H. D. Voldeng

Biological control of fusarium head blight of wheat with Clonostachys rosea strain ACM941

Fusarium head blight (FHB), caused by Gibberella zeae, is a devastating disease of wheat. A strain of Clonostachys rosea, ACM941 (American Type Culture Collection ATCC 74447), was evaluated for antibiosis against G. zeae in vitro and for control of FHB under greenhouse and field conditions in comparison to the registered fungicide Folicur (tebuconazole). Strain ACM941 reduced mycelial growth of the pathogen by 52.6% in dual-culture after 6 days and completely suppressed spore germination for 6 h when cocultured with a macroconidial suspension of G. zeae. Strain ACM941 reduced G. zeae perithecial production by more than 99% in a leaf disk assay, 60%–77% on infected corn kernels, and 32%–57% on spikelet debris in the field. These effects were significant (P < 0.05) and not statistically different from those produced by tebuconazole. When strain ACM941 was sprayed onto wheat heads 2 days prior to inoculation with G. zeae, it significantly reduced infected spikelets (IS) by 64% and Fusarium -damaged kernels (FDK) by 65% in greenhouse experiments. Under simulated disease epidemic conditions during 2005–2007, strain ACM941 reduced the FHB index by 58%, IS by 46%, FDK by 49%, and deoxynivalenol (DON) in kernels by 21%. These effects were significant but lesser in magnitude than those achieved by tebuconazole, which reduced FHB index by 97%, IS by 82%, FDK by 73%, and DON by 62%. Results from this research suggest that strain ACM941 of C. rosea is a promising biocontrol agent against G. zeae and may be used as a control measure in an integrated FHB management program.

Comparative aggressiveness of isolates of Fusarium spp. causing head blight on wheat in Canada

Fusarium head blight (FHB) is an important disease of wheat in Canada. To supplement the development of FHB-resistant cultivars, the aggressiveness of Fusarium isolates representing eight species was investigated. Six wheat lines and cultivars were artificially inoculated with 12 isolates of F. graminearum and 6 isolates each of F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. poae, and F. sporotrichioides at 50% anthesis. Symptoms of FHB were rated as disease severity on a 0 to 9 scale, 4, 7, 14, 21, and 28 days after inoculation, and as percentage of infected spikelets (IS) after 21 days. All species caused visible infections to the wheat lines and cultivars, but only F. graminearum, F. crookwellense, and F. culmorum resulted in severe disease development (>35% IS) and were considered highly pathogenic while the remaining species, which had <15% IS, were moderately and weakly pathogenic. There were significant differences (P < 0.05) in aggressiveness among isolates within species and in susceptibility among wheat lines and cultivars, suggesting that screening for resistance to FHB requires a mixture of several isolates. A new technique for a rapid and mass production of conidial spores of Fusarium spp. was described. This is also the first report showing that F. crookwellense is highly pathogenic to wheat.

Evaluation of the pathogenicity of Fusarium graminearum and Fusarium pseudograminearum on soybean seedlings under controlled conditions

Fusarium graminearum, the cause of fusarium head blight of small-grain cereals and of gibberella ear rot of corn, has recently been reported to attack soybean, causing root rot and pod blight. A morphologically similar species, Fusarium pseudograminearum, is also an important pathogen of the roots and crown of cereals, but its pathogenicity against soybean has not been tested yet. Pathogenicity tests were conducted under controlled conditions to compare aggressiveness within and between isolates of F. graminearum and F. pseudograminearum in causing root rot of soybean. In each experiment, agar plugs (2 mm in diameter) from 7-day-old fungal cultures were placed on the primary root at the VE (vegetative emergence) growth stage. Twenty seedlings of each of three soybean cultivars were inoculated separately with six isolates each of the two Fusarium spp. All isolates caused visible infection 10 d after inoculation, but F. graminearum isolates were significantly more aggressive than those of F. pseudograminearum. The two species caused average disease severities of 2.3 and 1.1, reduced shoot lengths by 28.9% and 6.9%, and reduced plant dry masses by 12.8% and 7.9%, respectively. Significant differences (P < 0.05) were found among cultivars for all parameters and among isolates of F. graminearum in disease severity and shoot length, but there were no significant cultivar × isolate interactions. Further research is needed to verify, in soybean, genotypic difference and possible resistance to the two species.

