Stem Base Diseases Research Articles

Development of stem-base pathogens on different cultivars of winter wheat determined by quantitative PCR

The progress of development of stem-base pathogens in crops of second winter wheat was plotted in nine experiments in three years. The amount of each pathogen present was determined by quantitative PCR. Where Tapesia yallundae was present in quantifiable amounts, it usually developed earlier than the other eyespot pathogen, T. acuformis. Both species were usually present in greater amounts on cultivars which are more susceptible to eyespot. The sharp eyespot pathogen, Rhizoctonia cerealis, developed more erratically than either of the Tapesia spp. and there were no consistent effects on different cultivars. Fusarium spp., the cause of brown foot rot, were rarely present in quantifiable amounts, but Microdochium nivale was usually present as one or both of the varieties nivale and majus. Late-season (after anthesis) decreases in M. nivale suggest that any brown foot rot symptoms attributable to this fungus would have fully developed earlier. Cultivar differences in amounts of M. nivale were most clear in stems during internode extension and when relatively large amounts of DNA were present. Such differences approximately reflected eyespot susceptibility, cv. Soissons containing most and cv. Lynx containing least DNA. The results emphasise the difficulty in relating diagnoses, by quantitative PCR or other means, at early growth stages when decisions to apply fungicides against stem-base disease are made, to later disease severity.

Factors affecting diseases of winter wheat in England and Wales, 1989–98

The above article was published without a number of the author's corrections included. The publisher offers their unreserved apology for this and the sections affected are reprinted below in their entirety.Samples from 360 to 450 randomly selected winter wheat crops in England and Wales were collected annually during the milky ripe development stages (GS 73–75) from 1989 to 1998. The number of samples from each region was proportional to the area of winter wheat grown. The percentage area affected by disease was assessed on the top two leaves and the ear, and the incidence and severity of stem base diseases were also recorded. An estimate of the percentage area of the crop affected by Barley yellow dwarf virus (BYDV) and take‐all (Gaeumannomyces graminis) was made in the field. Septoria leaf blotch (Septoria tritici, teleomorph Mycosphaerella graminicola) was the major foliar disease recorded, with an average maximum severity of 7·8% of the area of leaf 2 affected in 1998. Eyespot (Tapesia spp.) was the major stem base disease, with the highest incidence of stems falling into the damaging moderate plus severe categories (18·9%) in 1998. Levels of powdery mildew (Blumeria graminis) showed a decline from 0·4% of the area of leaf 2 in 1989 to 0·1% in 1998. This fall was associated with a reduction in the proportion of disease‐susceptible cultivars grown. There were significant regional differences in levels of septoria leaf blotch, brown rust (Puccinia recondita), eyespot, sharp eyespot (Rhizoctonia cerealis) and BYDV. The percentage of crops treated with a fungicide rose from 96% in 1989 to 98% in 1998 and the mean number of spray applications per crop rose during this period from 2·1 to 2·5. A higher proportion of crops was treated with fungicides between the end of tillering and fifth node detectable (GS 29–35) than around flag leaf emergence (GS 36–48) or ear emergence (GS 49–71). Prior to 1994, the majority of late fungicide sprays was applied at, or after, ear emergence, but from 1994, the majority was applied around flag leaf emergence. The value and socioeconomic implications of the results are discussed.

