Studies of the cereal cyst-nematode, Heterodera avenae under continuous cereals, 1974–1978. I. Plant growth and nematode multiplication

Population changes of Heterodera avenae and crop growth in a sandy loam soil were studied from 1974 until 1978; the nematode decreased plant growth but failed in two of the years to multiply on susceptible hosts. Spring oats were the most heavily invaded cereal and produced the smallest shoots. Second-stage juveniles invaded cereal roots in decreasing numbers: spring oats > autumn oats > spring barley > spring wheat > autumn barley > autumn wheat. Numbers of females developing on the different cultivars were in a similar order. Most females developed on roots in 1976 despite poor crop growth in the severe drought. Numbers of H. avenae in soil treated with oxamyl (Vydate) at 8.8 kg/ha a. i. were less in all years except 1975. In the dry winter and spring of 1975/76 nematode multiplication was prevented in soil treated with oxamyl before drilling in the autumn. In all years large numbers of females were produced on the roots of all cultivars but in 1975 and 1978 nematode populations declined because few females survived to form cysts containing eggs and their fecundity was reduced. Numbers of cysts after harvest were not affected by formalin (38% formaldehyde) applied as a drench at 3000 litres/ha in 1977 but fecundity doubled in treated soil, and nematode multiplication increased from 3.8 × in untreated plots to 18.6 ×. When the plots were irrigated in 1978 numbers of cysts and fecundity increased in formalin treated soil resulting in an increase in multiplication from 0.3 × to 14.6 ×. Fungal parasites attacking H. avenae females and eggs are considered responsible for the poor multiplication of the nematode.     

The invasion of root tips of cereals by the cereal cyst nematode Heterodera avenue

Newly germinated seedlings of susceptible cultivars of oats, wheat, barley and rye were inoculated with second-stage juveniles of Heterodera avenae in pots of sand. Subsequent examination showed oat root tips to be more commonly invaded, and by a greater range of nematode numbers than the other cereals. A comparison of oats and barley showed that lower nematode numbers in barley were not due to a higher emigration from barley; invasion, establishment and emigration by nematodes all being greater in oats. Second-stage juveniles were more likely to migrate prior to establishment in barley than in oats.     

Morphological plasticity of wheat and barley roots in response to spatial variation in soil strength

Root systems of individual crop plants may encounter large variations in mechanical impedance to root penetration. Split-root experiments were conducted to compare the effects of spatial variation in soil strength on the morphological plasticity of wheat and barley roots, and its relationship to shoot growth. Plants of spring barley (Hordeum vulgare cv Prisma) and spring wheat (Triticum aestivum cv Alexandria) were grown for 12 days with their seminal roots divided between two halves of a cylinder packed with sandy loam soil. Three treatment combinations were imposed: loose soil where both halves of the cylinder were packed to 1.1 g cm^–3 (penetrometer resistance 0.3 MPa), dense soil where both halves were packed to 1.4 g cm^–3 (penetrometer resistance 1 MPa), and a split-root treatment where one half was packed to 1.1 and the other to 1.4 g cm^–3. In barley, uniform high soil strength restricted the extension of main seminal root axes more than laterals. In the split-root treatment, the length of laterals and the dry weight of main axes and laterals were increased in the loose soil half and reduced in the dense soil half compared with their respective loose and dense-soil controls. No such compensatory adjustments between main axis and laterals and between individual seminal roots were found in wheat. Variation in soil strength had no effect on the density of lateral roots (number per unit main axis length) in either barley or wheat. The nature and extent of wheat root plasticity in response to variation in soil strength was very different from that in response to changes in N-supply in previous experiments. In spite of the compensatory adjustments in growth between individual seminal roots of barley, the growth of barley shoots, as in wheat, was reduced when part of the root system was in compacted soil.     

