Effect of foliar applications of a calcium-based formulation on the antioxidant systems of soybeans affected by Sclerotinia sclerotiorum. A. ARFAOUI, A. EL HADRAMI AND F. DAAYF. Department of Plant Science, 222 Agriculture Building, University of Manitoba, Winnipeg, MB R3T 2N2, Canada; and (A.A., A.E.H.) OMEX Agriculture Inc., 290 Agri Park Road, Oak Bluff, MB R4G 0A5, Canada
White mould [Sclerotinia sclerotiorum (Lib.) de Bary] is a devastating plant pathogen in a variety of crops in Canada. Different control strategies are necessary to keep the disease under an economical threshold. The aim of this research was to evaluate the effect of calcium-based formulation applications on the antioxidative reactions in soybeans affected by a highly or a weakly aggressive isolate of S. sclerotiorum. Changes were assessed at 1, 2, 4, 8, 24, 48 and 72 h after inoculation. Generation of hydrogen peroxide, superoxide and hydroxyl radicals was evaluated. The activity of several antioxidant enzymes was monitored, including catalase, guaiacol peroxidase, ascorbate peroxidase, reduced glutathione and glutathione transferase. Results show that soybeans expressed an early oxidative burst followed by the activation of various antioxidant systems in response to infection. Much more delay was observed in response to the highly as compared with the weakly aggressive isolate. The application of calcium based-formulation two days before inoculation induced significant increases in the activity of several defence-related enzymes, suggesting an involvement of calcium in reducing the progress of this disease.
Pseudomonas sp. DF41 biological control – keeping fungi and bacterial predators at bay. T. R. DE KIEVIT, M. NANDI, A. K. BRASSINGA, P. C. LOEWEN AND W. G. D. FERNANDO. Department of Microbiology and (W.G.D.F.) Department of Plant Science, 222 Agriculture Building, 66 Dafoe Road, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
Pseudomonas sp. DF41 is a rhizosphere isolate able to protect canola from the devastating effects of Sclerotinia stem rot. A lipopeptide (LP) called sclerosin is essential for DF41 inhibition of Sclerotinia sclerotiorum (Lib.) de Bary. Structural analysis revealed sclerosin to be a novel compound that resembles corpeptins produced by the mushroom pathogen Pseudomonas corrugata. The primary mode of action of LPs is through pore formation in target membranes. Application of sclerosin to ascospores and mycelia of S. sclerotiorum completely inhibited germination, indicating this compound targets different forms of the pathogen. To be effective, a biocontrol agent must be able to sustain itself in the environment. Bacteria are constantly at risk of protozoan predation; therefore, we investigated how production of compounds, including sclerosin affects DF41 interaction with the bacterial-feeder Caenorhabditis elegans. When a panel of DF41 mutants were fed to worms, a mutant no longer producing sclerosin and hydrogen cyanide became the preferred food source. Moreover DF41 is able to form a thick coating, called a biofilm, over the worm surface preventing feeding and effectively starving the worm. Thus production of toxic compounds and biofilm formation may enable DF41 to escape predation in the environment, allowing for more effective biocontrol.
