Subcrown Internodes Research Articles

A review on common root rot of wheat and barley in Australia

AbstractCommon root rot (CRR) caused by the soilborne pathogen Bipolaris sorokiniana (teleomorph Cochliobolus sativus) is becoming increasingly prevalent worldwide. Identification of CRR is difficult and time‐consuming for human assessors due to the non‐distinctive above‐ground symptoms, with browning of subcrown internodes and roots the most distinguishing symptom of infection. CRR disease has been recognized as a significant disease for cereal crops in many countries. In 2009, CRR in Australia was estimated to cause $30 million average annual yield loss for wheat and $13 million for barley. Recent evidence indicates CRR may be more prevalent than expected in Australian wheat cropping areas due to lack of research on this disease. Low levels of B. sorokiniana survive in the soil for up to 10 years and attack plants at early stages of growth. Therefore, mitigating CRR in wheat and barley may not be practical at the late stages of infection due to lack of effective methods; however, early detection might be viable to alleviate the impact of this disease. A comprehensive overview of CRR caused by B. sorokiniana, including disease background, worldwide economic losses, management methods, potential CRR detection using multispectral and hyperspectral sensors and the research focus over the past 50 years is provided in this article. This review paper is expected to provide thorough supplemental information for current studies about CRR and proposes recommendations for whole‐of‐field disease scouting methods to farmers, enabling reduced time and cost for CRR management and increasing wheat and barley production worldwide.

Identification of Fungal Species Associated with Crown and Root Rots of Wheat and Evaluation of Plant Reactions to the Pathogens in North Dakota

Common root rot (CRR) and crown rot (CR), caused by Bipolaris sorokiniana and Fusarium species, respectively, can cause significant yield losses in cereal crops. To assess the prevalence, incidence, and severity of these diseases in North Dakota, wheat samples were collected from spring wheat fields across the state in 2012, 2013, and 2014. Based on sub-crown internode symptoms, a greater incidence and severity of CRR was observed in 2012 (warm and dry year) than in 2013 and 2014. Also, the Northwestern Glaciated Plains and Northwestern Great Plains ecoregions showed greater CRR incidence and severity compared to the Northern Glaciated Plains and Lake Agassiz Plains ecoregions in the state. Bipolaris sorokiniana and Fusarium species including F. acuminatum, F. avenaceum, F. culmorum, F. graminearum, F. equiseti, F. pseudograminearum, F. oxysporum, F. redolens, F. sporotrichioides, and F. solani were isolated and identified from the root and crown tissues of the wheat samples. B. sorokiniana was isolated more frequently than other fungal species in all sampled years and ecoregions of North Dakota. F. acuminatum, F. avenaceum, F. culmorum, F. equiseti, F. graminearum, F. pseudograminearum, and F. redolens were pathogenic causing infections on seedlings of the two wheat genotypes (ND652 and Alsen), whereas isolates of F. oxysporum and F. solani were non-pathogenic and considered as secondary invaders associated with the root and crown rot diseases. Evaluation of some spring wheat genotypes for reactions to one B. sorokiniana isolate at seedling and adult plant stages, and one F. culmorum isolate at the seedling stage indicated that susceptibility to these pathogens varied among different wheat genotypes tested. This study provides useful information on fungal species associated with root and crown rots of wheat in North Dakota and on resistant/susceptible reactions of some spring wheat lines to the different fungal isolates evaluated.

Cluster Analysis Of Triticum L. Samples Of Different Ecological And Geographical Origin

