The reactions of five double haploid lines of spring oilseed rape (Brassica napus) to 98 isolates of Leptosphaeria maculans, cause of blackleg, were tested in the greenhouse. The average of lesion lengths measured 3, 4, 5, 6, and 7 weeks after inoculation of stems of 5-week-old plants was used as a measure of virulence of isolates and of resistance of lines. Pearson and Spearman analyses showed that lesion lengths produced by isolates on pairs of lines were significantly correlated. This indicates that the relative virulence of an isolate was similar on all lines and the relative resistance of lines was similar for each isolate. It is concluded that field tests in which canola lines are exposed to natural inoculum of the fungus will generally provide reliable information on the resistance of the plant to naturally occurring populations of the fungus across a wider range of locations.

Diaporthe–Phomopsis complex, caused by Diaporthe phaseolorum var. caulivora, D. phaseolorum var. sojae, and Phomopsis longicolla, is an important disease complex of soybean (Glycine max) in Canada. To determine the predominant species of causal fungi in Ontario, 2700 pieces of stem tissue, 2700 pieces of pod tissue, and 9000 seeds from diseased plants were collected at nine locations each year from 2002 through 2004. In total, 17 280 isolates of the three pathogens were obtained from these plant parts over the 3 years, of which 73% were from stems, 23% from pods, and only 3% from seeds. Phomopsis longicolla was the predominant species (41% of isolates), followed by D. phaseolorum var. caulivora (37%) and D. phaseolorum var. sojae (22%). In total, 19 seed treatments consisting of various combinations of 10 formulated fungicides and two bioagents were evaluated at two sites each year from 2002 through 2004. Significant increases (P ≤ 0.05) in emergence and yield were observed for 8 and 2 of 11 seed treatments in 2002, 7 and none of 19 treatments in 2003, and all of 18 treatments in 2004, respectively. All 19 treatments in 2003 and 13 of 18 treatments in 2004 reduced root-rot severity. These treatments increased emergence by 2%–10% and yield by 7%–19%, and reduced root-rot severity by 20%–79%. ACM941 (Clonostachys rosea) + Apron Maxx RTA® (fludioxonil plus metalaxyl) was the only treatment that increased yield in 2 of the 3 years. Other treatments increased yield only in a single year. The results of this study provide evidence that fludioxonil, difenoconazole, triazolinthion, and trifloxystrobin protect soybean from seed-borne D. phaseolorum var . caulivora, D. phaseolorum var. sojae, and P. longicolla and increase plant emergence and yield, and that the effectiveness of these fungicides may be enhanced when they are used in combination with the bioagents. Key words: soybean, Glycine max, Diaporthe phaseolorum var . caulivora, Diaporthe phaseolorum var. sojae, Phomopsis longicolla, seed treatment. Au Canada, l'association Diaporthe-Phomopsis, constituée du Diaporthe phaseolorum var. caulivora, du D. phaseolorum var. sojae et du Phomopsis longicolla, est importante association de maladies sur le soja (Glycine max). À chaque année, entre 2002 et 2004, 2700 tissus pédonculaires, 2700 tissus de gousses et 9000 graines provenant de plantes malades furent récoltés à neuf endroits afin de déterminer l'identité des espèces prédominantes parmi les champignons causaux en Ontario. En 3 ans, un total de 17 280 isolats des agents pathogènes furent obtenus de ces parties de plante; de ceux-ci, 73 % provenaient de pédoncules, 23 % de gousses et seulement 3 % de graines. Le P. longicolla fut l'espèce prédominante (41 % des isolats), suivi du D. phaseolorum var. caulivora (37 %) et du D. phaseolorum var. sojae (22 %). De 2002 à 2004, un total de 19 traitements de semences, soit diverses combinaisons de 10 formulations de fongicides et de deux agents de lutte biologique, furent évalués à deux endroits à chaque année. Des augmentations significatives (P ≤ 0,05) de la levée et du rendement furent observées pour 8 et 2 des 11 traitements de semences en 2002, pour 7 et aucun des 19 traitements en 2003, et pour tous les 18 traitements en 2004, respectivement. Les 19 traitements en 2003 et 13 des 18 traitements en 2004 ont réduit l'intensité de la pourriture des racines. Ces traitements ont augmenté la levée de 2 % à 10 % et le rendement de 7 % à 19 %, et ont réduit l'intensité de pourriture des racines de 20 % à 79 %. Le traitement ACM941 (Clonostachys rosea) + Apron Maxx RTA® (fludioxonil plus métalaxyle) fut le seul qui augmenta le rendement lors de 2 des 3 années. D'autres traitements ont augmenté le rendement lors d'une seule année. Les résultats de la présente étude prouvent que le fludioxonil, le difénoconazole, le triazolinthion et la trifloxystrobine protègent le soja contre les D. phaseolorum var . caulivora, D. phaseolorum var. sojae et P. longicolla séminicoles et augmentent la levée et le rendement, et que l'efficacité de ces fongicides peut être améliorée lorsqu'ils sont combinés à des agents de lutte biologique. Mots-clés : soja, Glycine max, Diaporthe phaseolorum var . caulivora, Diaporthe phaseolorum var. sojae, Phomopsis longicolla, traitement de semences.