Factors affecting diseases of winter wheat in England and Wales, 1989–98

Samples from 360 to 450 randomly selected winter wheat crops in England and Wales were collected annually during the milky ripe development stages (GS 73–75) from 1989 to 1998. The number of samples from each region was proportional to the area of winter wheat grown. The percentage area affected by disease was assessed on the top two leaves and the ear, and the incidence and severity of stem base diseases were also recorded. An estimate of the percentage area of the crop affected by barley yellow dwarf virus (BYDV) and take‐all (Gaeumannomyces graminis) was made in the field. Septoria leaf blotch (Septoria tritici, teleomorph Mycosphaerella graminicola) was the major foliar disease recorded, with an average maximum severity of 7·8% of the area of leaf 2 affected in 1998. Eyespot (Tapesia spp.) was the major stem base disease, with the highest incidence of stems falling into the damaging moderate plus severe categories (18·9%) in 1998. Levels of powdery mildew (Blumeria graminis) showed a decline from 0·4% of the area of leaf 2 in 1989 to 0·1% in 1998. This fall was associated with a reduction in the proportion of disease‐susceptible cultivars grown. There were significant regional differences in levels of septoria leaf blotch, brown rust (Puccinia recondita), eyespot, sharp eyespot (Rhizoctonia cerealis) and BYDV. The percentage of crops treated with a fungicide rose from 96% in 1989 to 98% in 1998 and the mean number of spray applications per crop rose during this period from 2·1 to 2·5. A higher proportion of crops was treated with fungicides between the end of tillering and fifth node detectable (GS 24–35) than around flag leaf emergence (GS 36–48) or ear emergence (GS 49–71). Prior to 1994, the majority of late fungicide sprays was applied at, or after, ear emergence, but from 1994, the majority was applied around flag leaf emergence. The value and socioeconomic implications of the results are discussed.

Biology and control of stem-base diseases of cereals in the UK

Biology and control of stem-base diseases of cereals in the UK

Effects of cultivar and fungicides on stem‐base pathogens, determined by quantitative PCR, and on diseases and yield of wheat

SummaryThe polymerase chain reaction (PCR) was used to identify and quantify all fungal pathogens of wheat (Triticum aestivum) stem bases in nine field experiments at three locations in England. The main aim was to apply quantitative PCR to provide robust data on the efficacy of new fungicides against the individual components of the stem‐base disease complex. Cyprodinil most effectively controlled eyespot by decreasing both pathogens, Tapesia yallundae and T. acuformis (the most widespread species), and sometimes contributed to increased yields. Prochloraz controlled eyespot less consistently, its effectiveness dependent mainly on the presence of T. yallundae or on rainfall events soon after application. Azoxystrobin contributed to yield increases most consistently. Although it decreased sharp eyespot and its pathogen, Rhizoctonia cerealis, these effects were insufficient to account for much of the yield increases. The effects of fungicides on eyespot were sometimes greatest on the most susceptible cultivars. Amounts of Tapesia DNA were usually consistent with cultivar susceptibility ratings. The only pathogens of brown foot rot present in significant amounts were Microdochium nivale vars nivale and majus. They appeared not to affect yield or to respond greatly to fungicides. The susceptibility of cultivars to these pathogens was sometimes similar to their susceptibility to eyespot, suggesting that they may respond to the same host resistance genes or may in some cases be secondary colonisers of eyespot‐infected plants.

Chromosomal location of Fusarium head blight resistance genes and analysis of the relationship between resistance to head blight and brown foot rot

AbstractIn order to identify chromosomes involved in resistance to Fusarium head blight, a set of 21 substitution lines of Triticum macha (resistant) chromosomes into ‘Hobbit’'sib’(susceptible) were evaluated in trials over 2 years. For the first year's trial, all plants were inoculated on the same day with a conidial suspension of F. culmorum. For the second trial, individual plants were inoculated precisely at mid anthesis of each plant over a period of 2 weeks. The disease level was assessed by visual scoring, relative ear weight and F. culmorumn‐specfic quantitative polymerase chain reaction. The results showed that T. macha chromosomes 1B, 4A and 7A conferred good overall resistance, suggesting that they carry important genes for resistance. In two additional trials, T. macha and ‘Hobbit’'sib’ were evaluated for resistance to brown foot rot. The results showed that T. macha was more susceptible than ‘Hobbit’‘sib’, indicating that stem base disease response is not correlated with head blight resistance in these cultivars.