This research paper is devoted to the application of cluster analysis for evaluating samples of soft spring wheat by elements of crop structure. The purpose of the study is to analyse the intraspecific and interspecific variability of morphological features of samples of spring wheat of various ecological and geographical origin according to 8 morphological features. Observations were carried out in 2018-2020 in the training and experimental production centre “Doslidne pole” of the Kharkiv National Agrarian University named after V.V. Dokuchaev. The cluster analysis of the collection of spring wheat samples, which included 76 samples of various ecological and geographical origin, allowed the study to assess the following features: the presence of awns, the colour of awns, the colour of ear scales, the pubescence of leaves, the pubescence of the subcrown internode, the pubescence of the ear internode, the colour of caryopsis, the colour of straw. The results of analysis of the phylogeny of various types of spring wheat by cluster analysis using morphological markers to determine homogeneous groups are presented, and the affected tree of systematic formation of clustering groups is established. Based on the cluster analysis, two separate groups of soft spring wheat samples were identified according to the complex of plant productivity elements. Samples are grouped into each cluster depending on the quantitative characteristics of the crop structure and their interaction with each other. In general, all samples over the years of study showed good results, namely based on “colour of awns”, of particular note are the samples of the Tr. persicumspecies. According to the results obtained, all samples have good indicators, and cluster analysis of soft spring wheat samples allowed identifying groups of plants that exceed the parent forms in the optimal set of economically valuable traits, which would allow for a more purposeful selection of valuable forms based on certain traits

Comparison of disease severity caused by four soil-borne pathogens in winter cereal seedlings

In Australia, crown rot of cereals is predominantly caused by Fusarium pseudograminearum and Fusarium culmorum, and common root rot by Bipolaris sorokiniana. Fusarium graminearum is an important pathogen causing Fusarium head blight worldwide and has also been reported to cause crown rot of wheat. The comparative ability of F. pseudograminearum, F. culmorum, F. graminearum and B. sorokiniana to cause crown rot and common root rot across a range of winter cereal species requires investigation. In glasshouse trials, we inoculated one cultivar each of barley, bread wheat, durum wheat, oat and triticale with two strains of each of the four pathogens. At 21 days after inoculation, the sub-crown internode and leaf sheaths of each plant were visually rated for brown discoloration. Shoot length and dry weight of inoculated plants were compared with those of non-inoculated controls. Barley and bread wheat had the highest disease severity ratings on leaf sheaths and sub-crown internode (64.7–99.6%), whereas oat had the lowest disease severity ratings across all pathogens (<5%). The shoot length of all cultivars was significantly reduced (by 12.2–55%, P < 0.05) when exposed to F. pseudograminearum. This study provides a comparison of pathogenicity of crown rot and common root rot pathogens and demonstrates significant variation in visual discoloration and host response across a range of winter cereals.

Seedling elongation responses to gibberellin seed treatments in wheat

AbstractThe wheat (Triticum aestivum L.) Reduced height (Rht) alleles are widely used to prevent lodging through semi‐dwarfism. Seedling elongation and coleoptile length can be significantly decreased by some of these alleles, leading to reduced soil emergence after deep sowing in certain semi‐arid environments. Application of the elongation‐promoting hormone gibberellin A3 (GA3) as a seed treatment has been used as an alternative to improve seedling emergence. Seedling responses to GA3 seed treatment were investigated under controlled conditions in a collection of varieties differing for Rht dwarfing alleles and the ability to emerge from deep planting. Data between treated and untreated seed were collected on overall coleoptile length and emergence from deep planting in simulated pot studies. Gibberellin‐sensitive varieties, carrying either no dwarfing gene or the Rht8 dwarfing gene, responded to the GA3 seed treatment with increased coleoptile and subcrown internode elongation. Comparison of near‐isogenic lines carrying no dwarfing allele or the GA‐insensitive Rht‐B1b and/or Rht‐D1b semi‐dwarfing alleles showed that GA insensitivity was associated with reduced seedling response to GA3 seed treatment. However, there was variation in seedling elongation and GA3 response in a collection of GA‐insensitive varieties. Thus, it cannot be assumed that all Rht‐B1b and Rht‐D1b varieties will fail to respond to GA3 seed treatment. Interestingly, some better emerging GA‐insensitive varieties had longer coleoptiles after treatment, suggesting that selection for better emergence in semi‐arid regions of the U.S. Pacific Northwest may have led to responses in GA3 application independent of the dwarfing gene used.

Fusarium Crown Rot Whitehead Symptom as Influenced by Wheat Crop Management and Sampling Date.