The effects of removing or flaming potato vines and soil fumigation on population density of Verticillium dahliae in soil, severity of Verticillium wilt, and tuber yield were studied in a field near Alliston, Ontario, between 1993 and 1996. Vines were physically removed or flamed using a propane flamer in September just before harvest and soil was fumigated with metam-sodium (Vapam) at 550 L/ha in October after harvest. Vine removal had no effect on soil populations of V. dahliae , area under the disease progress curve (AUDPC), or tuber yield. Flaming once (1993), twice (1993 and 1994), or three (1993,1994, and 1995) times reduced the soil population density of V. dahliae , and flaming twice (1993 and 1994) reduced AUDPC compared to the nontreated control, but had no effect on tuber yield. Fumigation once (1993) or twice (1993 and 1994) reduced pathogen density in soil and AUDPC, but did not increase tuber yield. Fumigation once (1993) or twice (1993 and 1994), in combination with flaming twice (1993 and 1994), was equally and significantly effective in reducing both population density of V. dahliae in soil and AUDPC values and in increasing tuber yield in 1995. Annual flaming of vines in combination with soil fumigation once (1993) or twice (1993 and 1994) in the fall improved the control of Verticillium wilt of potato and realised the greatest profits.

Populations of Phytophthora infestans , causing late blight of potato, changed significantly in Canada in the mid-1990s. The US-1 genotype (A1, metalaxylsensitive [MS]) was displaced by novel genotypes (mainly US-8) in much of the country in 1994 and 1995. Many of the new genotypes were insensitive to metalaxyl and were of the A2 mating type, although metalaxyl-insensitive (MI) Al isolates of the gll (or US-11) genotype were found in British Columbia. A total of 14 unique multilocus genotypes were described over the two years of the study based on mating type (Al or A2), metalaxyl sensitivity (MS or MI), allozyme banding patterns ( Gpi and Pep ), and random amplified polymorphic DNA (RAPD) markers. Six of these genotypes could be distinguished by allozyme banding patterns at the Gpi locus alone; RAPD analysis revealed additional variation within allozyme groupings and defined additional genotypes. Among 82 isolates collected from various Canadian provinces in 1994, US-1 and US-8 constituted 30% and 49% of isolates, respectively; other genotypes occurred in minor frequency. Among 50 isolates collected in 1995, US-1 and US-8 constituted 10% and 74%, respectively. Isolates of gll (US-11) were found in British Columbia in 1995. Diversity of genotypes was greater in 1994 (11 genotypes) than in 1995 (six genotypes). We hypothesize that sexual reproduction may have been responsible for generating some of the genetic variability in P. infestans populations, during a time period in which A2 isolates first migrated into many provinces in Canada.

Survival of asexual (sporangia and mycelium) propagules of Phytophthora infestans in autoclaved peat moss exposed to various temperatures was assessed by ability to infect floating potato leaf discs. Infectivity of propagules in peat was measured after 0, 21, 35, 63, and 79 days of exposure to temperatures ranging from -33 C to 20 C. Propagules exposed to temperatures below freezing were no longer infective after 21 days. Exposure of propagules to temperatures of 15 or 20 C resulted in a rapid decline in infectivity over time; by the final sampling date, none were infective. In contrast, propagules exposed to a temperature of 5 C for 79 days remained infective.

