermedium

Intermediate wheatgrass (Thinopyrum intermedium) is a perennial grass that is being domesticated and improved for use as a grain crop. As a perennial grain crop, intermediate wheatgrass has the potential to produce economically viable, food‐grade grain while providing environmental benefits such as reduced erosion and nitrate leaching. To guide agronomic activities for this new crop, more information on intermediate wheatgrass growth and development is needed. We sampled plants every 3–5 days throughout the growing season at three environments to measure growth and development in response to accumulating growing degree days (GDD). A numerical growth index was used to quantify morphological development. Growth index, plant height, biomass, height of the tallest node, and biomass partitioning to leaf, stem, and inflorescence were modelled as a function of GDD. We predicted dates (in GDD and day of the year) for critical morphological events as they relate to grain crop production using model equations. The fraction of total biomass allocated to leaves decreased and stems increased in response to GDD, and both components represented equal proportions of aboveground biomass at plant maturity. Growth and development was similar across environments, but variation in yield components (e.g., 50 seed weight, seed mass inflorescence^?1) was observed. Our results provide the first quantification of growth and development of intermediate wheatgrass, and have application to growers seeking to determine optimal timing of agronomic practices, as well as crop modellers working to integrate new crops into simulation models. As intermediate wheatgrass expands as a perennial grain crop, growth and development should be measured in a broader range of temperature and precipitation conditions.