Distinguishing isolates of cereal stem disease pathogens of the genus Tapesia from isolates of Fusarium and Rhizoctonia using the RAPD method

The RAPD method (Random Amplification of Polymorphous DNA) was used to distinguish Tapesia acufonnis and T. yallundae isolates from other pathogens of wheat stem base diseases (Fusarium avenaceum, F. culmorum, F. nivale, Rhizoctonia cerealis and R. so/ani).Isolates of the fungi originated from infected wheat plants (Triticum aestivum L.) collected at various locations in the Czech Republic. Three decameric oligonucleotide-primers were selected as producing genotype-specific RAPD products. These markers distinguish all isolates of the above taxons. The intra-species genetic variability of these species also was studied. The values of Dice's coefficients of similarity suggest that isolates of Tapesia yallundae showed a higher degree of intra-species variability than those ofT acufonnis. A high degree of intra-species variability was identified also in Fusarium avenaceum.

Visual disease and PCR assessment of stem base diseases in winter wheat

Stem base disease (eyespot, sharp eyespot and brown foot rot) was assessed visually and by the polymerase chain reaction (PCR) technique on single plants sampled at four‐week intervals in two crops of winter wheat grown in the UK in 1992–3. PCR assays were conducted for Fusarium avenaceum, F. culmorum, both varieties of Microdochium nivale, both eyespot‐causing species of Tapesia and Rhizoctonia cerealis. PCR diagnoses were compared with visual diagnoses at each time point. Eyespot was caused principally by T. acuformis (R‐type) and developed rapidly late in the season. Visual diagnoses of eyespot were largely confirmed by PCR but T. acuformis was detected in many plants lacking eyespot symptoms. R. cerealis was detected at relatively low incidences on both sites, and sharp eyespot visual diagnoses did not correlate with the incidence of any of the pathogens assayed by PCR. Brown foot rot, caused principally by Microdochium nivale var. majus, accumulated earlier in the season than eyespot. Overall, visual diagnoses of stem base disease coincided poorly with PCR data until after growth stage (GS) 30.

Detection and quantification ofFusarium culmorumandFusarium graminearumin cereals using PCR assays

Random amplified polymorphic DNA assays were used to identify amplification products characteristic of eitherFusarium culmorumorFusarium graminearum. Selected fragments were cloned, sequenced and primer pairs were developed which permitted specific detection ofF. culmorumorF. graminearumusing conventional PCR. Quantitative assays were developed for bothF. culmorumandF. graminearum, using competitive PCR. TheF. culmorum-specific competitive PCR assay was used to study the effect of inoculum load and timing on stem base disease of winter wheat caused byF. culmorum. The extent of fungal colonization, as measured by fungal DNA content, was greater on plants inoculated earlier in the season and increased with increasing conidial load. TheF. graminearum-specific competitive PCR assay was used to study the colonization of wheat grain by trichothecene producing and non-producing isolates ofF. graminearum. Colonization of grain by trichothecene producing isolates was greater than that by non-producing isolates, supporting the view that trichothecenes act as virulence factors in the colonization of wheat byF. graminearum. The results from competitive PCR assays were compared with those for visual disease assessment in both instances.

A comparison of management regimes for one-year rotational set-aside within a sequence of winter wheat crops, and of growing wheat without interruption. 3. Effects on diseases

Different management regimes for 1-year rotational set-aside were tested in three experiments that followed winter wheat and started in autumn 1988–90. The regimes included operations that prevented the establishment of volunteers or allowed them to establish and persist until either spring or summer, and also altered the distribution of debris from the winter wheat that preceded the set-aside. For comparison, treatments in the set-aside year also included winter wheat.Samples taken in spring from the first test crop showed that there were few significant or consistent effects on leaf diseases of growing the wheat after different set-aside treatments or after winter wheat. There were significant effects of the set-aside treatments on root and stem base diseases but some of the effects, and the apparent absence of others, are not easily reconciled with current understanding of the biology of the pathogens concerned. In summer, eyespot (Pseudocercosporella herpotrichoides) was most severe after winter wheat and least severe after ryegrass. Severity after the other set-aside treatments did not differ significantly. There was more sharp eyespot (Rhizoctonia cerealis) in plots that had been ploughed at the start of the set-aside year, including those sown with winter wheat, than in those that had not. Brown foot rot (Fusarium spp.) was equally severe where the wheat followed wheat or where it followed set-aside treatments that allowed volunteers to develop, and less so where the development of volunteers was prevented. Take-all (Gaeumannomyces graminis var. tritici) was most severe after winter wheat and more severe after set-aside treatments that allowed volunteers to develop and survive through the winter than after those that did not. Effects of ryegrass (Lolium perenne ssp. multiflorum) on take-all in the following wheat were particularly variable, perhaps because ryegrass is a host of both the take-all fungus and of Phialophora graminicola, one of its principal antagonists.