Studies were conducted in 1995, 1996, and 1997 to determine the ability of Canadian isolates of Phytophthora infestans to cause tuber disease in a variety of potato cultivars. Most isolates of recently introduced multilocus genotypes (US-7, US-8, g11, g26, g29, and g40) were more aggressive on tuber tissue than isolates of the traditional US-1 genotype, based on surface necrosis (SN), lesion depth (LD), and compound aggressiveness index (CAI = SN × LD) components. Other multilocus genotypes (g30, g41, g42, and UN-3) were similar in aggressiveness to US-1. The g11 (US-11) genotype consistently displayed aggressiveness that was intermediate to that of the US-8 and US-1 genotypes. Variation also occurred within a multilocus genotype, and an isolate of the US-8 genotype from New Brunswick was consistently less aggressive than other US-8 isolates. Cvs. Dorita and Island Sunshine were consistently the most resistant to infection, regardless of isolate, relative to the more susceptible responses of Green Mountain, Russet Bur-bank, Kennebec, Superior, Shepody, Red Pontiac, Sebago, and Bintje. Even so, isolates of the newly introduced US-8 genotype were able to cause significantly more disease on these resistant cultivars than isolates of the US-1 genotype. The predominant genotypes currently found in potato production areas in Canada (US-8 and g11) have higher fitness on tuber tissue than displaced, preexisting strains (US-1).

A collection of 80 isolates of Phytophthora infestans, representing multilocus genotypes of the pathogen found in Canada from 1994 to 1996, was screened on a series of nine differential potato host cultivars to determine the physiological race of the isolates. A total of 28 pathotypes were found among the 11 genotypes present in the collection. There was a significant increase in the complexity of pathotypes from 1994 to 1996 which reflected the displacement of the US-1 genotype (mean of 2.2 host differentials infected) by the US-8 genotype (mean of 8.1 host differentials infected). Eighteen of the US-8 isolates could overcome all nine of the resistance genes tested. Virulence genes which overcame host resistance conferred by R8 were the rarest in the populations studied. The predominance of complex populations of P, infestans in Canada implies that the introduction of cultivars with specific R genes for resistance would be an ineffective control measure.

The prevalence, incidence, and severity of fungal infections of the lower stem, crown, and roots of winter wheat in 105-109 fields in 11 counties of southwestern Ontario during July of 1985 and 1986 were determined in relation to precipitation, temperature, crop history, tillage practices, and soil pH and fertility. Fusarium avenaceum and F. acuminatum occurred in 85-96% of the fields and infected 14-28% of the crowns. Fusarium culmorum and F. graminearum were less abundant, occurring in about 50% of the fields, and in 3-7% of the crowns. Take-all [Gaeumannomyces graminis var, tritici] occurred in 65-93% of the fields and in 25-28% of the plants. It affected 8-12% of the stem and root surface on average. Eyespot [Pseudocercosporella herpotrichoides] occurred in 40-54% of the fields and on 5-10% of the stems. Sharp eyespot [Rhizoctonia cerealis] occurred in 4-22% of the fields and on 2-3% of the stems. Average daily temperature was negatively correlated with the incidence of F. avenaceum, eyespot and sharp eyespot, and positively correlated with the incidence of F. acuminatum. Frequency of grass or cereal in the rotation was positively correlated with the incidence of F. avenaceum and the severity of take-all. No other significant and consistent correlations were observed between infection and environmental or cultural parameters. The significance of these results is discussed in relation to control and natural regulation of these infections.

A collection of 80 isolates of, representing multilocus genotypes of the pathogen found in Canada from 1994 to 1996, was screened on a series of nine differential potato host cultivars to determine the physiological race of the isolates. A total of 28 pathotypes were found among the 11 genotypes present in the collection. There was a significant increase in the complexity of pathotypes from 1994 to 1996 which reflected the displacement of the US-1 genotype (mean of 2.2 host differentials infected) by the US-8 genotype (mean of 8.1 host differentials infected). Eighteen of the US-8 isolates could overcome all nine of the resistance genes tested. Virulence genes which overcame host resistance conferred by R8 were the rarest in the populations studied. The predominance of complex populations of in Canada implies that the introduction of cultivars with specific R genes for resistance would be an ineffective control measure.

