The Control of volunteer potatoes in the autumn in cereal stubbles.

Many of the volunteer potato plants present in two winter barley crops continued to grow after the cereal harvest. Aminotriazole applied to this regrowth resulted in 50–69% fewer potato plants emerging in the year following treatment. Glyphosate gave better control, averaging 72% in one experiment and 88% in the other. Few of the potato plants regrew after harvest of two spring barley crops and with the same two herbicides over 70% of the tubers survived. Herbicide response was not affected by dose (glyphosate 0.5-3.0 kg/ha and aminotriazole 1.5-4.0 kg/ha). With adequate time for the potatoes to start regrowing after harvest (3–4 wk), there was no improvement in performance from further delay. The potential use of these two herbicides in cereal stubbles for groundkeeper potato control is discussed     

Effects of Break Crops on Yield and Grain Protein Concentration of Barley in a Boreal Climate

Rotation with dicotyledonous crops to break cereal monoculture has proven to be beneficial to successive cereals. In two fields where the soil had been subjected to prolonged, continuous cereal production, two 3-year rotation trials were established. In the first year, faba bean, turnip rape and barley were grown, as first crops, in large blocks and their residues tilled into the soil after harvest. In the following year, barley, buckwheat, caraway, faba bean, hemp and white lupin were sown, as second crops, in each block and incorporated either at flowering stage (except barley) or after harvest. In the third year, barley was grown in all plots and its yield and grain protein concentration were determined. Mineral N in the plough layer was determined two months after incorporation of crops and again before sowing barley in the following year. The effect of faba bean and turnip rape on improving barley yields and grain protein concentration was still detectable two years after they were grown. The yield response of barley was not sensitive to the growth stage of second crops when they were incorporated, but was to different second crops, showing clear benefits averaging 6-7% after white lupin, faba bean and hemp but no benefit from caraway or buckwheat. The effect of increased N in the plough layer derived from rotation crops on barley yields was minor. Incorporation of plants at flowering stage slightly increased third-year barley grain protein concentration but posed a great potential for N loss compared with incorporation of crop residues after harvest, showing the value of either delayed incorporation or using catch crops.     

Persistence of Genetically Modified Potatoes in the Field

Volunteers from genetically modified (GM) potatoes may pose an environmental problem if allowed to grow in the field after the annual crop is harvested. We tested whether they are more likely to produce volunteers than non-GM potatoes. Specifically, we compared the number of volunteers, number of tubers per plant, tuber size, and their vertical distribution in the soil. More volunteer plants came from non-GM potatoes than from GM potatoes, but the number and size of tubers were similar between the two. Vertical distribution of the tubers differed significantly, with most non-GM tubers being found in shallower soil (<2 cm deep). Our results suggest that spontaneous GM volunteers may emerge and produce tubers to a degree similar to that of the non-GM plants. No viable volunteers emerged from GM tubers in the next growing season, probably deterred by winter frost and a period of low soil temperatures (below −2°C) at our study site. However, in regions with warmer climates, such GM volunteers may survive Winter and produce more plants the following year.     

The biology, ecology, and harmfulness of the flea-beetle Chaetocnema aridula Gill (Coleoptera, Chrysomelidae) in the forest-steppe of the middle Volga Area

In the forest-steppe of Samara Province, Chaetocnema aridula Gill. dominates among all the species of Chaetocnema Steph. found in cereal crops. The species develops mainly on winter wheat, and, to a lesser extent, on spring wheat and barley. In autumn, adult beetles aggregate on millet for pre-hibernation feeding. The highest population density of Ch. aridula was observed in the humid and warm 1997 and the lowest one, in the extremely dry 1998. In late April-the first third of May, adults begin oviposition after wintering. Larvae appear in winter and spring wheat in mid-May and in late May-early June, respectively. Larvae pupate in winter wheat, beginning from mid-June; in spring crops, pupation begins in mid-June. Adults of a new generation emerge between the middle of June and the middle of July. In spring crops, development of Ch. aridula finishes 2–3 weeks later than in winter crops. Larvae penetrate shoots in the upper soil level in the tillering zone. 50–80% of wheat and barley plants are damaged by larvae. In damaged plants, the number of shoots increases by 1.2–5.8 times, and the number of productive shoots decreases to 17–68%. In plants damaged by flea-beetles, harvest losses constitute 62–90% and 5–20% in winter and spring wheat crops, respectively, and the total harvest loss constitutes 0.3–3.9 and 1–15%, respectively.     

