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Grass weed competition with bread wheat in Ethiopia: I. Effects on selected crop and weed vegetative parameters and yield components Tessema, Taye; Tanner, D.G. & Hulluka, Mengistu Abstract Competition effects of four of the predominant grass weed species in Ethiopia (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), and Phalaris paradoxa L.) on the morphological characters, grain yield, and yield components of bread wheat (Triticum aestivum L.) were studied in western Shewa Zone of Ethiopia. The four grass species varied significantly in their effects on wheat plant height, tillering, leaf area index (LAI), number of fertile spikes m-2, grains per spike, spike length, thousand grain weight, straw, biomass, harvest index and grain yield. A. abyssinica and S. polystachya were the most competitive, reducing wheat morphological characters and yield components to a greater extent than L. temulentum and P. paradoxa. The reduction in wheat grain yield was linearly proportional to the square root of weed seedling density. Grass species by seedling density interaction effects were significant for most of the crop and weed characters measured, indicating a differential rate response for individual species. The reduction in wheat grain yield at the maximum weed density of 320 seedlings m-2 ranged from 48 to 86% across the four grass species studied. The wheat yield components most affected by weed competition were number of fertile spikes m2 and number of seeds/spike. Weed vegetative and reproductive characters (i.e., number of tillers, LAI, number of panicles, and plant height) varied markedly among species and in direct proportion with weed seedling density. Plant height and LAI appeared to be the factors most closely associated with weed competitive ability with bread wheat. Keywords Competition, grass weeds, wheat, yield components

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Tessema, Taye; Tanner, D.G. & Hulluka, Mengistu Résumé Les effets de competition de quatre des predominantes especes d'adventices en Ethiopie (Avena abyssinica Hoechst, Lolium temulentum L., Snowdenia polystachya Fresen (Pilg), et Phalaris paradoxa L.) sur les caracteres morphologiques, le rendement en grain, et les composantes du rendement du ble (Triticum aestivum L.) etaient etudies dans la zone ouest de Shewa en Ethiopie. Les effets des quatre especes d'herbes variaient considerablement sur la hauteur du ble, le tallage, l'indice de surface foliaire, le nombre d'epis fertiles m-2, les grains par epi, la longueur de l'epi, le poids de mille grains, la paille, la biomasse, l'index de recolte et le rendement en grain. A. abyssinica et S. polystachya etaient les plus competitifs, reduisant grandement les caracteres morphologiques et les composantes du rendement en ble que L. temulentum et P. paradoxa. La reduction du rendement en grain de ble etait linealrement proportionnelle a la racine carree du taux de germination des adventices. Les effets d'interaction du taux de germination des especes d'herbes etuient signicatifs pour la plupart des characteres mesures sur la culture et sur les adventices, indiquant une difference de taux de reponse par espece individuelle. La reduction du rendement en grain du ble a la densite maximale des adventices de 320 plantes m-2 variait de 48 a 86 % autour des quatre especes d'herbes etudiees. Les composantes du rendement en ble les plus affectees par la competition des adventices flaient le nombre d'epis fertiles m2 et le nombre de graines/epi. Les caracteres vegetatifs et reproductifs des adventices (le nombre de tailes, l'indice de surface foliaire, le nombre de panicules, et la hauteur de la plante) varialent remarquablement parmi les especes, et en proportion directe avec le taux de germination des adventices. La hauteur de la plante et l'indice de surface folialre sont apparus etre les facteurs les plus etroitement associes avec l'habilite de competition des adventices avec le ble. Mots Clés Adventices, ble, competition, composantes du rendement

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