Symptoms of Fusarium crown rot of wheat include premature death of inflorescens (whiteheads), lesions on subcrown internodes, and rotting of crown tissue and lower stem internodes. Each symptom type is influenced by a different set of environmental conditions. Whiteheads are the easiest symptom to quantify and are frequently reported in the Pacific Northwest U.S.A. The objective of this research was to examine factors associated with whitehead expression and relationships with wheat yield and test weight. Incidence of whiteheads differed for inoculations with different isolates of F. pseudograminearum and F. culmorum, and over years due to weather factors. Whiteheads became less as planting dates for winter wheat were delayed until after September, and incidence was increased with increasing nitrogen application rate. Dates of initial and greatest expression of whiteheads differed among cultivars, which was associated in part with the cultivar heading date. Whiteheads were not correlated with subcrown internode lesions or browning of crown tissue. Whiteheads were also not correlated with grain test weight. Whiteheads were sometimes negatively associated with grain yield, but that relationship was variable and could not be considered a reliable, recurrent, or accurate measure of crown rot severity. These results indicate the need for caution in reporting whiteheads as a sole indicator of cultivar susceptibility to Fusarium crown rot.

Fusarium crown rot caused by Fusarium pseudograminearum in cereal crops: recent progress and future prospects.

Diseases caused by Fusarium pathogens inflict major yield and quality losses on many economically important plant species worldwide, including cereals. Fusarium crown rot (FCR), caused by Fusarium pseudograminearum, is a cereal disease that occurs in many arid and semi-arid cropping regions of the world. In recent years, this disease has become more prevalent, in part as a result of the adoption of moisture-preserving cultural practices, such as minimum tillage and stubble retention. In this pathogen profile, we present a brief overview of recent research efforts that have not only advanced our understanding of the interactions between F.pseudograminearum and cereal hosts, but have also provided new disease management options. For instance, significant progress has been made in the genetic characterization of pathogen populations, the development of new tools for disease prediction, and the identification and pyramiding of loci that confer quantitative resistance to FCR in wheat and barley. In addition, transcriptome analyses have revealed new insights into the processes involved in host defence. Significant progress has also been made in understanding the mechanistic details of the F.pseudograminearum infection process. The sequencing and comparative analyses of the F.pseudograminearum genome have revealed novel virulence factors, possibly acquired through horizontal gene transfer. In addition, a conserved pathogen gene cluster involved in the degradation of wheat defence compounds has been identified, and a role for the trichothecene toxin deoxynivalenol (DON) in pathogen virulence has been reported. Overall, a better understanding of cereal host-F.pseudograminearum interactions will lead to the development of new control options for this increasingly important disease problem. Taxonomy: Fusarium pseudograminearum O'Donnell & Aoki; Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium. Disease symptoms: Fusarium crown rot caused by F.pseudograminearum is also known as crown rot, foot rot and root rot. Infected seedlings can die before or after emergence. If infected seedlings survive, typical disease symptoms are browning of the coleoptile, subcrown internode, lower leaf sheaths and adjacent stems and nodal tissues; this browning can become evident within a few weeks after planting or throughout plant development. Infected plants may develop white heads with no or shrivelled grains. Disease symptoms are exacerbated under water limitation. Identification and detection: Fusarium pseudograminearum macroconidia usually contain three to five septa (22-60.5× 2.5-5.5μm). On potato dextrose agar (PDA), aerial mycelia appear floccose and reddish white, with red or reddish-brown reverse pigmentation. Diagnostic polymerase chain reaction (PCR) tests based on the amplification of the gene encoding translation elongation factor-1a (TEF-1a) have been developed for molecular identification. Host range: All major winter cereals can be colonized by F.pseudograminearum. However, the main impact of this pathogen is on bread (Triticum aestivum L.) and durum (Triticum turgidum L. spp. durum (Dest.)) wheat and barley (Hordeum vulgare L.). Oats (Avena sativa L.) can be infected, but show little or no disease symptoms. In addition, the pathogen has been isolated from various other grass genera, such as Phalaris, Agropyron and Bromus, which may occur as common weeds. Useful websites: https://nt.ars-grin.gov/fungaldatabases/; http://plantpath.psu.edu/facilities/fusarium-research-center; https://nt.ars-grin.gov/fungaldatabases/; http://www.speciesfungorum.org/Names/Names.asp.

