Pulse crops (annual grain legumes such as field pea, lentil, dry bean, and chickpea) have become an important component of the cropping system in the northern Great Plains of North America over the last three decades. In many areas, the intensity of damping-off, seedling blight, root rot, and premature ripening of pulse crops is increasing, resulting in reduction in stand establishment and yield. This review provides a brief description of the important pathogens that make up the root rot complex and summarizes root rot management on pulses in the region. Initially, several specific Fusarium spp., a range of Pythium spp., and Rhizoctonia solani were identified as important components of the root rot disease complex. Molecular approaches have recently been used to identify the importance of Aphanomyces euteiches on pulses, and to demonstrate that year-to-year changes in precipitation and temperature have an important effect on pathogen prevalence. Progress has been made on management of root rot, but more IPM tools are required to provide effective disease management. Seed-treatment fungicides can reduce damping-off and seedling blight for many of the pathogens in this disease complex, but complex cocktails of active ingredients are required to protect seedlings from the pathogen complex present in most commercial fields. Partial resistance against many of the pathogens in the complex has been identified, but is not yet available in commercial cultivars. Cultural practices, especially diversified cropping rotations and early, shallow seeding, have been shown to have an important role in root rot management. Biocontrol agents may also have potential over the long term. Improved methods being developed to identify and quantify the pathogen inoculum in individual fields may help producers avoid high-risk fields and select IPM packages that enhance yield stability.

Aphanomyces root rot (ARR), caused by Aphanomyces euteiches Drechs., is a destructive soilborne disease of eld pea (Pisum Sativum L.). No completely resistant pea germplasm is available, and current ARR management strategies rely on partial resistance and fungicidal seed treatments. In this study, an F 8 recombinant inbred line (RIL) population of 135 individuals from the cross 'Reward' (susceptible) × '00-2067' (tolerant) was evaluated for reaction to ARR under greenhouse conditions with the A. euteiches isolate Ae-MDCR1 and over 2 years in a eld nursery in Morden, Manitoba. Root rot severity, foliar weight, plant vigor and height were used as estimates of tolerance to ARR. Genotyping was conducted with a 13.2K single-nucleotide polymorphism (SNP) array and 222 simple sequence repeat (SSR) markers. Statistical analyses of the phenotypic data indicated signi cant (P<0.001) genotypic effects and signi cant G×E interactions (P<0.05) in all experiments. After ltering, 3050 (23.1%) of the SNP and 30 (13.5%) of the SSR markers were retained for linkage analysis, which distributed 2999 (2978 SNP + 21 SSR) of the markers onto nine linkage groups representing the seven chromosomes of pea. Mapping of quantitative trait loci (QTL) identi ed 5 major-effect (R 2 > 20%), 13 moderate-effect (10%

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2007. Sensitivity of field populations of Ascochyta rabiei to chlorothalonil, mancozeb, and pyraclostrobin fungicides, and effects of strobilurin fungicides on the progress of ascochyta blight of chickpea. Can. J. Plant Sci. 87: 937-944. Chickpea production faces a major challenge from ascochyta blight (Ascochyta rabiei), a devastating disease that can cause total crop loss. To assess the effect of repeated fungicide application on disease progress, strobilurin fungicides, primarily alternating pyraclostrobin and azoxystrobin treatments, were applied up to five times per year in each of 2 yr. A single application or two early applications reduced blight severity. A third application resulted in additional benefits in 1 of 2 yr, but additional applications did not reduce severity further. To monitor for fungicide tolerance in populations of A. rabiei, 66 single-spore isolates were collected and grown on growth media amended with chlorothalonil, mancozeb, or pyraclostrobin. Insensitivity to one or more of the fungicides was detected in 49 (74%) of the isolates. Based on the effect on conidial germination, insensitivity to pyraclostrobin or chlorothalonil was observed in 26 of 37 isolates (70%). Repeated fungicide application may be selecting for insensitive isolates of the pathogen; fungicide application should be combined with cultural measures to control ascochyta blight. des populations naturelles de Ascochyta rabiei au chlorothalonil, au mancozèbe et à la pyraclostrobine, et incidence des fongi-cides à la strobilurine sur la progression de la brûlure ascochytique chez le pois chiche. Can. J. Plant Sci. 87: 937-944. La brûlure ascochytique (Ascochyta rabiei), maladie dévastatrice pouvant détruire complètement une culture, pose un sérieux prob-lème aux producteurs de pois chiches. Afin d'évaluer l'incidence d'un usage répétitif de fongicide sur la progression de la mal-adie, les auteurs ont appliqué des fongicides à la strobilurine, principalement de la pyraclostrobine et de l'azoxystrobine en alternance, jusqu'à cinq fois par année pendant deux ans. Une seule application ou deux applications précoces de fongicide atténu-ent la gravité de la maladie. Une troisième application a eu des effets bénéfiques additionnels une année mais pas l'autre. Les applications supplémentaires n'ont pas réduit la gravité de la maladie davantage. Pour déterminer la tolérance de A. rabiei aux fongicides, les auteurs ont recueilli 66 isolats d'une spore qu'ils ont cultivés sur un milieu de croissance contenant du chlorothalonil, du mancozèbe ou de la pyraclostrobine. Quarante-neuf (74 %) des isolats étaient insensibles à un ou à plusieurs fongicides. D'après la germination des conidies, on a décelé l'insensibilité à la pyraclostrobine ou au chlorothalonil chez 26 des 37 isolats (70 %). L'application répétitive de fongicide pourrait favoriser la sélection d'isolats insensibles du pathogène; il con-viendrait de combiner le traitement antiparasitaire à des méthodes de lutte culturales pour combattre la brûlure ascochytique.

