Engineered glyphosate resistance is the most widely adopted genetically modified trait in agriculture, gaining widespread acceptance by providing a simple robust weed control system. However, extensive and sustained use of glyphosate as a sole weed control mechanism has led to field selection for glyphosate-resistant weeds and has induced significant population shifts to weeds with inherent tolerance to glyphosate. Additional weed control mechanisms that can complement glyphosate-resistant crops are, therefore, urgently needed. 2,4-dichlorophenoxyacetic acid (2,4-D) is an effective lowcost, broad-spectrum herbicide that controls many of the weeds developing resistance to glyphosate. We investigated the substrate preferences of bacterial aryloxyalkanoate dioxygenase enzymes (AADs) that can effectively degrade 2,4-D and have found that some members of this class can act on other widely used herbicides in addition to their activity on 2,4-D. AAD-1 cleaves the aryloxyphenoxypropionate family of grass-active herbicides, and AAD-12 acts on pyridyloxyacetate auxin herbicides such as triclopyr and fluroxypyr. Maize plants transformed with an AAD-1 gene showed robust crop resistance to aryloxyphenoxypropionate herbicides over four generations and were also not injured by 2,4-D applications at any growth stage. Arabidopsis plants expressing AAD-12 were resistant to 2,4-D as well as triclopyr and fluroxypyr, and transgenic soybean plants expressing AAD-12 maintained field resistance to 2,4-D over five generations. These results show that single AAD transgenes can provide simultaneous resistance to a broad repertoire of agronomically important classes of herbicides, including 2,4-D, with utility in both monocot and dicot crops. These transgenes can help preserve the productivity and environmental benefits of herbicide-resistant crops.herbicide resistance | weed management | genetically modified crops |

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Ascochyta rabiei (teleomorph Didymella rabiei) is a directly penetrating, necrotrophic fungus that infects all aboveground parts of chickpea (Cicer arietinum). During spore germination and infection, germ tubes secrete a mucilaginous substance to facilitate attachment to the host surface, and the invading fungus produces cell-wall-lytic enzymes to penetrate the host. The pathogen produces several phytotoxins (solanapyrones A, B, and C, cytochalasin D, and a proteinaceous toxin) that seem to be responsible for necrosis and cell death. The pathogen can degrade antimicrobial compounds and suppress their production in chickpea. On the basis of aggressiveness, the population of A. rabiei can be classified into two broad pathotypes: pathotype I (less aggressive) and pathotype II (aggressive). Complete resistance to A. rabiei has not been found in chickpea; the resistance present in superior cultivars used in chickpea production is partial or incomplete. There is a high degree of variation in resistance among chickpea cultivars, and the resistance declines as the plant matures. The symptoms of infection and disease severity follow a quantitative continuum based on aggressiveness of the pathogen, genetic resistance present in the cultivar, and age of the plant. The well-established defense responses in chickpea are cross-linking of cell walls mediated by hydrogen peroxide, production of pathogenesis-related (PR) proteins (chitinase, β-1,3-glucanase, and thaumatin-like proteins), and accumulation of phytoalexins. However, expression of these induced defense responses does not correlate with pathotype-specific resistance, indicating that other constitutive or unknown components may be involved in providing resistance to aggressive pathotypes. Lack of information about the attribute that makes the pathogen aggressive, as well as inadequate knowledge of pathotype-specific defense mechanisms and the causes for decline in resistance, are major constraints in developing cultivars with durable resistance. 509Résumé : L'Ascochyta rabiei (téléomorphe Didymella rabiei) est un champignon nécrotrophe à pénétration directe, capable d'infecter toutes les parties aériennes du pois chiche (Cicer arietinum). Lors de la germination des spores et de l'infection, les tubes germinatifs sécrètent une substance mucilagineuse qui facilite la fixation à la surface de l'hôte, et le champignon envahisseur produit des enzymes lytiques de la paroi cellulaire pour pénétrer dans l'hôte. Le champignon pathogène produit plusieurs phytotoxines (solanapyrones A, B et C, cytochalasine D et une toxine protéique) qui semblent responsables de la nécrose et de la mort des cellules. Le champignon pathogène peut dégrader des substances antimicrobiennes et inhiber leur production dans le pois chiche. En fonction de l'agressivité, la population de l'A. rabiei peut être classée en deux grands pathotypes : le pathotype I (moins agressif) et le pathotype II (agressif). On n'a pas trouvé de résistance complète à l'A. rabiei dans le pois chiche; la résistance présente c...

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. 2006. Selection for seed size and its impact on grain yield and quality in kabuli chickpea. Can. J. Plant Sci. 86: [345][346][347][348][349][350][351][352]. Seed cost is a major input expense for the production of kabuli chickpea (Cicer arietinum L.) due to its large seed size. Use of small seeds could reduce production costs because a lower volume of seeds would be needed per unit area. This study determined the effects of seed size, and selective use of small seeds, year after year, on the field performance of kabuli chickpea in Swift Current, Saskatchewan from 2000 to 2003. Separated large (9.1-11.0 mm diameter) and small (8.1-9.0 mm) seeds of certified CDC Xena were compared with the original, unseparated seeds during the 4-yr study period. Also, small seeds separated from small-seeded previous crops and large seeds separated from large-seeded previous crops were compared with the respective generations of unseparated seeds. Year significantly affected plant biomass, seed yield, and the proportion of ≥ 9-mm-diameter seeds (9DSeeds) in the harvested seed lot, and crops grown from large and small seeds separated from the original seed lot (i.e., 1st year of separation) did not differ in a given year. The 2nd year of selection for small seeds affected seed yield and 9DSeeds, although the effect was minimal. With 3 consecutive years of selection, small seeds lowered seed yield by 23% and decreased 9DSeeds by 10% compared with the unseparated seeds. Selective use of large seeds improved biomass, but did not increase seed yield or 9DSeeds compared with the unseparated seeds. Small seeds of a certified kabuli cultivar can be selectively used for up to 2 consecutive years before incurring a yield penalty, but the use of small seeds will decrease the percentage of large seeds in the harvested seed lot. . L'utilisation de graines plus petites réduirait les coûts de production, car il faudrait moins de semences par unité de surface. La présente étude devait établir les effets du calibre des graines et de l'usage sélectif de petites graines, une année après l'autre, sur le rendement au champ du pois chiche kabuli, à Swift Current (Saskatchewan), de 2000 à 2003. Pendant les quatre années qu'a durées l'expérience, les auteurs ont comparé l'usage de grosses (9,1 à 11,0 mm de diamètre) et de petites (8,1 à 9,0 mm) graines certifiées de la variété CDC Xena aux semences originales non triées. Ils ont aussi trié les petites graines des cultures à petites semences antérieures et les grosses graines des cultures à grosses semences antérieures afin de les comparer aux générations issues des semences non triées. L'année affecte de manière significative la biomasse de la plante, le rendement grainier et la proportion de semences ≥ 9 mm de diamètre (graines9D) dans le lot de graines récoltées; les grosses et les petites graines venant du lot original (à savoir, première année de tri) ont donné des résultats analogues d'une année à l'autre. La deuxième année, la sélection des semences les plus petites a affecté le rendement et la p...