Microsatellite markers reveal two distinct genetic groups of the late blight pathogen, Phytophthora infestans, in Manitoba. M. R. ISLAM, H. ALKHER, C. GODEE, M. BEZZAHOU, L. R. ADAM, L. M. KAWCHUK, K. F. DOBINSON, K. L. CONN, R. D. PETERS, K. I. AL-MUGHRABI, T. SHINNERS-CARNELLEY and F. DAAYF. Department of Plant Science, 222 Agriculture Building, 66 Dafoe Road, University of Manitoba, Winnipeg, MB R3T 2N2, Canada; (L.M.K.) Lethbridge Research Centre, Agriculture and Agri-Food Canada (AAFC), 5403 1st Avenue South, Lethbridge, AB T1J 4B1, Canada; (K.F.D., K.L.C.) Southern Crop Protection and Food Research Centre, AAFC, 1391 Sandford Street, London, ON N5V 4T3, Canada; (R.D.P.) Crops and Livestock Research Centre, AAFC, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada; (K.I.A.-M.) Potato Development Centre, New Brunswick Department of Agriculture, Aquaculture and Fisheries, 39 Barker Lane, Wicklow, NB E7L 3S4, Canada; and (T.S.-C.) Peak of the Market, P.O. Box 2032, Carman, MB R0G 0J0, Canada
Late blight caused by the oomycete pathogen, Phytophthora infestans (Mont.) de Bary, is one of the most destructive diseases of potato and tomato worldwide. An increased frequency of late blight epidemics has been reported, in parallel with changes in the population structure of this pathogen in North America and elsewhere. During the mid-1990s, the US-1 genotype was displaced by its US-8 counterpart, which rapidly became the most dominant genotype and remained so until 2007 in Canada. In Canada, new outbreaks of late blight on both potato and tomato during 2009–2012 were caused by new P. infestans genotypes such as US-22, US-23 and US-24. In Manitoba, P. infestans isolates collected in 2010–2012 were of the A1 mating type, showed a wide range of responses to metalaxyl irrespective of genotypes and were of Ia mitochondrial DNA (mt-DNA) haplotype. The restriction fragment length polymorphism (RFLP) analysis in 2010 revealed a mixture of both US-23 and US-24 genotypes in the population. In 2011, US-24 emerged as a dominant genotype as opposed to 2012 where US-23 became dominant. We further used 34 P. infestans isolates collected from all 3 years in Manitoba to investigate the genetic structure of these populations using microsatellite markers. A reasonable number of simple sequence repeat (SSR) motifs were observed in both genotypes with an average of two (range two–three) alleles per locus. Cluster analyses based on 11 recently developed microsatellite markers differentiated US-24 and US-23 genotypes in two distinct clusters.
Breeding for stem rust [Puccinia graminis f. sp. tritici] resistance in barley (Hordeum vulgare) at the AAFC Brandon Research Centre – future directions. J. R. TUCKER, W. G. LEGGE, A. BADEA AND T. G. FETCH JR. Brandon Research Centre, Agriculture and Agri-Food Canada (AAFC), 2701 Grand Valley Road, Brandon, MB R7A 5Y3, Canada; and (T.G.F.) Cereal Research Centre, AAFC, 195 Dafoe Road, Winnipeg, MB R3T 2M9, Canada
Stem rust [Puccinia graminis Pers. f. sp. tritici Eriks. & Henn.] epidemics on the Canadian prairies have been effectively controlled in barley (Hordeum vulgare) using a single, dominant gene (Rpg1) since the 1950s. In 1989, a virulent race (QCCJ) was detected in North Dakota, USA. This prompted the establishment of a large QCCJ stem rust nursery at Agriculture and Agri-Food Canada (AAFC) Brandon. Numerous populations were developed using the resistant lines PI 382313 (Rpg3) and Q21861 (rpg4/ Rpg5). In 1999, a new virulent race (TTKSK or Ug99) was detected in Uganda, which has since evolved into multiple variants and spread throughout several countries in Africa and the Middle East. Genetic analysis has revealed that the presence of two separate but closely linked genes (rpg4 and Rpg5) is required to confer resistance to QCCJ or TTKSK. Breeding lines have been evaluated in a Plant Pest Containment Level 3 (PPC3) facility at AAFC Morden and in field nurseries at Njoro, Kenya, Africa. Preliminary results suggest that some of the germplasm previously developed for resistance to the QCCJ race may also be resistant to TTKSK and could be useful as parents. Future efforts at AAFC Brandon will include: re-establishment of a QCCJ stem rust nursery to screen breeding lines, confirmation of resistance in selected lines to TTKSK and/or lineage variants using the PPC3 laboratory and field nurseries in Africa, and use of biotechnological tools such as molecular marker assisted selection combined with doubled haploidy to accelerate development of resistant barley germplasm.