The effect of three herbicides on the number of spores of Rhynchosporium secalis on barley stubble and volunteer plants

Single sprays of paraquat, glyphosate or dinoseb-in-oil, were applied to barley stubble or volunteer plants and their effects on the number of spores of Rhynchosporium secalis were studied weekly. Spore concentrations were measured by washing samples of stubble or volunteer plants and counting spores using a haemocytometer. The number of spores recovered from stubbles was relatively small; both paraquat and glyphosate caused some reductions but the results were not consistent. Treatment with paraquat generally caused a transitory increase on volunteer plants; this effect was not found after glyphosate. Both herbicides caused persisting reductions from 4 wk after treatment. Volunteer plants treated with dinoseb-in-oil had fewer spores for 6 wk after treatment, but the plants were not killed and when new growth became infected, spore production recovered to equal that on untreated plants. The fungicide captafol caused some reductions in spore number on stubble but results were not consistent, applied after paraquat it had no effect. It was generally ineffective when applied to volunteer plants; applied after paraquat it tended to increase spore number, but the differences were seldom significant. Spores washed from volunteer plants treated with paraquat or glyphosate were inoculated to pot-grown barley seedlings; neither herbicide had any effect on spore viability. Viable spores were recovered in February from stubble or volunteer plants treated the previous autumn with paraquat or glyphosate respectively.     

The fate of residual 15N-labelled fertilizer in arable soils: its availability to subsequent crops and retention in soil

An earlier paper (Macdonald et al., 1997; J. Agric. Sci. (Cambridge) 129, 125) presented data from a series of field experiments in which ¹⁵N-labelled fertilizers were applied in spring to winter wheat, winter oilseed rape, potatoes, sugar beet and spring beans grown on four different soils in SE England. Part of this N was retained in the soil and some remained in crop residues on the soil surface when the crop was harvested. In all cases the majority of this labelled N remained in organic form. In the present paper we describe experiments designed to follow the fate of this `residual' <sup>15</sup>N over the next 2 years (termed the first and second residual years) and measure its value to subsequent cereal crops. Averaging over all of the initial crops and soils, 6.3% of this `residual' ¹⁵N was taken up during the first residual year when the following crop was winter wheat and significantly less (5.5%) if it was spring barley. In the second year after the original application, a further 2.1% was recovered, this time by winter barley. Labelled N remaining after potatoes and sugar beet was more available to the first residual crop than that remaining after oilseed rape or winter wheat. By the second residual year, this difference had almost disappeared. The availability to subsequent crops of the labelled N remaining in or on the soil at harvest of the application year decreased in the order: silty clay loam>sandy loam>chalky loam>heavy clay. In most cases, only a small proportion of the residual fertilizer N available for plant uptake was recovered by the subsequent crop, indicating poor synchrony between the mineralization of ¹⁵N-labelled organic residues and crop N uptake. Averaging over all soils and crops, 22% of the labelled N applied as fertilizer was lost (i.e., unaccounted for in harvested crop and soil to a depth of 100 cm) by harvest in the year of application, rising to 34% at harvest of the first residual year and to 35% in the second residual year. In the first residual year, losses of labelled N were much greater after spring beans than after any of the other crops.     