The effect of barley yellow dwarf virus on field populations of the cereal aphids, Sitobion avenae and Metopolophium dirhodum

The numbers of cereal aphids, especially Metopolophium dirhodum in 1979, and Sitobion avenae in 1980, were significantly increased on BYDV infected wheat and oats in 1979, and wheat, barley and oats in 1980. The differences were probably caused by attraction of alates of each species to virus infected plants which had changed colour as a result of their infection. Significantly more alates of M. dirhodum were found on virus infected oats in 1979, and of S. avenae on oats and barley in 1980, although not on wheat in either year. probably because the colour contrast in wheat was less intense than in the other crops. Flight chamber experiments with alates of both species confirmed their visual attraction to virus-infected leaves. The interaction between virus, vector and host plants is discussed with reference to the ecology of virus spread.     

Physiological responses of apple fruits to oxygen concentrations

In experiments applying water regimes ranging from one eighth to twice the recorded average rainfall to six soils (two light sands and four silty clay loams) consistent positive correlations were found between rainfall and (a) the growth of foliage and roots of spring barley and spring oats, (b) the number of larvae which invaded the root system, (c) the number of immature females in July, and (d) the incidence of the fungus Verticillium chlamydosporium, an egg parasite of H. avenae. Final cyst numbers were sometimes lower than the number of immature females, probably because the latter were destroyed by the ‘Entomophthora-like’ fungus (Kerry & Crump 1977). Final populations of cysts and eggs were not always proportional to the number of larvae in root systems (even when the proportion of males was constant) but appeared more likely to be so in light sandy soils.     

Survival and duration of development of Oscinella spp. (Diptera: Chloropidae) on different Gramineae in the laboratory

The duration of development and survival of Oscinella frit, O. nitidissima and O. nigerrima at different growth stages of several plant species was investigated in the laboratory. The effect of the infestation on the growth of plants was also quantified. Survival of O. frit larvae was significantly lower (P < 0.01) on barley than on either oats or wheat, between which there was no significant difference. Survival was usually highest when plants were infested at the two-leaf stage and lowest when plants were infested at the five-leaf stage. The duration of development of both male and female O. frit was longer on barley than on either oats or wheat and generally increased when older plants were infested. The proportion of male flies was greatest when older plants were infested. Duration of development and survival of O. frit was similar on oats and Lolium multiflorum, but larvae did not survive on Dactylis glomerata. Of the other Oscinella species, O. nitidissima larvae did not survive on oats, wheat and barley and O. nigerrima larvae did not survive on either oats or barley. The main shoots of cereal plants infested at the two-, three- or four-leaf stages were rapidly killed by O. frit larvae whereas many of those infested at the five-leaf stage continued to grow slowly. In response to attack proportionately more tillers were produced by oat plants than by either wheat or barley plants. When cereals were infested with O. nigerrima larvae the central shoots were damaged, but most recovered and continued to grow. Damage symptoms were most obvious when cereals were infested at the two-leaf stage, oats being more severely affected than either wheat or barley.     