English

Successful stand establishment is prerequisite for optimum crop yields and can be affected by seeding depth. A field experiment was conducted to investigate the effects of seeding depth on agronomical characteristics, structural feature of subcrown internode (SCI), plant growth and ultimately grain yield of winter wheat. Seeds of Luyuan 502 were sown at four seeding depths (10, 25, 40 and 55 mm). The results showed that increasing the seeding depth from 10 to 40 mm increased seedling emergence rate, numbers of fall tillers per unit area and per plant. Seeding at 55-mm depth significantly decreased the seedling emergence, tillering capacity, spikes per unit m 2 ; however, the fertile tiller percentage significantly increased compared with shallower seeding. At 10-mm soil depth, there was no SCI produced; at 25 to 55-mm soil depth, the length of SCI increased with increasing of depth. However, the diameter of SCI and diameter and wall thickness of SCI xylem vessel decreased. Regarding hormonal concentration in SCI, GA3 and IAA increased with increasing seeding depth, whereas the maximum ZR and ABA contents were observed at 40-mm soil depth. Similarly, the maximum rate of oxygen consumption was also observed in SCI of 40-mm-sown plants. Transmission electron microscope observations showed many mitochondria in the companion cell (CC) and many plasmodesma connecting CC and sieve element. As the seeding depth increased, values of the normalized difference vegetative index and shoot dry matter weight decreased but interestingly, the highest grain yield was obtained in 40-mm-sown wheat, followed immediately by that at 55-mm depth. It is concluded that wheat sown at about 40-mm soil depth may be optimal for winter wheat growth and production in northern China.

Effect of wheat cultivars, fertilizers, and fungicides on Fusarium foot rot disease of wheat

Fusarium culmorum is a principal causal agent of root, crown, and foot rot disease in the wheat-growing areas of Turkey. The effects of different fertilization practices, fungicide sprays, and cultivar reactions of 12 wheat varieties were investigated for disease development in greenhouse conditions in 2006-2007. The fertilizers used in the experiments significantly reduced disease by 27.5%-54.7% compared to the nonfertilized control. The plants fertilized with calcium ammonium nitrate (26% N) or composite NPK (15%, 15%, 15%) showed fewer disease symptoms than those fertilized with NPK (20%, 20%, 0%) in the presowing applications. On the other hand, foot rot severity was lower with ammonium nitrate (33% N) than urea (46% N) when applied as a supplement in the 25th and 45th growth stages of the Zadoks scale. Furthermore, fungicide sprays and seed dressing treatments also decreased foot rot symptoms. Seed treatment with tebuconazole lowered disease severity in the subcrown internode compared to the control and it was overall the most effective fungicide with 47.8% efficacy. When plants were sprayed with fluquinconazole, tebuconazole, or epoxyconazole + carbendazim (two times at Zadoks growth stages 31 and 45), disease severity decreased by 96.3%, 93.9%, and 91.0%, respectively. In the cultivar reaction tests, no stable or considerable tolerance was observed in the 12 wheat varieties against foot rot. It may be concluded from this study that fertilizer forms and fungicide preference can play an important role where Fusarium foot rot is the main problem in wheat-growing areas.

A simple approach to assess common root rot severity incidence data in wheat

Common root rot (CRR) of wheat, caused by Cochliobolus sativus, produces discoloration of the subcrown internodes (SCIs) and is directly related to yield losses. It is critical to clearly define and standardize the CRR assessment methods to avoid subjectivity and variability between assessors. Therefore, in this study, a comparison between the incidence (I; proportion of diseased SCIs) and the severity (S; proportion of SCI showing CRR symptoms) was investigated to explore the possibility of simplifying disease rating. Assessments were made visually at multiple sample sites in artificially- and naturally-inoculated research and production fields for three growing seasons. Significant differences (P = 0.001) in mean I and S values were found among cultivars, with values being consistently higher in the susceptible ones. However, CRR severity increased linearly as incidence increased in both Triticum durum and T. aestivum wheat. Their slopes and intercepts of the I–S relationship were consistent over the three growing seasons. This result may be considered a significant contribution for CRR assessment in wheat breeding programs.