Stem-base disease and fungal colonisation of winter wheat grown in compost inoculated with Fusarium culmorum, F. graminearum and Microdochium nivale

Fungal colonisation of winter wheat cv. Cadenza by Fusarium culmorum, F. graminearum and Microdochium nivale was studied under conditions designed to avoid the splash dispersal of conidia from infested compost, to evaluate the possibility that systemic growth may transfer infection from the stem-base to the head. At decimal growth stages 33, 59, 77–87 and 95 the extent of fungal growth was assessed using a sample of 72 plants, by the recovery of fungal species from the stem-base, from each node and from the ear. Each of the fungi was recovered from stem tissues above soil level in some, apparently symptomless, plants. Symptoms of Fusarium foot rot were seen in an increasing proportion of plants during grain-fill and desiccation. There was an inverse relationship between recovery and the height above stem-base from which the stem tissue was excised. F. culmorum was the most frequently isolated fungus and it was also recovered from the highest position in plants. Only 3% of plants were colonised above the second node and none of the fungal species were recovered from either the fifth node or the ear. This suggests that colonisation and systemic growth from Fusarium infested compost is unlikely to contribute to the development of ear blight symptoms in winter wheat.

Differentiation and quantification of the cereal eyespot fungi Tapesia yallundae and Tapesia acuformis using a PCR assay

Isolates of Tapesia yallundae and Tapesia acuformis were subjected to Random Amplified Polymorphic DNA (RAPD) assay. Amplification products common to isolates of either species were cloned and primers were generated from each sequence for use in conventional PCR. The primer pair derived from a T. yallundae specific RAPD marker amplified a product only from DNA of T. yallundae isolates and not from DNA of a range of other fungal species associated with the stem base disease complex of cereals. Similarly, the primer pair generated from a T. acuformis‐specific RAPD marker amplifed a product only from DNA of T. acuformis isolates. Quantitative assays were developed for both species of Tapesia from these primer pairs, using competitive PCR. Competitive PCR was used to determine the level of colonization of seedlings by each species in glasshouse‐ and field‐inoculated cereal hosts and results compared to those for conventional seedling disease assessment.

Surveys of stem base diseases and fusarium ear diseases in winter wheat in England, Wales and Scotland, 1989–1990

SummaryAn investigation into the incidence of stem base diseases and the pathogens associated with them was undertaken on winter wheat samples collected at growth stages 31 and 73–75 in 1989 and 1990. Symptoms at growth stage 31 were classified into 10 different types based on visual characteristics. Although Pseudocercosporella herpotrichoides was associated mainly with eyespot lesions and Rhizoctonia spp. with sharp eyespot lesions, a significant number of isolates of each pathogen were taken from lesions classified as fusarium. Different types of fusarium lesion on stem bases at both growth stages were not associated with any one particular Fusarium or Microdochium species. 98% of P. herpotrichoides isolates obtained from eyespot lesions at growth stage 31 in 1989, and 87% of those obtained in 1990 were identified as the sub‐species P. herpotrichoides var. acuformis, Microdochium nivale was more common than any of the Fusarium species at both growth stages, and was particularly prevalent in samples from Scotland at the earlier growth stage in 1989. Isolations from the top internodes at growth stage 73–75 indicated that systemic infection by Fusarium species, although present in some stems, was of little importance. Fusarium ear blight affected 0.4% of ears in 1989 and 0.5% in 1990. Glume spot lesions on the ears in 1990 were predominantly associated with Fusarium poae.