Overwintering locations and hosts for onion thrips (Thysanoptera: Thripidae) in the onion cropping ecosystem in New York

Identifying locations where onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), overwinter and subsequently disperse is important for designing control strategies. In upstate New York from 2003 through 2006, potential overwintering sites in the commercial onion, Allium cepa L., cropping system were investigated early in the spring before onion seedling emergence and again late in the season after onions were harvested. Onion thrips adults were sampled directly from the soil and indirectly from the soil by using emergence cages. Sampling locations included onion field interiors and edges and areas outside of these fields, including woods. Host material sampled included onion culls; volunteer onions, which sprout from cull onions left behind after harvest; and weeds. Onion thrips adults were found in all sections of onion fields and in locations outside of onion fields, with the fewest emerging from woods. Emergence began in early May and extended into June. Peak emergence occurred during the last half of May, at which time 50-75% of the population had emerged. Adults colonized volunteer onions as early as late March and as late as mid-November. No adults were found overwintering in onion cull piles. Adults also colonized several weed species, especially pigweed, Amaranthus hybridis L., and lambsquarters, Chenopodium album L., late in the fall. Our results indicate that onion thrips adults overwinter in the soil within and near onion fields and that they probably colonize volunteer onion plants before subsequent generations infest the onion crop in the spring. Volunteer onions and weeds also provide onion thrips with a host after onions are harvested. Consequently, onion thrips management strategies should include tactics that reduce volunteer onion and weed abundance.     

Root responses to cereal cyst nematode (Heterodera avenae) in hosts with different resistance genes

The development of cereal cyst nematode (CCN; Heterodera avenae ) induced syncytia in the host roots of infected resistant bread wheat ( Triticum aestivum cv. AUS10894), diploid wheat ( Aegilops tauschii ), barley ( Hordeum vulgare cv. Chebec and cv. Galleon) and in the susceptible wheat cv. Meering and barley cv. Clipper were studied over a period of 13 d. The resistance to CCN in these cereal plants is conferred by the resistance genes Cre1 in the wheat cv. AUS10894, Cre3 in A. tauschii , Ha2 in barley cv. Chebec and Ha4 in barley cv. Galleon. Anatomical observations were made on the development of the syncytia in CCN-infected wheat and barley roots, which carry each of these four sources of resistance genes. Accelerated development of the syncytia in resistant plants, especially in the barley cultivars, was observed. The sites of syncytia development in susceptible wheat and barley were also closely associated with the vascular tissues in the stele, but less so in the resistant plants. The syncytia in the infected susceptible wheat and barley were also metabolically active at day 13. By contrast, the syncytia of resistant wheat plants carrying the Cre1 or Cre3 genes remained extensively vacuolated and less metabolically active. In barley plants with the Ha2 or Ha4 genes, the syncytia appeared non-functional and in early stages of degeneration by day 13 after inoculation.     

Treating potato ridges in spring with aldicarb, D-D or dazomet to control potato cyst-nematode, Heterodera rostochiensis, in sandy clay and peat loam soils

Applied to potato ridge soil in spring, before potatoes were planted, small amounts of aldicarb (10-3 kg/ha or less) controlled potato cyst-nematodes (Heterodera rostochiensis Woll.) better than large amounts of dazomet (110–466 kg/ha) or D-D (102–439 kg/ha). Applied in spring 1968 and 1969 to heavily infested sandy clay soil 466 kg dazomet/ha allowed Majestic potatoes to grow and yield well in both years without increasing the number of nematodes in the soil after harvest, but in peaty loam dazomet was toxic to potato plants and, when applied in autumn, killed fewer nematodes. D-D in potato ridges in spring controlled nematodes less well than dazomet or aldicarb, but 896 kg D-D/ha injected in sandy clay soil in autumn increased potato yield the following year without increasing the number of nematodes after harvest.     

A genetic playground for enhancing grain number in cereals

Improving the yield stability of cereal crops with a view to bolstering global food security is an important priority. The components of final grain number per plant at harvest are determined by fertile spikes per plant, number of fertile spikelets per spike and number of grains per spikelet. In this review article, we focus on the genetic factors of floral development and inflorescence architecture known to influence grain number and provide a broad overview of genes and genetic pathways that potentially can be manipulated to increase the yield of cereal crops, in particular wheat (Triticum aestivum) and barley (Hordeum vulgare). In addition, we discuss the outcome of multidisciplinary genomics knowledge to identify potential gene targets to develop conceptual ideotypes to meet the future demand.     