. 2000. Effect of temperature, seeding date, fungicide seed treatment and inoculation with Fusarium avenaceum on seedling survival, root rot severity and yield of lentil. Can. J. Plant Sci. 80: 899-907. Early seeding of lentil is necessary on the northern prairies to ensure that the crop has time to mature. However, planting into cold soils in spring results in slow germination, which may predispose seedlings to infection by soil-borne pathogens. In a controlled-environment study of the impact of temperature on infection of lentil seedlings (cv. Eston) by Fusarium avenaceum, root rot symptoms were most severe at warm temperatures (20°to 27.5°C) and declined in warmer or cooler soils. Field plots were seeded on three dates, which were spaced about 2 wk apart between early May and early June in four station years. Seedling emergence was most consistent and seed yield was highest in three of four sites at the second seeding date. Emergence and yield were substantially lower for the latest seeding date. Inoculation with F. avenaceum reduced establishment and seed yield. Seed treatment with Crown (thiabendazole and carbathiin) improved seedling survival, reduced root rot severity and increased seed yield relative to the inoculated control. Vitaflo-280 (thiram and carbathiin) also improved establishment and yield, but the effect was not as strong or consistent. Treatment with Raxil (tebuconazole) and Apron (metalaxyl) had no effect. The pathogenicity of aggressive isolates of F. avenaceum from lentil on a range of crop species was evaluated. All crops were susceptible to some degree, which indicates that the pathogen, once established, is likely to persist in a field for some time. This study demonstrated that early planting was required for maximum yield, that certain isolates of F. avenaceum were pathogenic on a wide range of hosts, and that seed treatment can be used to minimize losses from seedling blight and root rot in lentil. Dans la partie nord des Prairies, la lentille doit être semée de bonne heure au printemps si on veut qu'elle ait le temps de mûrir. Cependant, son installation dans les sols froids ralentit la germination, exposant les jeunes plantes à l'infection par les pathogènes telluriques. Dans le cadre de travaux en milieu contrôlé sur les effets de la température sur l'infection des plantules de lentille, cultivar Eston, par Fusarium avenaceum, les symptômes de pourridié les plus graves étaient observés sous régime de températures chaudes (20 à 27,5°C) et perdaient de leur intensité au-dessus ou en dessous de cet écart. Des parcelles expérimentales étaient semées au champ à quatre années-stations (1996-1998) à trois dates, échelonnées à environ deux semaines d'intervalle entre le début de mai et le début de juin. Le taux de levée le plus stable et le rendement grainier le meilleur étaient obtenus à 3 des 4 emplacements pour la deuxième date de semis, mais les valeurs de ces deux paramètres étaient nettement plus basses pour la dernière date de semis. L'inoculation de F. avenaceum provoquait une réd...

. 2003. Etiology, impact and control of rhizoctonia seedling blight and root rot of chickpea on the Canadian Prairies. Can. J. Plant Sci. 83: 959-967. Studies were undertaken to assess the impact of seedling blight and root rot caused by Rhizoctonia solani AG-4 on nodulation and seed yield of chickpea. The effects of pathogen inoculum concentration and seed damage on disease severity were also measured. Chickpea seedlings were grown under controlled-environment conditions in sterilized soil amended with pathogenic isolates of R. solani and in field plot experiments where the inoculum was incorporated with the seed at planting. In greenhouse experiments, emergence and dry matter production declined and root rot severity increased with increasing inoculum concentration. Root rot reduced nodulation where lesions covered more than 25% of the root surface. For chickpea cultivar Sanford this level of infection was sufficient to reduce root mass, but for the cultivar Tyson, more than half of the root was covered with lesions before root mass began to decline. In a comparison of seed treatment fungicides, thiram + carbathiin (Vitaflo 280) and carbathiin + thiabendazole (Crown at 6 mL of product kg -1 seed) significantly increased seedling emergence and seed yield compared to the inoculated control. In an assessment of the effects of seed damage, seedling survival and seed yield were similar for both healthy and mechanically damaged seed. Rhizoctonia solani has the potential to be an important constraint to chickpea production in the prairie region of western Canada. 83: 959-967. Les auteurs ont essayé d'évaluer l'incidence de la brûlure et du piétin causés par Rhizoctonia solani AG-4 sur la nodulation et le rendement grainier du pois chiche. Ils ont aussi déterminé dans quelle mesure la gravité de la maladie était influencée par la concentration de l'inoculum pathogène et les graines abîmées. Les plantules de pois chiche ont été cultivées en milieu contrôlé, dans du sol stérilisé auquel on a ajouté un isolat pathogène de R. solani, et sur des parcelles expérimentales, au sol desquelles on a incorporé l'inoculum avec la graine, à la plantation. Lors des expériences en serre, l'usage d'un inoculum de plus en plus concentré entraîne une baisse du taux de levée et de la production de matière sèche ainsi qu'une hausse de la gravité du piétin. Le piétin réduit la nodulation quand les lésions couvrent plus de 25 % de la surface des racines. Avec le cultivar Sanford, ce degré d'infection suffit à réduire la masse des racines, mais avec de Tyson, cette dernière ne diminue que lorsque plus de la moitié des racines sont couvertes de lésions. Lors d'un essai comparatif sur les fongicides destinés aux semences, l'usage de thiram + carbathiin (Vitaflo 280) et de carbathiin + thiabendazole (Crown, à raison de 6 ml par kg de semences) entraîne une hausse sensible du taux de levée et du rendement grainier par rapport au témoin inoculé. En ce qui concerne les graines endommagées, le taux de survie des plantules et le rendement grainier r...