Functional xylem anatomy in root-shoot junctions of six cereal species

In cereals, the formation of safety zones in the root-shoot junction could protect the vessels of roots from embolism originating in the shoot. The root-shoot junction was examined both anatomically, with a light microscope, and experimentally, using a pressurized-air method, in the base of seminal and adventitious roots of maize (Zea mays L. cv. Seneca 60-II), a corngrass mutation of maize (Cg mutant), sorghum (Sorghum bicolor L. cv. Ho-Pak), winter oats (Avena sativa L. cv. Ogle), spring wheat (Triticum aestivum L. cv. Glenlea), winter wheat (T. aestivum cv. Monopol), winter barley (Hordeum vulgare L. cv. Wysor), spring rye (Secale cereale L. cv. JO-02 Finland), and winter rye (S. cereale cv. Musketeer). Two types of hydraulic architecture were found in the cereal roots: (i) a very safe root vessel system, as in winter rye, in which the vessels of the roots are separated from those of the shoots by tracheids, versus (ii) a completely unsafe system, as in corngrass, where the vessels in the root are continuous with the vessels in the shoot. The xylem anatomy of the seminal roots is generally correlated with the species-specific overall root morphology. Rye, wheat and barley, which develop four to six seminal roots, show a high degree of vascular segmentation resulting in, the formation of safe root vessels; maize, sorghum and oats, which typically develop a primary seminal root, contain unsafe vessels that are continuous through the mesocotyl and through the first node. In adventitious roots, vascular segmentation is not related to overall root morphology. Differences in the proportion of safe adventitious roots in which all the vessels end in the root-shoot junction range from 9 to 98% in the cereals studied. In the unsafe roots of these cereals, the number of vessels per root that are continuous through the junction range from 1 to 14. As significant differences in vascular segmentation of the root-shoot junction occur not only between species, but also between cultivars, we suggest that selection based on the occurrence of safety zones might be used in breeding programs designed to improve adaptation of cereals to drought and cold temperatures.This research project was supported by the Natural Sciences and Engineering Research Council of Canada through an International Scientific Exchange Award to R.A. and Dr. C.A. Peterson, and through an Operating Grant to M.G. We thank Dr. G. McLeod (Agriculture Canada, Swift Current, Sask., Canada), Dr. N.P.A. Huner (University of Western Ontario, London, Ont., Canada) and Dr. W.F. Tracy (University of Wisconsin, Madison, USA) for providing seeds; Dr. C.A. Peterson and Dr. W.B. McKendrick (University of Waterloo) for use of the Zeiss photomicroscopes; Dr. M.A. Dixon (University of Guelph, Guelph, Ont.) for use of the Moore pressure gauge; and Dr. R.J. O'Hara-Hines (University of Waterloo) for statistical advice.     

Interaction between barley yellow dwarf virus and rust in wheat, barley and oats, and the effects on grain yield and quality

In three separate experiments, the upper leaf surface of the fifth formed leaf of wheat cv. Highbury, the fourth and fifth leaves of barley cv. Julia and the third and fourth leaves of oat cv. Mostyn were inoculated in a spore settling tower with wheat brown rust (Puccinia recondita f. sp. tritici), barley brown rust (P. hordei) or oat crown rust (P. coronata f. sp. avenae), respectively. Fewer pustules developed on distal portions of leaves of plants infected with barley yellow dwarf virus (BYDV) than on similar portions of leaves from virus-free plants. There were no significant differences in the number of pustules on proximal leaf portions. In barley and oats, the number of pustules on distal leaf portions was negatively correlated with the amount of yellowing of the leaf areas scored. In wheat, symptoms of BYDV were mild and leaves were little affected by yellowing. The latent period of rust on wheat and oats was not affected by BYDV. In barley, BYDV reduced the latent period of rust on leaf 5, but not on leaf 4, and reduced it on proximal, but not distal, leaf portions. In other experiments, BYDV reduced the yield of wheat and oats by 44% and 66%, respectively, while BYDV-infected barley was almost sterile. The appropriate rust reduced the yield of wheat, barley and oats by 33%, 13% and 86%, respectively. When infected with both BYDV and rust, yield of wheat and oats was reduced by 63% and 91%, respectively. Neither BYDV nor rust affected the percentage crude protein content of wheat grain, nor did rust affect that of barley. In oats, BYDV and rust each significantly increased crude protein of grain, but rust infection of BYDV-infected plants tended to reduce it.     

Effects of long-term barley monoculture on plant-affecting soil microbiota

Effects of soil microbiota on shoot and root growth of barley were tested in a greenhouse tube-growing system. Tubes were filled with a mixture of pure sand and various percentages of soils sampled from plots in three long-term field experiments measuring effects of various crop rotations on yield. Using 3% soil in the sand-soil mixture, shoot dry weight of barley test plants was reduced by about 35% and root depth by about 40% in soils from monoculture plots as compared to soils from crop-rotation plots. Typical root symptoms on poorly growing barley plants started as distinct dark-brown zones which then rapidly spread over the whole root system until the root tips ceased to grow. As tested in one experiment, the barley monoculture soil also affected wheat and oats, but to a lesser degree than it did barley. Most of the depressing effects of monoculture soil on barley were eliminated when soil samples were treated with metalaxyl or heated to 65°C for 2 hours. A Pythium sp. frequently isolated from barley roots showing typical symptoms affected barley, wheat and oats in the same way as did barley monoculture soil.     

