K. Xi

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.

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.

Impact of seedbed utilization and fungicide application on severity of net blotch [Pyrenophora teres] and production of barley

Limited information is available regarding the impact of seed placement and row spacing, and their interaction with fungicides, on leaf diseases and agronomic performance of barley. A direct-seeding field experiment was conducted at three locations in Canada (Lacombe and Beaverlodge (Alberta) and Melfort (Saskatchewan)), in 1999–2000, to evaluate the effect of three seedbed utilization treatments and six foliar fungicide timing and rate treatments on disease severity and production characteristics of barley. Seedbed treatments included row spacing at 23 or 30 cm with a knife opener, or spread bands with a 28-cm sweep and a 23-cm row spacing. Fungicide treatments included full and split applications of propiconazole at Zadoks growth stages (GS) 12, 37, and 58 with an untreated control. Severity of net blotch [Pyrenophora teres] was higher for the 23- and 30-cm distinct row spacings compared with the spread-band placement using sweeps. The interaction between seed placement and fungicide application was not significant for net-blotch severity, indicating that disease response to fungicide did not vary with seed-placement configuration. Overall, grain yield was affected by seed placement, with the spread band having slightly higher yield, especially when compared with the 30-cm distinct row spacing, but the response to seed placement did vary over year × location combinations, and with fungicide treatment. Kernel weight, plumpness, and test weight were greatest for the spread-band placement, although this response varied among year × location combinations. Fungicide applications at late growth stages (GS 37 and GS 58) reduced net-blotch severity and increased grain yield and kernel quality, whereas applications at GS 12 generally had a limited impact. Planting in distinct rows may have resulted in higher disease severity and lower kernel weight, plumpness, and test weight by facilitating spore dispersal and subsequent net-blotch development compared with the spread-band placement.

Impact of crop management on leaf diseases in Alberta barley fields, 1995-1997

Conservation tillage may increase the risk of leaf diseases for Alberta barley producers. A study was undertaken from 1995 to 1997 to assess the impact of the tillage system, crop rotation, and cultivar resistance on levels of scald [Rhynchosporium secalis] and net blotch [Pyrenophora teres] in commercial barley (Hordeum vulgare) fields. Scald and net-blotch levels were assessed in 99, 148, and 91 barley fields in 1995, 1996, and 1997, respectively, throughout Alberta. Fields were classified according to tillage regime (conventional, zero, and minimum tillage), cultivar resistance to both diseases, and crop rotation. The tillage system did not influence the probability of higher levels of scald or net blotch in all 3 years. The previous crop did influence the probability of higher levels of scald in 1995 and 1996; fields previously planted to barley were 3–4 times more likely to have greater scald severity than fields planted to a nonhost crop. The previous crop affected the level of net blotch in 1995 only; fields previously planted to barley were 4.5 times more likely to have increased disease severity compared with fields previously planted to a nonhost. Cultivar resistance to either scald or net blotch was the management factor that most consistently reduced the probability of a higher level of disease. On average, susceptible cultivars were 4–8 and 5–12 times more likely to have higher levels of scald and net blotch, respectively, compared with resistant cultivars.

The influence of Roundup® on in vitro growth and sporulation of Rhynchosporium secalis and Pyrenophora teres

The objective of this study was to investigate the in vitro influence of glyphosate (Roundup®) on growth and sporulation of Pyrenophora teres and Rhynchosporium secalis in agar petri plate cultures. Agar media amended with glyphosate concentrations of 0, 0.025, 0.050, 0.075, 0.100, 0.125, 0.250, and 0.500 µL/mL were inoculated with a spore suspension of R. secalis or a mycelial plug of P. teres. Colony diameter for P. teres was monitored at 2, 4, and 7 days after inoculation. Sporulation was assessed after 7 days for P. teres and 14 days for R. secalis. The lowest concentration of glyphosate reduced in vitro sporulation of R. secalis by 60% compared with the untreated check. In contrast, glyphosate led to an increase in sporulation of P. teres at concentrations of 0.05–0.250 µL/mL with sporulation decreasing slightly when the concentration reached 0.500 µL/mL. There was a small reduction in P. teres colony growth at the higher concentrations of glyphosate.

Isolation of Fusarium graminearum from cereal, grass and corn residues from Alberta, 2001–2003

Abstract Fusarium species, which are typically associated with fusarium head blight of cereals, were isolated, identified and enumerated from residues collected in 239 cereal, 71 corn and 201 grass fields/sites in Alberta from 2001 to 2004. Cereal and grass residues were collected in the Peace River, central and southern regions of Alberta, while corn samples were collected from central and southern Alberta. The most frequently recovered species were F. avenaceum and F. culmorum followed by F. pseudograminearum and F. graminearum. Outside of southern Alberta, the most important causal agent of fusarium head blight, F. graminearum, was isolated at low levels in only one of 163 cereal fields, and was not isolated from the 39 corn fields or 105 grass sites surveyed. In contrast, in southern Alberta, F. graminearum was isolated from cereal residues in 10 of 76 cereal fields. Relatively high levels (46–50%) of node and crown infection occurred in one southern Alberta field in 2003. Fusarium graminearum was most common in corn residues from southern Alberta, being isolated from 24 of 32 fields, with average incidences of node infection ranging from 10 to 60% within these fields. In contrast, only three of 96 grass sites in southern Alberta had detectable, albeit low, levels of F. graminearum. The infrequent occurrence of F. graminearum, especially in central Alberta, and the Peace River region, suggests that Albertas agricultural industry should continue to monitor its presence in grain and crop residues, while attempting to limit further build up and spread of this pathogen.