Pathogenicity and random amplified polymorphic DNA (RAPD) markers were used to assess genetic diversity among 93 highly virulent isolates of Leptosphaeria maculans (Desm.) Ces. & de Not. collected from two oilseed rape (Brassica napus L.) fields located 20 km apart in southern Ontario. Using three differential host cultivars of B. napus (Westar, Quinta, and Glacier), isolates were separated into three pathogenicity groups (PG). Eighty percent of the isolates were in PG4, virulent on all cultivars, and 11% were in PG3, virulent on two cultivars. The remaining 9% were tentatively placed into a new PG, PG5, because they showed intermediate virulence on the three cultivars. There was no relationship between RAPD pattern and either PG or isolate collection site. Cluster analysis of RAPD patterns, based on estimates of genetic distance, grouped isolates into two populations, corresponding to the field of collection. Analysis of molecular variance attributed 45.5% of the total variance to differences between populations and 54.5% to differences among isolates. Every isolate was genetically distinct, suggesting that the populations of the fungus were produced mostly by sexual reproduction. We conclude that inoculum in the two fields consisted principally of ascopores, derived almost equally from sources that were common to both fields and sources that were distinct for each field. Key words: highly virulent, Leptosphaerla maculans, random amplified polymorphic DNA (RAPD), genetic variation.

The distribution of the highly virulent and weakly virulent types ofLeptosphaeria maculans, causal agent of blackleg of oilseed rape, was studied in two fields in southern Ontario. Using a polymerase chain reaction-based assay with primers specific for these virulence types, plant tissues were directly examined for the occurrence of the pathogen. The highly virulent type was detected in leaf, stem and crown tissue at most of the sampling sites. The weakly virulent type was detected only in leaf lesions at 50% of the sites in field 1 and 30% of the sites in field 2. Of 96 leaf lesions examined, 48 contained the highly virulent type, 12 contained the weakly virulent type and 16 contained both the highly virulent and weakly virulent types.Sclerotinia sclerotiorum was isolated from all leaf lesion that did not react withL. maculans virulence type-specific primers. Coinfection of single blackleg leaf lesions by bothL. maculans virulence types thus occurred in oilseed rape plants in the field. Only the highly virulent type was detected in pseudothecia on stubble. Approximately 1% of the seed collected from these two fields containedL. maculans, and both the highly virulent and weakly virulent types were detected. The highly virulent type was more prevalent and non-specific in the kind of plant tissue it infected, whereas the weakly virulent type appeared to be limited to infecting leaves and seed. This study illustrates an application of polymerase chain reaction with virulence type-specific oligonucleotide primers to study the epidemiology of blackleg of oilseed rape.

Disease incidence, disease severity, areas under the disease incidence and disease severity progress curves, and maximum and minimum incidence and severity of disease were evaluated as measures of resistance in canola (Brassica napus) to blackleg caused by Leptosphaeria maculans. Seven genotypes of spring canola were tested in Ontario at three locations 60, 81, and 102 days after sowing in 1990 and at two locations 55, 70, 85, and 100 days after sowing in 1991. Disease incidence was expressed as the percentage of sampled plants with basal stem canker, and disease severity was assessed as the percentage discolouration of a cross section of the stem base. Based on ease of measurement, range of values, number of significant differences among genotypes, and constancy of rank of genotypes at different locations, measures of disease severity or disease incidence in mature plants proved to be most useful. No advantage was gained by using area under the disease incidence and disease severity progress curves, or maximum and minimum incidence and severity of disease at the last sampling time. It is recommended that resistance of canola stems to blackleg be evaluated from measures of disease severity or disease incidence in mature plants. Keywords: canola, blackleg, Leptosphaeria maculans, resistance measurements.

Development of blackleg on oilseed rape plants (Brassica napus) after artificial contamination of seed with Leptosphaeria maculans was studied in field plots during 1991-1992. Incidence of contaminated seed at sowing was correlated with incidence of plants with stem lesions, incidence of plants with crown canker, severity of crown canker, and incidence of infected seed at harvest. In four trials, the ratio of diseased plants 56-120 days after sowing to the incidence of contaminated seed ranged from 26% to 333%. Between sowing and harvest (98-107 days), blackleg spread as far as 216 cm from contaminated seed. It was estimated that a seed lot containing 1% contaminated seed could give rise to crown cankers in 3.3% of the plants, widespread distribution of diseased plants in the field, and yield losses of 1-2%.