The rhizosphere microflora of wheat grown under controlled conditions II. Influence of the stage of growth of the plant,soil fertility and leaf treatment with urea on the rhizosphere soil microflora

Summary The rhizosphere effect of seminal roots of seedlings and of nodal roots of tillering plants of spring wheat ‘Kaspar’ was investigated under controlled conditions. The total number of micro-organisms recorded in the rhizosphere soil were significantly higher than for the non-rooted soil when investigated with the soil dilution plate method, but lower when fluorescence microscopy was used. Additions of inorganic fertilizer (NPK) decreased their numbers especially in rhizosphere soil of seminal roots and in non-rhizosphere soil, but did not change the ratio between bacteria and actinomycetes (B/A). In the rhizosphere soil the B/A ratio was higher than in the non-rhizosphere soil. An effect of urea leaf treatment was found with the dilution-plate method only in the rhizosphere soil of nodal roots, 3 to 7 days after the first treatment. Increased numbers of actinomycetes were found in this period in NPK fertilized soil, whereas increased numbers of bacteria were found at both fertility levels.     

Bionomics of aphids reared on cereals and some Gramineae

In controlled temperature, light and relative humidity, Metopolophium dirhodum and Sitobion avenae multiplied more on young Proctor barley than on Blenda oats, and less on Cappelle wheat. Rhopalosiphum padi increased in number fastest on barley and slowest on oats. More survived, and generation lengths seemed shorter, on barley for M. dirhodum and S. avenae and on wheat for R. padi. Tests with young cereals outdoors generally agreed with those in controlled conditions. On mature plants, there were more M. dirhodum on barley, more R. padi on wheat and more S. avenae on oats than on the other cereals. Given a free choice in large cages outdoors, most aphids were found on barley. When allowed to choose between grasses, more M. dirhodum were on Dactylis glomerata, Poa pratensis and Festuca pratensis, more R. padi on Lolium perenne and F. pratensis, and more S. avenae on D. glomerata and L. perenne. Most aphids of all species combined were on F. pratensis, Lolium and Phleum, and fewest on Festuca rubra and Holcus mollis.     

Distribution of aphids in cereal crops

Cereal crops were examined weekly for aphids during 1969. Plants in twenty samples of row 0.3 m long were examined in a sheltered perimeter of a crop and along a transect 36.6 m into the crop. Aphids were usually first found within 1–4 weeks of the first alatae caught in a suction trap operating 12.2 m above ground. When first alatae caught in a suction trap operating 12.2 m above ground. When the first found from 10 to 27% of the 0.3 m lengths sampled contained aphids. Rhopalosiphum padi, first found late in May, were scarce (< 0.53/0.3 m) throughout June and July. Sitobium spp. and Metapolophium dirhodum, which appeared in mid-June, were more numerous than R. padi; most occurred during the second half of July, and populations decreased just before harvest in early August. Sitobium avenae was more abundant (max. 19.3/sample) than either S. fragariae (0.91) or M. dirhodum (2.51). More aphids occurred in oats (max. 52/0.3 m) during July than in wheat (45), and barley had fewer (6.8). S. avanae was more abundant than M. dirhodum in sheltered areas of barley and wheat, and in exposed areas of the same crop M. dirhodum was commonest. Along sheltered perimeters, the ratio of S. avenae to M. dirhodum was largest in barley (11:1), intermediate in oats (6:1) and smallest in wheat (3.7:1). Sitobium spp. were most numerous on the ears, when most M. dirhodum were on the leaves. Regression analyses of log. S² on log. m suggested that S. avenae was more evenly distributed within (36.6 m) the field (b = 1.056 + 0.109) than along the sheltered perimeter (b = 1.432 + 0.132), though it seemed similarly distributed along perimeters of barley, oats and wheat. The distributions of M. dirhodum and Sitobium spp. along sheltered perimeters of all crops were apparently similar.     