Surveys of diseases of winter barley in England and Wales, 1981–1991

SummarySamples from 200–400 randomly selected winter barley crops were taken annually at growth stage 71–73 from 1981 to 1991, with the exception of 1984 and 1985. The number of samples from each region was proportional to the area of barley growth in each region. The percentage of the area of the top two leaves affected by diseases and the severity of stem base diseases were recorded. Mildew (Erysiphe graminis) was the most widespread of the foliar diseases and in three years (1982, 1986 and 1991) was also the most severe. Rhynchosporium (Rhynchosporium secalis), net blotch (Pyrenophora teres) and brown rust (Puc‐cinia hordei) were also prevalent in some years. Of the stem base diseases, fusarium was often the most widespread. Eyespot (Pseudocercosporella her‐potrichoides) severity varied widely from year to year ranging from 1.2% of stems affected by moderate or severe symptoms in 1982 to 24.1% in 1988. There were regional differences in the severity of mildew, rhynchosporium, brown rust, halo spot (Selenophoma donacis) and eyespot. Cultivar resistance affected disease severity and previous cropping affected eyespot and less frequently mildew, rhynchosporium and net blotch. Eyespot, and to a lesser extent, sharp eyespot, were less severe in late‐ than in early‐sown crops. The percentage of crops treated with a fungicidal spray increased from 72% in 1981 to 95% in 1991. The use of benzimidazole fungicides for the control of eyespot declined in response to the development of resistance, and more recently the use of prochlo‐raz also declined. Broad spectrum DMI fungicides were widely used, and the use of morpholines to improve mildew control increased significantly. The proportion of crops grown from seed treated with a non‐mercurial fungicidal seed dressing reached a peak of 47% in 1986 but subsequently declined to 22% in 1990 and 1991.

Crop rotation with pure stands and mixtures of barley and wheat to control stem and root rot diseases

Crop rotations are known to be a natural barrier against a wide range of fungal soil-borne pathogens. Results shown in this paper are based on observations that were made in the third growing period of a 3-year cereal crop rotation (1989–1991). Mixtures as pre-crops and main crops were compared with pure stands of barley and wheat also grown as pre- and main crops. After this 3-year period, field experiments showed that interspecific mixtures of winter barley and winter wheat reduced stem rot caused by Pseudocercosporella herpotrichoides, Fusarium spp., Gaeumannomyces graminis and Rhizoctonia cerealis. Growing barley and wheat after a cereal mixture resulted in an increased number of healthy plant stems. The pre-crop mixture significantly reduced the disease incidence of Fusarium spp. on barley (> 50%) during stem elongation and ripening. Disease incidence of G. graminis on barley during ripening decreased from 44% after barley to 9% when grown after the mixture. Differences in take-all incidence on wheat due to different pre-crops were not significant. The percentage of P. herpotrichoides lesions on wheat grown in a mixture increased after pre-crops containing barley. Furthermore, interactions occurred between pathogens, indicating differences in competition. Additional effects on plant health were observed where barley-wheat mixtures were grown for 2 years. In general, the incidence of stem base diseases was lowest in mixtures that were grown after a mixture. Disease reductions on wheat grown in a mixture after a mixed pre-crop were comparable to those disease reductions brought about by chemical fungicides applied in pure stands of wheat. Pathogen frequency on wheat hypocotyl and root tissue was estimated using a selective medium: the frequency of G. graminis on wheat tissue decreased from 14% after the pre-crop barley and 7% after the pre-crop wheat, to 1% after the pre-crop mixture. The frequency of Fusarium spp. was generally not affected, but the spectrum of species changed quantitatively. A greater number of weak or non-pathogenic fungi were isolated from wheat segments when the plants were grown after a mixed pre-crop.