Earlier onset of DNA fragmentation in leaves of wheat compared to barley and rye

We have found extensive nucleosomal fragmentation of native DNA extracted from leaves of healthy cereal plants, as indicated by ladder patterns on agarose gels and TUNEL staining. The time of first appearance of fragmentation differed among cereals. Native DNA from the first leaf of 10-day-old plants formed a clear ladder pattern of multiples of 180 bp fragments in wheat and triticale but not in barley and oats. In one cultivar of rye a weak ladder pattern occurred but not in another. Freezing and thawing of samples before DNA extraction resulted in much more extensive DNA fragmentation in wheat but not in rye and barley, indicating that DNA-degrading enzymes are present in the cytoplasm of wheat, but not in barley and rye, at this stage. In barley, nucleosomal fragmentation was first detected in 25-day-old plants. These results indicate that programmed cell death takes place in developing leaves of young cereal plants, but that the time of onset differs among cereal species.     

A role for ethylene in barley plants responding to soil water shortage

The influence of water shortage and ethylene (ethephon) application on ear fertility and tillering of barley plants were compared. In both cases, highest sensitivity was observed during jointing and pre-anthesis (Feekes 7–9). The ear initial with the surrounding tissue was identified as the site of ethylene action. Treating this region of barley plants with AVG before wilting partly prevented drought effects. These results, in connection with rising ethylene values in ear-bearing stem segments of wilting barley plants (more obvious in increasing ACC and MACC levels), especially in the drought-sensitive stages, favors a role for ethylene in the development of cereal plants under drought.     

Phenological and demographic behaviour of an exotic invasive weed in agroecosystems

An experimental work was conducted in Lleida (Spain) aiming to characterise the phenology and to quantify the demographic processes regulating the populations of Abutilon theophrasti Medicus in maize fields. Seedling emergence started a few days after crop sowing in early May and continued during two more months. The vegetative phase was very long due to the late seeding emergence; these later emerged plants showed a slower development, and many of them did not reach the fertility stage. A flowering peak was observed 12 weeks after emergence in late July, and fruit dehiscence and seed setting started in mid August, several weeks before crop harvest. Four different cohorts were identified, and two main peaks of emergence were determined 21 and 49 days after crop sowing nearest related with field irrigation. A functional logarithmic relationship between cumulative growing degree-days (GDD) and cumulative emergence was also described. The resulting demographic diagram reflects greater values relating to seedling survival for May cohorts (90.2 vs 7.9%), to fertility (100 vs 75%) and to fecundity (3774 vs 92 seeds pl⁻¹) than those determined for the June cohorts. The late emerged plants are subjected to a high density and are strongly affected by light competition, and their reproductive phase initiation delay is of about 10–20 days. In an assay conducted in Petri dishes, the seeds provided from plants emerged earlier were found more vigorous and germinated more than those from late emerged plants, which seem to be affected by incomplete fruit and seed ripening. Following the crop cycle without any weed control, the population rate increase was about 21.2. These values explain the high invasion capacity of this weed in the local summer irrigated fields, which consists in assuring their presence through a persistent soil seed bank and increasing the probability to spread to other fields. This revised version was published online in July 2006 with corrections to the Cover Date.     