Evaluation of a detached leaf assay to measure fusarium head blight resistance components in barley

Abstract Barley genotypes with known field reactions to fusarium head blight (FHB) were evaluated for partial disease resistance (PDR) components using an in vitro detached leaf assay. The detached leaves were inoculated with Fusarium graminearum or F. culmorum and incubated at room (21 ± 2 °C) or low temperature (10 ± 1 °C). Both species were pathogenic and had a shorter incubation period and produced larger lesions at room temperature. Inoculation with F. culmorum produced less well-delineated necrotic lesions compared with those from inoculation using F. graminearum under both temperature regimes. On susceptible genotypes, inoculation with F. graminearum at room temperature resulted in significantly shorter latent and incubation periods, larger lesions and more macroconidial production compared with resistant genotypes. Inoculation with F. culmorum resulted in no significant differences in any PDR components measured. Several PDR components for F. graminearum, including latent period, lesion size and macroconidial production, were found to be significantly correlated. There was a negative correlation between incubation period and field ratings in one of three tests, latent period and field ratings in two of three tests, and a positive correlation between lesion size and field disease severity ratings for FHB only in one of three tests. Few PDR components for F. culmorum were found to be significantly correlated with each other. Overall, the best differentiation between resistant and susceptible barley genotypes resulted from inoculation with F. graminearum at room temperature, including a significant correlation between incubation and latent periods with field ratings. In general, given the variability observed, especially in relation to field ratings for FHB, measurement of PDR components cannot be routinely used to complement field-based ratings. However, the measurement of latent period did show promise as it was correlated to field ratings in two of three tests and as such measurement of latent period may be useful in identifying genotypes highly susceptible or resistant to FHB. Further research is required to evaluate the potential of using a detached leaf assay to complement field screening for FHB resistance.

Interaction of net blotch and scald on barley

Abstract Net blotch caused by Pyrenophora teres f. sp. teres and scald caused by Rhynchosporium secalis are major foliar diseases of barley (Hordeum vulgare) and often occur together in the same fields in central Alberta, Canada. The differential development of these two diseases in relation to seeding date was investigated in five field trials in 2001 and 2003 under natural infection conditions. Significantly higher scald severity on barley was observed in all trials with early seeding (from early to mid May) as compared with late seeding (from late May to early June). Scald severity tended to be higher than net blotch severity in the early seeding date trials, whereas net blotch severity was generally higher than scald severity with late seeding. The differential development of disease severity between net blotch and scald was likely affected by temperature, host resistance, and natural inoculum. The interaction of the development of P. teres and R. secalis on barley ‘Harrington’ was investigated in artificially inoculated field plots in 1993 and 1995. In 1995, a mixture of both inocula induced a greater area under the disease progress curve (AUDPC) and caused a greater grain yield reduction than either inoculum alone in both seasons. No difference in grain yield was observed among plots in which P. teres or R. secalis were inoculated separately for either season. The disease progression and yield reductions observed in the present study indicate an additive effect as a result of the interaction between the two pathogens attacking the same plant. Early seeding of scald susceptible barley cultivars should be avoided in scald-infested fields in central Alberta. Scald susceptible cultivars may be seeded late for swath grazing of barley to escape scald infection.

Determining quantitative resistance of barley cultivars at the seedling stage to net blotch caused by Pyrenophora teres

Four barley (Hordeum vulgare L.) cultivars, Heartland, Harrington, Johnston, and Kasota, were compared a: the seedling stage for reactions to the net and spot forms of net blotch caused by Pyrenophora teres f. teres and P. teres f. maculata, respectively. Effects of leaf wetness period, leaf position, and inoculum concentration on lesion development were investigated. The linear relationship between inoculum concentration and diseased leaf area was used to estimate inoculum concentrations causing 50% diseased leaf area (ED50) on leaf 2 (the second seedling leaf) and causing 15% diseased leaf area (ED15) on leaf 3 (third seedling leaf). Resistance of cultivars was compared on the basis of ED50 and ED15. The linear relationship of diseased leaf area with time was used to estimate the rate of lesion spread and to compare resistance. Lack of a significant linear relationship over time on leaf 3 for cvs. Heartland and Kasota inoculated with P. teres f. teres reflected resistance in these two cultivars. Both pa...