T. K. Turkington

Reaction of seedling roots of 14 crop species to Fusarium graminearum from wheat heads

To increase our understanding of the epidemiology of fusarium head blight of wheat and barley, a study was conducted under controlled conditions to determine whether Fusarium graminearum Schwabe from wheat can cause seedling blight or root rot in various crop species. Inoculum of F. graminearum, consisting of a wheat floret infected with the pathogen, was placed adjacent to surface-sterilized seed of each crop in a sterile potting mix. Wheat, barley, oat, rye, triticale, canaryseed, flax, canola (Brassica napus L. and Brassica rapa L.), mustard, bean, field pea, lentil, and chickpea were included in the study. Seedling emergence and root rot severity were scored at 3–4 weeks after seeding. The effect of temperature on seedling blight severity was also tested in barley cv. Brier. Inoculation reduced emergence in all crops, except canola, mustard, and field pea, and increased root rot severity in most crops. Emergence of seedlings was not affected at the lowest temperature (10:5°C day:night) and no root infection occurred. However, as the temperature increased from 10 to 30°C, seedling emergence and establishment were reduced and root rot severity increased. Infection of roots, crowns, and seedlings of the crops grown in rotation with wheat indicates that these crops may act as alternative hosts to F. graminearum.

Soil microbial biomass and diversity after herbicide application

Greenhouse and field experiments were conducted to investigate the effects of herbicides on soil microbial C (microbial biomass), bacterial diversity and community structure. In the first greenhouse experiment, 12 herbicides were applied at recommended rates to a Gray Luvisolic soil contained in trays. Soil samples were collected 0, 1, 2, 3 and 4 wk after treatment and analysed for microbial C and bacterial diversity. The second greenhouse experiment was similar to the first, but only 6 of the 12 herbicides were applied to a Gray Luvisolic and Black Chernozemic soil. The same six herbicides were applied to the Gray Luvisolic soil at a field site near Fort Vermilion, Alberta, and to the Black Chernozemic soil at Lacombe, Alberta, in 2000. In the first greenhouse experiment, metribuzin, imazamox/imazethapyr, triasulfuron and metsulfuron methyl reduced microbial C compared with glufosinate ammonium and sethoxydim. In the second greenhouse experiment, microbial diversity as determined by Shannon index was low...

Relative aggressiveness and production of 3- or 15-acetyl deoxynivalenol and deoxynivalenol by Fusarium graminearum in spring wheat

Abstract Fusarium graminearum is the principal cause of fusarium head blight in North America, a disease that has caused severe losses in yield and quality of cereals. In North America, the vast majority of F. graminearum isolates produce 3- or 15-acetyl deoxynivalenol (ADON) in addition to DON. Until recently, 15-ADON isolates predominated, but a rapid shift from 15-ADON to 3-ADON producers in Canada and north central USA has been documented. In order to better understand the effect of this population shift on relative aggressiveness of isolates and mycotoxin accumulation, we tested a total of 58 isolates for 3- and 15-ADON production on two Canadian spring wheat cultivars, ‘Roblin’ (susceptible) and ‘5602 HR’ (moderately resistant). In Experiment 1, three isolates from the Canadian provinces of Manitoba, Saskatchewan and Alberta, each of which produced either 15-ADON or 3-ADON, were tested using spray inoculation. In Experiment 2, 20 isolates which produced 15-ADON and 20 which produced 3-ADON from Manitoba, were tested using point inoculation. There were no significant differences in aggressiveness among isolates based either on geographic origin or mycotoxin type. Analysis of seeds from inoculated heads by gas chromatography/mass spectrometry indicated that the 3-ADON producing isolates had significantly higher DON levels than the 15-ADON isolates in ‘Roblin’ after both spray and point inoculation and in ‘5602HR’ after point inoculation. DON levels following point inoculation by 15-ADON isolates were similar in the two cultivars. The 15-ADON isolates from Alberta produced less DON than 15-ADON isolates from Manitoba and Saskatchewan. Consistently, more ADON was produced by 15-ADON isolates than by 3-ADON isolates. The results of the study suggest that if the percentage of 3-ADON isolates in Canada increases, DON levels in cereals are likely to increase in epidemic years.

