Summary
Native fungi of West Africa were evaluated as a means to control Striga hermonthica (Del.) Benth., a troublesome parasitic weed of several gramineous crops. An isolate of Fusarium oxysporum, grown on sorghum straw and incorporated into pots, successfully prevented all emergence of S. hermonthica, and resulted in a 400% increase of sorghum dry weight. The fungus inhibited germination and attachment of S. hermonthica to sorghum roots in Plexiglas root chambers. Several crop species, including sorghum, inoculated with the fungus showed neither any disease symptoms nor any reduction in biomass.
Various crops were evaluated in 3-year rotation sequences for their ability to reduce population densities of the potato root-lesion nematode, Pratylenchus penetrans, and improve subsequent potato (Solanum tuberosum) yield in field microplots. Forage and grain pearl millets (Pennisetum glaucum) were evaluated against oats (Avena sativa), Indian mustard (Brassica juncea), soybean (Glycine max), rye (Secale cereale), potato, and corn (Zea mays). Population densities of P. penetrans were high under rye, potato, oats, and Indian mustard and low under both forage and grain pearl millets. A single year of grain pearl millet after two consecutive years of potato or rye significantly reduced P. penetrans populations compared with 3 years of potato or rye and two consecutive years of corn, Indian mustard, oats, or soybean. One year of forage or grain pearl millet prior to potato decreased P. penetrans populations below the damage threshold of 1000 kg -1 of soil. The subsequent potato crop produced the highest marketable and total yields following either three consecutive crops of forage or grain pearl millet or a single crop of forage or grain pearl millet preceded by rye or soybean. Total yields of potato 'Superior' were significantly negatively correlated with soil densities of P. penetrans in both fall 2002 (P < 0.001, r = -0.539) and spring 2003 (P < 0.001, r = -0.423). Both forage pearl millet 'CFPM 101' and the grain pearl millet hybrid 'CGPM H-1' have potential for the magagement of P. penetrans in Quebec's potato-production system.
Lettuce is a major vegetable crop worldwide that is affected by numerous bacterial pathogens, including Xanthomonas hortorum pv. vitians, Pseudomonas cichorii, and Pectobacterium carotovorum. Control methods are scarce and not always effective. To develop new and sustainable approaches to contain these pathogens, we screened more than 1,200 plant-associated Pseudomonas strains retrieved from agricultural soils for their in vitro antagonistic capabilities against the three bacterial pathogens under study. Thirty-five Pseudomonas strains significantly inhibited some or all three pathogens. Their genomes were fully sequenced and annotated. These strains belong to the P. fluorescens and P. putida phylogenomic groups and are distributed in at least 27 species, including 15 validly described species. They harbor numerous genes and clusters of genes known to be involved in plant-bacteria interactions, microbial competition, and biocontrol. Strains in the P. putida group displayed on average better inhibition abilities than strains in the P. fluorescens group. They carry genes and biosynthetic clusters mostly absent in the latter strains that are involved in the production of secondary metabolites such as 7-hydroxytropolone, putisolvins, pyochelin, and xantholysin-like and pseudomonine-like compounds. The presence of genes involved in the biosynthesis of type VI secretion systems, tailocins, and hydrogen cyanide also positively correlated with the strains’ overall inhibition abilities observed against the three pathogens. These results show promise for the development of biocontrol products against lettuce bacterial pathogens, provide insights on some of the potential biocontrol mechanisms involved, and contribute to public Pseudomonas genome databases, including quality genome sequences on some poorly represented species.
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