Biological management of Fusarium head blight and mycotoxin contamination in wheat

Fusarium head blight (FHB), caused by Gibberella zeae is a harmful disease of wheat. To manage FHB and mycotoxin contamination in wheat, field experiments were conducted from 2007 to 2008 to evaluate a total of 20 selected bioagents for their ability to inhibit perithecial production of G. zeae and for the control of FHB and deoxynivalenol (DON) contamination, in comparison with the registered fungicide Folicur (tebuconazole). All 20 bioagents significantly reduced the perithecial production compared to the untreated control. Clonostachy rosea strain ACM941 was the most effective treatment, reducing the production of perithecia by 63.7% in 2007 and 67.5% in 2008. These effects were significantly better than Folicur fungicide, which reduced perithecial production by 30.4% and 20.5%, for 2007 and 2008, respectively. When sprayed on to wheat heads, seven of the 20 bioagents significantly reduced the FHB index, one reduced Fusarium damaged kernels (FDK), and six reduced DON content in grains in 2007. ACM941 w...

Comparison of the influence of inoculum sources on the development of fusarium head blight and the deoxynivalenol content in spring wheat in a disease nursery

The screening for genetic resistance to fusarium head blight (FHB) in wheat has been challenged by the lack of efficacy of various artificial inoculation techniques in disease nurseries. In 2001-2003, we examined the influence of inoculum sources (conidial suspension, infested barley and corn kernels, or infested wheat debris) and inoculation frequency on the development of FHB and the deoxynivalenol (DON) content. The study was conducted on three spring wheat genotypes in a disease nursery of Ottawa, Ontario. The development of FHB was monitored by visually estimating disease severity on a scale of 0 to 9, six times during each growing season. Severity of FHB over time was summarized as the area under the disease-progress curve (AUDPC). Symptoms of FHB were also rated, at a critical developmental stage (soft dough), as critical-time disease severity (DS), percentage of infected spikelets (IS), and FHB index. The percentage of Fusarium-damaged kernels (FDK) and DON content in the wheat kernels were assessed after harvesting. All inoculation treatments had significantly greater AUDPC and DS in 2002, FHB index and IS in 2001 and 2002, and FDK in all three years than the noninoculated control. Regardless of inoculum source, two inoculations produced as much FHB, FDK, and DON as three inoculations. Among the inoculum sources, the conidial suspension or infested kernels yielded significantly greater AUDPC, DS, FHB index, IS, and DON content than the infested debris. Inoculation with conidial suspension resulted in greater FDK than inoculation with infested kernels or infested debris, between which there were no differences. The results of the present study confirm that conidial suspension and infested kernels are equally effective inoculants for FHB nurseries. Infested debris, though a natural source of inoculum, is less effective.

Effect of seed treatments on emergence, yield, and root rot severity of soybean under Rhizoctonia solani inoculated field conditions in Ontario

Field trials were conducted with soybean at two sites each year from 2001 to 2003 in Ottawa, ON, to determine the effect of seed treatments with various combinations of seven formulated fungicides and the bioagent Yield Shield (Bacillus pumilus GB34) under Rhizoctonia solani inoculated conditions. Controls were untreated seed planted into both non-inoculated (natural) soil and soil inoculated with R. solani. Compared with the non-inoculated control, inoculation significantly increased root rot severity and reduced emergence by 27%, and yield by 31%. Under the inoculated conditions, none of the seed treatments significantly increased emergence or yield in all of the six trials when compared with the control. Allegiance (metalaxyl) plus Vitaflo-280 (carbathiin plus thiram) and Vitaflo-280 alone were the most effective seed treatments, increasing emergence in by 20 and 19% and yield by 21 and 26%, which were significantly better than the control in four and five trials for emergence and three and four trials...