Root rot severity and fungal populations in spring common, durum and spelt wheat, and Kamut grown under organic management in western Canada

Fernandez, M. R., Fox, S. L., Hucl, P., Singh, A. K. and Stevenson, F. C. 2014. Root rot severity and fungal populations in spring common, durum and spelt wheat, and Kamut grown under organic management in western Canada. Can. J. Plant Sci. 94: 937–946. A 3-yr field study (2010 to 2012) was conducted in the Brown soil zone of southwest Saskatchewan to determine the reactions of common, durum and spelt wheat cultivars currently registered in western Canada, and of Kamut wheat, to common root rot (CRR) under organic management. The genotypes selected for this study are often grown by organic producers in this region. Over the 3 yr of this study, Cochliobolus sativus, the main causal agent of CRR, was the fungus most frequently isolated from discoloured subcrown internodes, followed by Fusarium spp. The latter constituted an overall total of over 19% of all isolations and consisted of at least 12 different species, the most frequently detected of which were F. equiseti, F. avenaceum, F. acuminatum and F. oxysporum. The relative prevalence of the most commonly isolated genera/species agrees most closely with previous studies conducted under organic management. In general, C. sativus was less common in Kamut than in durum and spelt wheat, and it was more frequently isolated from durum than common wheat. In contrast, there were few differences in the isolation of Fusarium spp. among wheat species. Their isolation was greater for common wheat and Kamut than for durum wheat. For all 3 yr, the greatest mean CRR severity was observed in spelt wheat, followed by durum wheat and Kamut, with common wheat having the lowest average severity. For individual cultivars, the durum wheat AC Avonlea, Kyle and Transcend had the greatest CRR severity of all cultivars in this species and CDC Verona the lowest. Common wheat cultivars AC Elsa, CDC Kernen and Red Fife had the greatest CRR severity and Superb and Unity the lowest severity within their species. Under organic conditions, avoiding growing cultivars with high susceptibility to CRR is recommended given the expected presence of this disease in most fields and environments.

A simple method for assessing severity of common root rot on barley.

Common root rot caused by Cochliobolus sativus is a serious disease of barley. A simple and reliable method for assessing this disease would enhance our capacity in identifying resistance sources and developing resistant barley cultivars. In searching for such a method, a conidial suspension of C. sativus was dropped onto sterilized elongated subcrown internodes and incubated in sandwich filter paper using polyethylene transparent envelopes. Initial disease symptoms were easily detected after 48h of inoculation. Highly significant correlation coefficients were found in each experiment (A, B and C) between sandwich filter paper and seedling assays, indicating that this testing procedure was reliable. The method presented facilitates a rapid pre-selection under uniform conditions which is of importance from a breeder’s point of view.

Current Status of Cereal Root Diseases in Western Australia Under Intensive Cereal Production and Their Comparison with the Historical Survey Conducted During 1976–1982

AbstractTwo separate surveys of root diseases of cereals in the Western Australian (WA) cereal belt were conducted: the first conducted annually for wheat and barley during 1976–1982 and the second for wheat during 2005–2007. For the 1976–1982 survey, the cereal belt was divided into 15 zones based on the location and rainfall. Sampling was representative of the actual cropping area, with both wheat and barley sampling sites selected by zone as a percentage of total sites. Over 31 000 plants were assessed from a total of 996 fields. Average take‐all incidence ranged from 3% in the northern low rainfall zone to 57% in the southern high rainfall zone. Other root diseases assessed included rhizoctonia root rot, fusarium crown rot and subcrown internode discolouration. During the 2005–2007 survey, around 20 000 plants from a total of 210 fields being intensively cropped with cereals were surveyed for take‐all, rhizoctonia root rot, fusarium crown rot, common root rot, root lesion nematode and cereal cyst nematode. The 2005–2007 survey results indicated that root and crown diseases prevailed in paddocks frequently cropped with cereals and occurred at damaging levels across all WA cropping districts surveyed. The more recent root disease survey identified that the fungal diseases rhizoctonia root rot and fusarium crown rot and the root lesion nematode were the most serious impediments to intensive cereal production, particularly in the southern region of WA. Comparing the 2005–2007 results with the previous survey of 1976–1982, the relative importance of take‐all appears to have declined over the past 30 years.