The interaction between highly virulent (HV) and weakly virulent (WV) isolates ofLeptosphaeria maculanson oilseed rape leaves was examined. In the growth room, leaves of the susceptible cultivar Westar were inoculated with HV and WV isolates together, a HV isolate followed, up to 6 days later, by a WV isolate, or a WV isolate followed, up to 6 days later, by a HV isolate. Both the HV and WV types were detected by PCR in lesions produced by all of these co-inoculations. Isolates from these lesions also yielded colonies of both types. The size of lesions produced by the HV type was reduced if the WV type was introduced at the same time as the HV type. Inoculation with the WV type less than 48h after the HV type also significantly reduced lesion diameter caused by the HV type, but no reduction in lesion size occurred if the WV type was added 64h or later after the HV type. Lesions caused by inoculation with the WV type followed by the HV type were also significantly smaller than those caused by the HV type alone. Maximum reduction in the size of the lesion occurred when the HV type was inoculated 24h or later after the WV type. Inoculation of the second true leaf with the WV type significantly reduced the size of lesions produced by the HV type elsewhere on the same leaf, on neighbouring leaves, and in the stem. We conclude that the WV type can coinfect and coexist with the HV type within a single lesion in leaves and inoculation of the WV type can induce systemic acquired resistance (SAR) in oilseed rape to the HV type. This is the first report of SAR in oilseed rape.

A review of four comprehensive sources of information reveals that cultural practices, i.e. practices not employing host resistance, pesticides, or specific biological control agents, are important to the management of all of the 50 principal diseases of common bean (Phaseolus vulgaris) and essential to the control of 40. Thirty-one groups of cultural practices contribute to the control of bean diseases. The practices most frequently recommended are rotation, pathogen-free seed, weed control, and tillage. The number of cultural practices recommended per disease ranges from 1 to 15. Several precepts relating to the development and rational use of cultural practices in bean disease control are derived from this quantitative analysis. Control of diseases through cultural practices is essential to sustainable bean health.

All of 57 commercial fields of winter oilseed rape (Brassica napus) examined in 1990 and 1991 in Ontario exhibited symptoms of blackleg caused by Leptosphaeria maculans. Average severity of crown canker on a scale of 0-4 was 1.7 in 1990 and 2.6 in 1991. The fungus infected all of 41 seed samples collected in these two years. The average and maximum annual incidences of infected seed per sample were in the ranges 0.9-1.5% and 3.6-5.1%, respectively. Of 61 isolates of L. maculans obtained from seed, 50 were highly virulent and ii were weakly virulent. The incidence of infected seed at harvest was correlated with disease severity on pods in 1990 and on crowns in 1991. Correlations between severity and incidence of crown canker and between severity of pod lesions and incidence of plants with pod lesions were obtained in both years. Several other measures of disease were correlated only in 1991. This is the first report for Ontario of infection of seed of oilseed rape by L. maculans and of correlations among seed infection and disease parameters. The relevance of the results to management of blackleg is discussed.

Of 92 isolates of Leptosphaeria maculans from six countries, 68 contained a single isozyme of glucose phosphate isomerase (GPI) that moved 70 mm after 11 h of starch gel electrophoresis and 24 contained a single isozyme of GPI that moved 65 mm. Isolates with fast or slow isozymes of GPI were classified as electrophoretic type (ET) 1 or 2, respectively. The mean lesion length produced by ET2 isolates inoculated into stems of canola (double haploid plants derived from Brassica napus cv. Westar) differed significantly from that of ET1 isolates. However, lesion lengths of the most virulent of the ET2 isolates and of the least virulent of the ET1 isolates were not significantly different and cluster analysis of lesion lengths did not separate the collection of isolates into two groups coincident with electrophoretic type. Similarly, neither optical density nor pH of spent culture medium divided the isolates into two distinct groups. Only GPI isozyme polymorphisms separated the collection unequivocally into two groups, ET1 and ET2, which had the general characteristics of the highly virulent and weakly virulent strains of L. maculans.