The rhizosphere microflora of wheat grown under controlled conditions I. The effect of soil fertility and urea leaf treatment on the rhizoplane microflora

Summary Microbial colonization of seminal roots of seedlings and of nodal roots of tillering plants was studied on spring wheat ‘Kaspar’ cultivated in growth, chambers. Methods were developed to microbially condition the soil before seeding and to regulate soil humidity. Addition of inorganic nutrients (NPK) to the soil increased the number of rhizoplane bacteria and actinomycetes, but did not effect the number of fungi on seminal and nodal roots. Urea leaf treatments stimulated bacteria and actinomycetes 7 and 9 days after treatment. Fourteen days after urea leaf treatment, however, bacterial numbers were mostly reduced, especially on seminal roots, while numbers of actinomycetes generally equalled the control. Root types and soil fertility did not obviously interact with the effect of urea leaf treatment on rhizoplane bacteria and actinomycetes. The only effect of urea on total numbers of fungi, was a reduction of their numbers on seminal roots 9 days after treatment at both NPK-levels.     

Lacewings (Chrysopidae,Neuroptera) in cereal agrocenoses of the forest-steppe of Western Siberia

Twelve species of lacewings: Chrysopa altaica, Ch. commata, Ch. perplexa, Ch. phyllochroma, Ch. dasyptera, Ch. carnea, Ch. formosa, Ch. intima, Ch. perla, Ch. prasina, Ch. septempunctata, and Nineta inpunctata were found in cereal agroecosystems of the forest-steppe zone of Western Siberia. The dominant species were Ch. carnea and Ch. phyllochroma. The biological characteristics, seasonal dynamics of the abundance of lacewings in the agrocenoses of winter rye, spring wheat, and oats are given. The abundance of larval and adult lacewings in the spring wheat agrocenosis was not affected by the level of chemicalization (upon condition of the rational use of insecticides), tillage variant, and predecessor crop. In the years when the density of lacewings was low, no differences in their population were found between the agrocenoses of wheat (after fallow), winter rye, oats, vetch-oats, canola, barley, and barley with melilot. In the years characterized by relatively high abundance of lacewings, they occurred more frequently in the crop rotations with wheat after fallow and with oats. These plants were settled by cereal aphids to the greatest extent. In all the years studied, the density of lacewings on alfalfa was 2–2.8 times as great as that on wheat after fallow.     

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.     

Growth and development of root systems of winter cereals grown after different tillage methods including direct drilling

Summary A method is described for rapidly estimating the depth of penetration and density of roots of cereal crops under field conditions. Counts of living roots, traversing horizontal faces of soil cores, were made for winter wheat growing on direct-drilled and ploughed land.The rate of penetration of roots of winter wheat in a clay and a sandy loam soil averaged 5 mm per day throughout winters without extremes of cold or wet. Death of roots near the soil surface occurred wilst others continued downward penetration. The rate of root elongation was slower during prolonged periods when the soil was wet and faster,i.e. to greater depths, during dry conditions.Damage sustained to roots during adverse winter conditions ofter varied between direct drilling and ploughing. More roots at depth were consistently recorded on direct-drilled than on ploughed land when measured in spring after a soil water deficit had developed during the preceding month. After prolonged wet soil conditions during the winter on a soil with a large clay fraction and low hydraulic conductivity, root growth and penetration in spring, before the development of a soil water deficit, was more restricted on direct-drilled than on ploughed land.     