Spread of Fusarium pseudograminearum in wheat seedling tissues from a single inoculation point

Inoculation of wheat seedlings by the crown rot pathogen Fusarium pseudograminearum is commonly used to screen for resistance based on leaf sheath discolouration. While leaf sheath discolouration is effective for describing disease reactions, the degree to which the pathogen colonises the full range of seedling host tissues is an important aspect of the disease process, which has not been systematically examined. After single point droplet inoculation of the coleoptile, quantitative PCR was used to determine the spread of F. pseudograminearum into different host tissues during crown rot pathogenesis at 14 and 28 days after inoculation. Quantitative PCR and visual assessment indicated that while most seedling tissues (leaf sheath, leaf blade, sub-crown internode, primary root and secondary root) were colonised, the basal portion of leaf sheath tissue supported the highest density of F.pseudograminearum. Other significant sites of colonisation were the upper leaf sheath and sub-crown internode. By comparison, the quantity of mycelium detected in the primary and secondary roots was significantly lower, while the infection of leaf blade tissues was severely restricted.

Fusarium culmorum: causal agent of foot and root rot and head blight on wheat

Fusarium culmorum is a ubiquitous soil-borne fungus able to cause foot and root rot and Fusarium head blight on different small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in contamination of the grain with mycotoxins. This review summarizes recent research activities related to F. culmorum, including studies into its population diversity, mycotoxin biosynthesis, mechanisms of pathogenesis and resistance, the development of diagnostic tools and preliminary genome sequence surveys. We also propose potential research areas that may expand our basic understanding of the wheat-F. culmorum interaction and assist in the management of the disease caused by this pathogen. Fusarium culmorum (W.G. Smith) Sacc. Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium. Foot and root rot (also known as Fusarium crown rot): seedling blight with death of the plant before or after emergence; brown discoloration on roots and coleoptiles of the infected seedlings; brown discoloration on subcrown internodes and on the first two/three internodes of the main stem; tiller abortion; formation of whiteheads with shrivelled white grains; Fusarium head blight: prematurely bleached spikelets or blighting of the entire head, which remains empty or contains shrunken dark kernels. IDENTIFICATION AND DETECTION: Morphological identification is based on the shape of the macroconidia formed on sporodochia on carnation leaf agar. The conidiophores are branched monophialides, short and wide. The macroconidia are relatively short and stout with an apical cell blunt or slightly papillate; the basal cell is foot-shaped or just notched. Macroconidia are thick-walled and curved, usually 3-5 septate, and mostly measuring 30-50 × 5.0-7.5 μm. Microconidia are absent. Oval to globose chlamydospores are formed, intercalary in the hyphae, solitary, in chains or in clumps; they are also formed from macroconidia. The colony grows very rapidly (1.6-2.2 cm/day) on potato dextrose agar (PDA) at the optimum temperature of 25 °C. The mycelium on PDA is floccose, whitish, light yellow or red. The pigment on the reverse plate on PDA varies from greyish-rose, carmine red or burgundy. A wide array of polymerase chain reaction (PCR) and real-time PCR tools, as well as complementary methods, which are summarised in the first two tables, have been developed for the detection and/or quantification of F. culmorum in culture and in naturally infected plant tissue. Fusarium culmorum has a wide range of host plants, mainly cereals, such as wheat, barley, oats, rye, corn, sorghum and various grasses. In addition, it has been isolated from sugar beet, flax, carnation, bean, pea, asparagus, red clover, hop, leeks, Norway spruce, strawberry and potato tuber. Fusarium culmorum has also been associated with dermatitis on marram grass planters in the Netherlands, although its role as a causal agent of skin lesions appears questionable. It is also isolated as a symbiont able to confer resistance to abiotic stress, and has been proposed as a potential biocontrol agent to control the aquatic weed Hydrilla spp. http://isolate.fusariumdb.org/; http://sppadbase.ipp.cnr.it/; http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://plantpath.psu.edu/facilities/fusarium-research-center; http://www.phi-base.org/; http://www.uniprot.org/; http://www.cabi.org/; http://www.indexfungorum.org/

Symptom development proceeds at different rates in susceptible and partially resistant cereal seedlings infected with Fusarium pseudograminearum