Disease-induced losses in winter wheat in England and Wales 1985–1989

Annual surveys of winter wheat diseases in England and Wales provide information on the relative severity of the leaf and stem-base disease complex. Septoria tritici was the most damaging disease during the 5-year period 1985–1989 causing annual losses estimated to be 0.329 Mt compared with 0.251 Mt and 0.231 Mt for eyespot and mildew, the next most damaging winter wheat diseases. Annual losses during the period averaged 1.078 Mt excluding losses attributable to the fusarium diseases, for which no satisfactory yield loss relationships are available. Sowing date and length of break from cereals exert a strong influence on incidence of eyespot and losses attributable to the disease and, on the basis of these surveys, growing all winter wheat crops after a 1-year break would prevent national losses of ∼ 100 kt annually.

Surveys of diseases of winter wheat in England and Wales, 1976–1988

SummarySamples from 300 – 400 randomly selected winter wheat crops were taken annually at growth stage 73 – 75 from 1976 to 1988 with the exception of 1983 and 1984. The number of samples from each region was proportional to the area of wheat grown in each region. The percentage of the area of the top two leaves affected by diseases, the severity of ear and stem base diseases and, in 6 years, the severity of take‐all were recorded. Septoria tritici and Septoria nodorum were, on average, the most severe of the foliar diseases and eyespot (Pseudocercosporella herpotrichoides) was the most severe of the stem base diseases. Regional differences in levels of S. tritici, brown rust, sharp eyespot and nodal fusarium were significant. Cultivar resistance affected disease severity, and previous cropping patterns particularly affected take‐all and eyespot. Eyespot and sharp eyespot were less severe in late‐ than in early‐sown crops. The percentage of crops treated with a fungicidal spray increased from 14% in 1976 to over 90% between 1983 and 1985. Use of benzimidazole fungicides applied at growth stage 31 declined, while use of morpholines from flag leaf emergence onwards increased between 1985 and 1988.

Surveys of cereal diseases and pests in the Netherlands. 2. Stem-base diseases of winter wheat

In the period 1974–1986, ca. 100 commercial winter wheat fields were surveyed annually for stembase diseases. In these years, on average 6% of the tillers was infected with eyespot in spring at the first-second, node stage. Eyespot intensity in spring was high in years with high temperature during winter. Eyespot, intensity in the milky-ripe stage in July, averaged 13% of the culms and was high in years with high temperature in April and high precipitation in March, April and May. These data may improve forecasts.

Assessment of eyespot and other stem base diseases of winter wheat and winter barley

A dichotomous key is presented which describes the symptoms of eyespot, sharp eyespot and brown foot rot (Fusarium spp.) on winter cereals at the seedling through to adult plant growth stages. Sampling and disease assessment methods for these diseases are also described.

Surveys of Diseases of Winter Wheat in England and Wales, 1970–75

SUMMARYSamples from 265–333 randomly selected crops of winter wheat in England and Wales were taken annually from 1970 to 1975 after heading, the main sample being at the milky‐ripe growth stage. The percentage of the area of the top two leaves affected by diseases was recorded and, in the last five years, samples were tested for infection by barley yellow dwarf virus: in 1975 stem base diseases were recorded. Scptoria was the most common and severe disease in four of the six years. In. 1970 mildew was most severe and, in 1975, brown rust. The severity of infection by Septoria tended to be greater in southern and western areas in wetter summers and in crops following a previous cereal. Yellow rust was most severe in 1972, when it was very prevalent on cv. Joss Cambier. In 1973 the disease was less severe, but in 1974 and 1975 the severities of both yellow and brown rusts increased in association with the popularity of susceptible cultivars. There was a tendency for yellow rust to be more severe on early‐sown crops. In 1975, eyespot was recorded on 11·8 per cent of the stems. 1·8 per cent of the symptoms being severe. Fungicidal sprays were associated with a slightly smaller incidence of stem base diseases. Estimates of percentage loss in yield due to particular diseases vary from almost zero caused by yellow rust in 1970 to 7·4 per cent loss caused by Septoria in 1972.