Invasion and development of the cereal cyst-nematode Heterodera avenae in roots of barley infected by the take-all fungus Gaeumannomyces graminis

Observations on the invasion and development of Heterodera avenae in relation to take-all infection of barley roots were made in three pot experiments. Post-cropping H. avenae populations were lower on fungus-infected plants, as a result of the production of fewer, smaller and less fecund cysts. The reduction in cyst numbers was associated with reduced larval invasion of take-all infected roots and with the effects of the unfavourable environment of these roots on female development, possibly through its effects on sex determination and survival of the larvae.     

Nucleotide sequence and molecular analysis of the low temperature induced cereal gene, BLT4

Summary The nucleotide sequence and derived amino acid sequence of a cDNA clone (BLT4) for a low temperature induced barley gene were determined. This gene, together with a small family of related genes, was shown to reside on chromosome 3. The BLT4 clone has homology with genes in wheat and oats. Its expression was studied in oats and in barley doubled haploid lines segregating for spring/winter habit and for frost hardiness. These analyses show that elevated steady state levels of BLT4 mRNA are produced in shoot meristematic tissue after 3 days low positive temperature treatment. The low temperature response was found in all barley doubled haploid lines and was therefore not associated specifically with either the spring/winter habit or frost hardiness. Elevated levels of BLT4 mRNA were also seen in drought-stressed barley and it is likely that this is a gene encoding a low molecular weight protein that is responsive to dehydrative stresses, such as cold and drought.The EMBL accession number for BLT4 is X56547 H. vulgare cDNA     

Death of the cereal root cortex: its relevance to biological control of take-all

Cell death in the root cortex of cereals was assessed by an inability to detect nuclei, using acridine orangelfluorescence microscopy after fixation and mild acid hydrolysis. Seminal roots were scanned at x 100 magnification and their cortices were considered dead when nuclei were absent from all cell layers except the innermost one, adjacent to the endodermis; this cell layer remains alive long after the rest of the cortex has died. Cortical death of wheat and barley roots occurred in the absence of major pathogens. Cell death started behind the root hair zone of the main root axis, initially in the outermost cell layer of the cortex and then progressively inwards towards the endodermis; however, the cortex remained alive for a distance of c. 800 μm around emerging root laterals. The rate of cortical death was more rapid in wheat than in barley, both under field conditions and in the glasshouse at 20 °C. Thus, field-grown spring wheat (Sicca) showed 50% death of the root cortex in the top 6 cm of first seminal roots after 35 days (growth stage 1–2), whereas spring barley (Julia) showed 50% death of the root cortex after 67 days (growth stage 8). In the glasshouse, the top 9 cm of first seminal roots on 16-day plants showed 55% cortical death in wheat (Cappelle-Desprez) but only 2.5% cortical death in barley (Igri). The same rates of death were found in all subsequent seminal roots. The wheat root cortex died at the same rate in sterile and unsterile conditions, and at the same rate in the presence/absence of Phialophora radicicola Cain var. graminicola Deacon or Aureobasidium bolleyi (Sprague) von Arx. Hence, although P. radicicola and other soil microorganisms may benefit from root cortex death they do not exert biological control of take-all by enhancing or retarding the rate of this process. To study the effects of cortical death on take-all, Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker was point-inoculated at the tips and on older (5 and 15 day) regions of wheat seminal roots. After 17 days at 20 °C the fungus had grown to the same extent as runner-hyphae in all cases, but the severity of disease decreased with increasing age of the root cortex prior to inoculation; thus, G. graminis caused most extensive vascular discoloration and most intense vascular blockage in roots inoculated at their tips. Similar experiments on wheat and barley roots inoculated separately with P. radicicola and G. graminis suggest that at least three factors associated with cortical death influence infection by these fungi: (1) initially, cell death may enhance infection because nutrients are made available to the parasites and host resistance within the cortex is reduced; (2) weak parasites and soil saprophytes may colonise dead and dying cortices in competition with G. graminis and P. radicicola and thereby reduce infection by these fungi; (3) changes in the endodermis and adjacent cell layers may be associated with cortical death and may retard invasion of the stele. Future work will seek to establish the relative importance of these factors and extend this study to other cereal host-fungus combinations.