Variation in the reaction of cereal cultivars to crown rot caused by Fusarium spp., in particular Fusarium pseudograminearum, was identified over 50 yrs ago, however the parameters and pathways of infection by F. pseudograminearum remain poorly understood. Seedlings of wheat, barley and oat genotypes that differ in susceptibility to crown rot were inoculated with a mixture of F. pseudograminearum isolates. Seedlings were harvested from 7 to 42 days after inoculation and expanded plant parts were rated for severity of visible disease symptoms. Individual leaf sheaths were placed onto nutrient media and fungal colonies emerging from the leaf sheathes were counted to estimate the degree of fungal spread within the host tissue. Significant differences in both the timing and the severity of disease symptoms were observed in the leaf sheath tissues of different host genotypes. Across all genotypes and plant parts examined, the development of visible symptoms closely correlated with the spread of the fungus into that tissue. The degree of infection of the coleoptile and sub-crown internode varied between genotypes, but was unrelated to the putative resistance of the host. In contrast leaf sheath tissues of the susceptible barley cv. Tallon and bread wheat cv. Puseas scored higher disease ratings and consistently showed faster, earlier spread of the fungus into younger tissues than infections of the oat cv. Cleanleaf or the wheat lines 2–49 and CPI 133814. While initial infections usually spread upwards from near the base of the first leaf sheath, the pathogen did not appear to invade younger leaf sheaths only from the base, but rather spread laterally across from older leaf sheaths into younger, subtended leaf sheaths, particularly as disease progressed. Early in the infection of each leaf sheath, disease symptoms in the partially resistant genotypes were less severe than in susceptible genotypes, however as infected leaf sheaths aged, differences between genotypes lessened as disease symptoms approached maximum values. Hence, while visual scoring of disease symptoms on leaf sheaths is a reliable comparative measure of the degree of fungal infection, differences between genotypes in the development of disease symptoms are more reliably assessed using the most recently expanded leaf sheaths.

Crop Management Effects on Root and Crown Rot of Wheat in West‐Central Saskatchewan, Canada

The impact of cropping system management on root and crown rot of spring wheat (Triticum aestivum L.) was examined on a Dark Brown Chernozem (Typic Boroll) soil in the Canadian Prairies. This systems approach tried to reflect the most common practices of organic and conventional producers in this region. The study consisted of a factorial combination of three input levels (high, with tillage, fertilizer and pesticides; reduced [RED], with conservation tillage, targeted fertilizer and weed control; and organic [ORG] with tillage and N‐fixing legumes); and three levels of cropping diversity (low diversity with wheat and summerfallow or legume green manure fallow; diversified using annual grain crops; and diversified using annual grain crops and perennial forages). All rotations were 6 yr long. Subcrown internodes and crowns/lower culms of wheat plants were scored for discoloration, and fungi in discolored tissue were identified and quantified. Overall, input level had a greater impact on disease levels and fungal frequency than cropping diversity. Discoloration severity was lowest in the RED systems, which was attributed to lower percentage isolation of Cochliobolus sativus, the most common pathogen. Fusarium species varied with input level. The pathogens F. avenaceum and F. culmorum were most associated with RED and/or least associated with ORG systems, whereas the weak pathogen/saprophyte F. equiseti was most associated with ORG systems. Thus, ORG management helped to reduce populations of F. avenaceum and F. culmorum, two of the most important Fusarium pathogens in the Canadian Prairies.

Effect of fungicide seed treatments on root pathogens of cereal crops under field conditions