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

The tolerance of spring and winter cultivars of wheat, barley and oats to infection by barley yellow dwarf virus (BYDV) was examined in field tests. Sererely affected plants were stunted and grain yields were considerably reduced. These changes in infected spring barley cultivars were associated with decreases in both ear length and number and sizes of grain. Most barley and oat cultivars were more susceptible than wheat cultivars. Yield losses decreased with successively later dates of inocultaiton, the yield response being characteristic of the tolerance of individual cultivars. Differences between tolerant and susceptible cultivars were insignificant in most cases where infection occurred after growth stage 7. Individual seedling symptoms assessed in April and May were more closely related to each other and to yield losses than those recorded in March and June. The incorporation of seedling symptoms into indices of infection permits estimates of decrease in yield to be made by applying the formulae, DY = (LC+LA+SH)/3 to barley cultivars and DY = 1.7 × (LC+LA+SH)/3 - 7 to oat cultivars. Thus decreases in grain yield (DY) can be related to decreases in seedling height (SH) and increases in percentage of leaf area discoloured (LA) and intensity of discoloration (LC). Plot symptoms of infection, scored on a 0–7 scale, offered a more convenient method of assessment than individual seedling symptoms. Plot scores (PA) were closely correlated with other seedling symptoms and with decreases in grain yield (DY), and can thus be used to estimate yield losses by substituting into the formula, DY = 14PA (April)-8. This formula was found to be applicable to all cereal cultivars examined in N.I.A.B. trials, there being no distinction between wheat, barley and oats.     

Occurrence of barley yellow dwarf virus (BYDV) isolates in different farmland habitats in western France and south-west England

The incidence and distribution of the three principal isolates of barley yellow dwarf virus (PAV, RPV and MAV) are described in winter cereal crops, cereal (stubble) regrowth and grasses from 11 sites in western France and south-west England during 1987 and 1988. Isolates were identified by indirect ‘sandwich’ ELISA using the monoclonal antibodies MAC91, MAC92 and MAFF2. More virus infection occurred in all localities and in most of the plant communities sampled, with the exception of perennial grass leys, in 1987 than in 1988. All three isolates were widespread. MAV was associated more with sites further north and PAV more with those further south. The geographical distribution of RPV was less variable. Underlying these trends, the relative abundance of isolates differed considerably between habitats. RPV always predominated in perennial grass leys and MAV in most cereal crops, although in the latter MAV was less prevalent in 1987 than in 1988. The greatest regional difference was found in stubble regrowth where PAV predominated in France but MAV predominated in England. Grasses from field margins (only sampled in England) were mainly infected by MAV and RPV. The implications of these findings for the epidemiology of BYDV are discussed, especially the roles of different host plant communities or habitats in the annual infection cycle of small-grain cereals.     

Concentration of ergosterol in small-grained naturally contaminated and inoculated cereals

Ergosterol (ERG) is a major sterol constituent of most fungi. Its concentration is negligible in higher plants, but can be used as a chemical marker of the presence of fungal contaminations. In this study, ERG concentration was assessed in randomly collected samples of naturally contaminated grain (wheat, barley and oat) and in samples of grain (wheat, barley, triticale and oat) harvested after inoculation of heads with conidia of different Fusarium species. Wheat samples were analysed at three stages of grain development. The lowest ERG concentration was found in non-inoculated samples at the first stage of grain development. This concentration was increasing with grain ripening. In naturally contaminated samples collected after harvest, ERG concentration was lower in wheat than in barley and oat. ERG concentrations in inoculated samples varied significantly, but were always significantly higher than in naturally contaminated samples. In the above cereal samples it was much lower than the levels assayed in laboratory cultures inoculated with fungi from genus Fusarium. The content of ERG was also analyzed in milling products of small-grained cereals and other foodstuffs, where a considerable variation was observed. The lowest ERG amounts were assayed in flours with a high degree of purification, while the highest ones in case of flours and products with a low purification rate. The results indicate the potential application of HPLC combined with microwave-assisted extraction both when assaying samples with low ERG concentrations (naturally contaminated) and those characterized with high contents of fungal biomass (strongly infected, artificially inoculated). It also facilitates analyses of fungal biomass in technological processes, where results may be expected to vary considerably.     