A PCR-Based Assay to Detect Rhynchosporium secalis in Barley Seed

A polymerase chain reaction (PCR)-based diagnostic assay was developed to detect Rhynchosporium secalis, the barley scald fungus, in barley seed. Species-specific primers were designed based on sequence data of a region consisting of the 5.8S RNA gene and internal transcribed spacers 1 and 2 of R. secalis. The sequenced regions showed 100% homology between the two R. secalis isolates and 93% homology between R. secalis and R. orthosporum. Five sets of synthesized oligonucleotide primers were tested for their specificity using 29 isolates of R. secalis of diverse geographic origins and from different barley cultivars. In addition, DNA extracts from 22 species of microbes either taxonomically related to or from the same niche as R. secalis were tested as negative controls. Among five sets of primers, a primer set, RS8 and RS9, was selected for use in detecting R. secalis because it amplified a 264-bp fragment from the DNA of all R. secalis isolates but not the DNA from other species used for validation of the specificity of this primer set. This primer set was also used to detect R. secalis in barley seed and successfully amplified the predicted size of the DNA fragment in the infected material. PCR detection of as little as 1 to 10 pg of R. secalis DNA was possible. The method described here requires 1 day for completion, compared to 10 days required for the cultural method.

Fungal plant pathogens infecting barley and wheat seed from Alberta, 1995-1997

From 1995 to 1997, spikes were collected from a total of 160 barley and 188 wheat fields from the Peace River region to the Three Hills area of Alberta, Canada. After threshing, 100 seeds from each field were surface sterilized, incubated on potato dextrose agar, and examined for the presence of the following pathogens: Fusarium graminearum, other Fusarium spp., Cochliobolus sativus, Pyrenophora tritici-repentis, Pyrenophora graminea, Pyrenophora teres, and Stagonospora nodorum. Fusarium graminearum was not detected in any seed samples. The most common Fusarium species isolated was Fusarium avenaceum. Maximum seed infection levels with F. avenaceum in a single field were 51 and 37% for barley and wheat, respectively. Substantial levels of seed-borne P. teres were found in barley with maximum infection levels of 82, 81, and 89% in 1995, 1996, and 1997, respectively. Stagonospora nodorum was also commonly found in both barley and wheat seed with maximum infection levels of 61 and 54%, respectively. Pyrenophora tritici-repentis, P. graminea, and C. sativus were generally present at low levels.

Effect of dry heat treatment on seed-borne Fusarium graminearum and other cereal pathogens

Pathogen levels and seed viability of two samples each of barley (Hordeum vulgare) (B1, B2), Canada western red spring wheat (Triticum aestivum) (RS1, RS2), and Canada western amber durum wheat (AD1, AD2) were assessed after heating seed at 50 or 70°C for up to 14 days. RS2 and B2, with an initial incidence of 23 and 84% of Fusarium graminearum, respectively, were also heated at 60°C for 24 days and 80°C for 10 days. Pathogen levels and seed viability were assessed by plating seed onto potato dextrose agar and wet filter paper, respectively. Fusarium graminearum was eliminated from RS2 after 15 days at 60°C, 5 days at 70°C, or 2 days at 80°C. In B2, F. graminearum was eliminated after 21 days at 60°C, 9 days at 70°C, or 5 days at 80°C. After heating at 50 or 70°C, the observed frequency of Cochliobolus sativus in B1 declined slightly but significantly over time, whereas it substantially increased in B2. A significant decline in the incidence of C. sativus was observed in B2 after heating at 80°C. Pyrenophora teres was observed significantly more often in B1 after heating at 50 or 70°C, whereas Pyrenophora tritici-repentis in AD1 and AD2 was unaffected by heating at 50°C. However, the detection of P. tritici-repentis did significantly increase over time in AD2 when heated at 70°C. In AD1, heating at 70°C initially increased, then decreased the observed incidence of this pathogen. Cochliobolus sativus, P. teres and P. tritici-repentis were still viable in the samples after 14 days of heating at 70°C, but C. sativus was not detected after 10 days at 80°C. Germination of wheat tempered to 12, 14, and 16% moisture content was unaffected by heating at 70°C for 7 days, whereas barley tempered to the same moisture content had a slight decline in germination. Germination rates in most samples were unaffected by the treatment times and temperatures sufficient to eradicate F. graminearum, but a significant decline in viability was recorded for AD2 and B1 heated at 70°C. The germination of B2 increased when heated at 70°C, but declined when heated at 80°C. It is recommended that thermotherapy be applied to control national and international movements of F. graminearum and other heat-sensitive pathogens in germplasm used for research and breeding purposes.Key words: thermotherapy, Cochliobolus sativus, Pyrenophora teres, Pyrenophora tritici-repentis.