Efficacy of CLO-1 biofungicide in suppressing perithecial production by Gibberella zeae on crop residues

Abstract Fusarium head blight (FHB), caused by Gibberella zeae (anamorph: Fusarium graminearum), is a destructive disease of cereals. Previous studies demonstrated that Clonostachys rosea strain ACM941 is an antagonist of G. zeae that parasitizes the pathogen and reduces FHB severity in wheat. The objective of this research was to evaluate the efficacy of CLO-1, a formulated product of ACM941, for reducing perithecial production on various crop residues in comparison with the registered fungicide Folicur (tebuconazole) under field conditions. When applied on G. zeae inoculated corn, soybean and wheat residues in the spring of 2009 and 2010, CLO-1 significantly inhibited perithecial production on all crop residue types, reducing daily perithecial production (DPP) by 93.1% on corn residue, 94.4% on soybean residue and 84.0% on wheat residue, compared with the untreated control. When applied on naturally infected wheat residues in the autumn of 2009 and 2010, CLO-1 significantly reduced DPP in the following growing season by 72.3% on peduncles, 51.0% on spikelets and 57.2% on stems. These effects were numerically better but not significantly different from those achieved by Folicur fungicide used as a positive control in the same experiments. Results from this study suggest that CLO-1 is a promising biofungicide against G. zeae and may be used as a control measure to reduce the initial inoculum of FHB in an integrated FHB management programme.

A retrospective look at short-season soybean cultivar development in Ontario

Cober, E. R. and Voldeng, H. D. 2012. A retrospective look at short-season soybean cultivar development in Ontario. Can. J. Plant Sci. 92: 1239-1243. Canadian soybean production has increased from about 63 000 ha in 1951 to 1.2 million ha in 2006 with expansion from southern Ontario to shorter season areas. From 1971 to 2000, soybean production in Ontario increased sixfold. Using annual reports from 1971 to 2000 of short-season trials in Ontario, we found that the number of reported cultivars remained between three and five until 1984 when the number of cultivars started to increase at the rate of about 2.5 yr-1. The amount of time that cultivars remained in the reports has declined from 12 to 4 yr on average over the 30-yr period. Long-lived cultivars, however, were developed throughout the period including: Hardome, Merit, Evans, Maple Arrow, Bicentennial, Maple Glen, KG 41, OAC Eclipse, 9071, OAC Bayfield, PS 36, and S03-W4. Over the 30-yr period of cultivar testing, short-season seed yield increased about 600 kg ha-1, while mean time to maturity decreased about 10 d. During the same time, mean Ontario commercial seed yields increased about 750 kg ha-1. Over the 30-yr period, the number of short-season cultivars in annual reports increased 36-fold, while provincial yield increased only 1.4-fold. If the number of cultivars in annual reports is an indication of breeding effort, large research investments may be necessary to increase future yield improvement.

AC COLIBRI SOYBEAN

AC Colibri is a 2500 heat unit soybean (Glycine max [L.] Merr.) cultivar developed for natto soyfood production. Key words: Soybean, cultivar description, natto

CROP MANAGEMENT EFFECTS ON FUSARIUM HEAD BLIGHT, FUSARIUM-DAMAGED KERNELS AND DEOXYNIVALENOL CONCENTRATION OF SPRING WHEAT

Proper crop management is an important strategy in reducing Fusarium head blight (FHB) and deoxynivalenol (DON) concentrations in spring wheat (Triticum aestivum). A field study was conducted for three growing seasons to investigate FHB severity, Fusarium-damaged kernels (FDK), and DON concentrations and their inter-relationships as affected by planting and harvesting dates and nitrogen application. Cultivar ‘AC Brio’ was planted on three dates at approximately 10-d intervals starting from the last week of April. Five nitrogen (N) treatments were 0, 60 and 100 kg N ha−1 applied as starter, 60 (starter) + 40 kg N ha−1 as top-dress and 60 + 40 kg N ha−1 foliar spray at boot stage. Later planting increased FDK and DON concentration and the effects were greater in coarse-textured than in a fine-textured soil. DON concentration sometimes doubled when harvest was delayed after physiological maturity. Nitrogen treatments per se had no effects on FDK and DON.