Cytoplasmic DNA variation and relationships in cereal genomes

Summary Chloroplast (cp) and mitochondrial (mt) DNAs were isolated from four cereal genomes (cultivated wheat, rye, barley and oats) and compared by restriction nuclease analysis. Cleavage of cp and mt DNAs by Sal I, Kpn I, Xho I and EcoR I enzymes indicated that each cereal group contains specific cytoplasmic DNAs. A phylogenetic tree of cereal evolution has been obtained on the basis of cp DNA homologies. It is suggested that wheat and rye diverged after their common ancestor had diverged from the ancestor of barley. This was preceded by the divergence of the common ancestor of wheat, rye and barley and the ancestor of oats.The molecular weight of the different cp DNAs was determined from the Sal I and Kpn I patterns. cp DNAs from wheat, rye, barley and oats appeared to be characterized by a very similar molecular weight of about 80–82.10⁶ d.In the case of the mt DNAs, the great number of restriction fragments obtained with the restriction enzymes used prevented precise comparisons and determination of molecular weights.     

The effect of auxin on plant regeneration of wheat,barley and triticale

One of the basic components of a medium influencing somatic embryogenesis of cereals from immature embryos is the type of auxin. According to some researchers, phytohormones can also play an important role during Agrobacterium-mediated transformation. In this first part of research, the influence of three types of auxins used alone or in combination of two on somatic embryogenesis and plant regeneration in three cereal species has been tested. Eight cultivars of barley, five cultivars of wheat and three cultivars of triticale have been used. Efficiency of plant development on two regeneration media, with and without growth regulators has been compared. Efficiency of regeneration characterized by frequency of explants that form embryogenic callus ranged from 25% for wheat cultivar Torka to 100% for two barley cultivars. Mean number of plantlets regenerating per explant differed significantly (from 2 to 58) depending on the type of auxin in inducing media, the type of regenerating media as well as cultivar. The biggest differences in regeneration efficiency were observed between barley cultivars, however regeneration of plants occurred in all combinations tested. The best regeneration coefficients for most barley cultivars were obtained after culture on dicamba or dicamba with 2,4-D. However, in the case of highly regenerating cv Scarlett, the most effective culture media contained picloram or 2,4-D alone. The highest values of regeneration coefficients for two triticale cultivars (Wanad and Kargo) were obtained on picloram (26.1 and 21.4, respectively) and for `Gabo' on picloram with dicamba (12.6). The range of mean number of regenerated plantlets was from 12 to 30. Dicamba alone or lower concentrations of picloram with 2,4-D were the best media influencing embryogenic callus formation in five wheat cultivars. However, the highest values of regeneration coefficients ranging from 10.6 to 26.8 were obtained at lower concentrations of picloram with 2,4-D or picloram with dicamba. R2 regeneration medium containing growth regulators was significantly better for plantlet development in several combinations (cultivar and induction medium) than the one without growth regulators. Generally, regeneration coefficients for all tested cultivars of three cereal species on the best media were high, ranging from 5.5 for barley cultivar Rodion to 51.6 for another barley cultivar Scarlett. Plantlets developed normally, flowering and setting seed.     

Size asymmetry in intraspecific competition and the density-dependence of inbreeding depression in a natural plant population: a case study in cassava (Manihot esculenta Crantz, Euphorbiaceae)

The effects of competition on the genetic composition of natural populations are not well understood. We combined demography and molecular genetics to study how intraspecific competition affects microevolution in cohorts of volunteer plants of cassava (Manihot esculenta) originating from seeds in slash-and-burn fields of Palikur Amerindians in French Guiana. In this clonally propagated crop, genotypic diversity is enhanced by the incorporation of volunteer plants into farmers' stocks of clonal propagules. Mortality of volunteer plants was density-dependent. Furthermore, the size asymmetry of intraspecific competition increased with local clustering of plants. Size of plants was correlated with their multilocus heterozygosity, and stronger size-dependence of survival in clusters of plants, compared with solitary plants, increased the magnitude of inbreeding depression when competition was severe. The density-dependence of inbreeding depression of volunteer plants helps explain the high heterozygosity of volunteers that survive to harvest time and thus become candidates for clonal propagation. This effect could help favour the maintenance of sex in this 'vegetatively' propagated crop plant.