Pathogenic variation of Rhynchosporium secalis in Alberta

Leaf samples with scald symptoms were taken from various barley cultivars in 1997 and 1998 at nine locations in Alberta for examination of pathogenic variability. Two hundred and fifty-six single-spore isolates of Rhynchosporium secalis were differentiated into 52 pathotypes using 12 differentials, which consisted of seven accessions with major resistance genes and five commercial cultivars. Fifty-two percent of isolates were virulent on cv. Harrington only (pathotype 1); five pathotypes, consisting of close to 25% of isolates, were virulent only on 4 of 5 commercial cultivars; and about 45 pathotypes, consisting of about 25% of isolates, were virulent on commercial cultivars and accessions. No differential was resistant to all pathotypes, and many pathotypes were represented by single isolates. There was a difference in pathotype diversity and complexity among locations in Alberta. Calmar, Lacombe, and Edmonton sites comprised the greatest number of pathotypes that were virulent on up to seven differentials; at the Beaverlodge, Carstairs, Stettler, and Westlock sites, pathotype 1 comprised more than 60% of total isolates with a few other pathotypes. The Trochu and Vegreville sites were intermediate in the number of pathotypes. Discriminant analysis based on the reactions of the 12 differentials also showed divergence in R. secalis virulence among locations. Pathogenic variability associated with location in Alberta is important in the context of breeding for resistance and use of the most resistant cultivars by producers.

Residue decomposition and blackleg of canola: influence of tillage practices

The influence of tillage regime on the decomposition of shoot and root residues of canola (Brassica napus, Brassica rapa) infested with the virulent strain of Leptosphaeria maculans and disease levels was evaluated from 1993 to 1997, near Beaverlodge, Alberta. Fall mold-board ploughing in October 1993 was most effective at reducing the amount of canola residue, especially for the first 2 years. Residue retention was also greater for zero tillage than for conventional tillage. After 3 years, residue amounts were low for all tillage treatments. Initially shoot residues were more abundant than root residues, but the rate of decomposition for shoot residues was higher than for root residues. Soil disturbance as a result of tillage and seeding operations appeared to bring some residue, especially root residues, to the soil surface, resulting in a nonlinear relationship between residue weight and time. Low levels of blackleg were found in the canola grown in 1997 and were not significantly different among tillage treatments. A rotation including barley, field peas, and wheat for 3 years following canola helped to eliminate potential disease sources under all tillage systems used in this study.

Virulence of Puccinia striiformis on wheat and barley in central Alberta

Abstract Sixty-one field collections of Puccinia striiformis, primarily from central Alberta during 2007–2008, were identified to be P. striiformis f. sp. tritici (Pst) or P. striiformis f. sp. hordei (Psh) based on virulence on differential seedlings. Wheat differentials separated 38 Pst isolates into 13 pathotypes, with most pathotypes consisting of single isolates. Two pathotypes consisted of two isolates, and three pathotypes were represented by three, seven and 16 isolates. Wheat lines with resistance genes Yr1, Yr5, Yr15 and YrSP were resistant to all 13 pathotypes, while wheat lines with genes Yr10, Yr24 and Yr28 were resistant to 82–92% of the isolates. Differentials YrA, Yr2, Yr6, Yr7, Yr8, Yr9, Yr17, Yr26, Yr27, Yr31 and YrCV were susceptible to 71–100% of the isolates. Twenty-three Psh isolates were identified to 15 Psh pathotypes, with virulence on two to eight barley differentials, including ‘Topper’, ‘Hiproly’, ‘Varunda’, ‘Abed Binder 12’, ‘Trumpf’, ‘Mazurka’, ‘Bigo’, ‘I 5’ and ‘Bancroft’ and avirulent on ‘Heils Franken’, ‘Emir’ and ‘Astrix’. Ten pathotypes consisted of a single isolate, four pathotypes had two isolates and one pathotype consisted of five isolates. The possible origin and virulence of P. striiformis pathotypes in central Alberta is discussed in relation to using cultivar resistance for disease control.

The impact of soil incorporation of canola residues and stubble application of chemicals on decomposition and inoculum production by Leptosphaeria maculans.

The impact of incorporating residues into soil and applying chemicals to stubble was evaluated on canola residue decomposition and inoculum production by Leptosphaeria maculans during August and November 1994 and April and September 1995. Residue decomposition, measured as the loss in residue dry weights, was more rapid in the incorporated residues than in the surface-placed residues up to the first sampling date but was similar in both treatments from the second to the last sampling dates. Averaged over all treatments, soil incorporation of residues resulted in a 40% weight reduction during the study compared with 27% for surface-placed residues. Following incubation of residues on vermiculite at 16°C for 4 weeks, higher pycnidiospore levels of L. maculans were observed in the incorporated versus the surface-placed residues. Without the 4-week incubation, pycnidiospore production on the sampled residue was lower for incorporated residues for the first three sampling dates but not for the final sampling date. Treating blackleg-infected canola stem bases with liquid N (28-0-0) + glucose, urea (46-0-0), RoundUp® (glyphosate), Stubble Digest-All® powder, or a distilled water control had no effect on canola decomposition and sporulation by L. maculans.