It is of importance to reduce the spread of Fusarium graminearum to western regions of the Canadian prairies where Fusarium head blight has so far occurred to a limited extent. Determining the effectiveness of fungicides against F. graminearum in infected seed under various growing conditions will help design a comprehensive strategy for preventing the spread of this pathogen. Field trials at various locations in eastern Saskatchewan were conducted (2003-2005) to examine the performance of registered and experimental fungicides on Fusarium colonization of subcrown internodes (SIs) of plants derived from Fusarium-infected barley (Hordeum vulgare L.), common (Triticum aestivum L.) and durum [T. turgidum L. ssp. durum (Desf.) Husn.] wheat seed, and on SI discoloration. Among the fungi isolated from discolored SIs were Fusarium spp., including F. graminearum, and Cochliobolus sativus. Fusarium graminearum infections were mostly seed-borne whereas infection by other fungi appeared to be mostly soil-borne. Compared with the untreated infected control, the combined seed treatments reduced discoloration of SIs, but no single fungicide reduced discoloration consistently across site-years or crops. Similarly, no product consistently reduced the isolation of F. graminearum or other Fusarium pathogens, although some fungicides appeared to be more effective than others in reducing isolation of F. graminearum or C. sativus. Our observations agree with results from a controlled-environment study of effects of seed treatments on F. graminearum colonization of plants derived from infected common and durum wheat seed, thus confirming that treatment of F. graminearum-infected seed with fungicides will not likely prevent the spread of this pathogen.

Spread of seed-borne Erwinia rhapontici in bean, pea and wheat

Studies were conducted in the laboratory and greenhouse to determine the distribution of Erwinia rhapontici in plants arising from naturally infected seeds of pea or artificially inoculated seeds of bean and wheat, and whether the pathogen is transmitted to the subsequent generation of seeds. Infected seeds were planted in pots of Cornell mix in the greenhouse, and sampled at specified intervals throughout the plant growth cycle (seedling stage, elongation stage, flowering stage, seed formation stage, and maturity). Plating of surface sterilized lateral roots, tap roots, basal stems, mid-stems, apical stems, petioles, pods, and seeds of pea and bean, and of lateral roots, sub-crown internodes, basal stems, mid-stems, apical stems, peduncles, glumes, and seeds of wheat revealed that the bacterial pathogen spread from infected seeds to the lower parts of the plant tissues, but failed to spread further to the seeds produced on these plants. The study concludes that E. rhapontici did not establish systemic infection throughout the plants. Possible mechanisms of infection of seeds are discussed.

Glyphosate associations with cereal diseases caused by Fusarium spp. in the Canadian Prairies

Fusarium pathogens cause important diseases, such as root/crown rot and Fusarium head blight (FHB), in cereal crops. These diseases can be caused by similar Fusarium spp. Common root rot (CRR) is widespread in the western Canadian Prairies, whereas FHB has potential of becoming an important disease in this region. There are no commercially available cereal cultivars with good resistance to these diseases. It is therefore important to identify agronomic practices that could affect levels of Fusarium pathogens in cereals. This review deals primarily with the effects of tillage systems and glyphosate use on the development of FHB and CRR in wheat and barley in eastern Saskatchewan. Although the FHB study in 1999–2002 indicated that environment was the most important factor determining FHB development, previous glyphosate use and tillage practice were among the production factors with the greatest association with FHB. Overall, disease was highest in crops under minimum-till management. Previous glyphosate use was consistently associated with higher FHB levels caused by the most important FHB pathogens, Fusarium avenaceum and Fusarium graminearum. Cochliobolus sativus, the most common CRR pathogen, was negatively associated with previous glyphosate use, while F. avenaceum, F. graminearum, and other fungi were positively associated, suggesting that glyphosate might cause changes in fungal communities. The occurrence and isolation of F. avenaceum from cereal residues were greater under reduced-till than conventional-till while C. sativus was most common under conventional-till, and F. graminearum was lowest under zero-till. Previous glyphosate applications were again correlated positively with F. avenaceum and negatively with C. sativus. These observations agreed with results from the FHB and CRR studies. These are the first studies that established a relationship between previous glyphosate use and increased Fusarium infection of spikes and subcrown internodes of wheat and barley, or Fusarium colonization of crop residues. However, because of the close association between noncereal crops, reduced tillage and glyphosate use, it was not possible to completely separate the effects of these factors on Fusarium infections. Determining the relative contribution of these popular production trends to the development of diseases caused by Fusarium spp. are essential for devising appropriate agronomic recommendations to prevent their further spread in western Canada, and to reduce the impact that these diseases are having in areas where they are already established. The consistent association between previous glyphosate use and Fusarium infections also warrants further research to elucidate the nature of this association and the underlying mechanisms determining these effects.