The field performance of the native Pappophorum vaginatum, the naturalized Eragrostis curvula and various cultivars of the introduced Achnatherum hymenoides and Leymus cinereus was evaluated as potential forage resources in rangelands of arid Argentina during the warm seasons of 2007/2008 and 2008/2009. Plants of these grass species, obtained from seeds, were transplanted to the field in 2006, when they were 1 year old. During the study years, there were two defoliation managements: plants of all study genotypes either remained undefoliated (controls) or were defoliated twice a year during spring at 5 cm stubble height. Despite tiller number being lower (P < 0·05) on defoliated than on undefoliated plants, and total leaf length per unit basal area being similar (P > 0·05) between defoliation managements by mid‐spring, there were no differences (P > 0·05) in dry weight production between defoliated and undefoliated plants in all genotypes at the end of the second growing season. Plants of one or more of the introduced genotypes showed a similar (P > 0·05) or greater (P < 0·05), but not lower, tiller number per plant and per square centimetre, daughter tiller production, total leaf length and dry weight production per unit basal area than the native species at the end of the first and/or second growing seasons. These morphological variables were similar (P > 0·05) or greater (P < 0·05) in the native than in the naturalized genotype. Plant survival, however, was lower (P < 0·05, overall mean = 20%) in the introduced than in the native (>70%) or naturalized (>39%) genotypes at the end of the first or second growing seasons.
Our objectives were to (1) determine the effects of light on seed germination of 2 populations (P1, P2) of Pappophorum vaginatum, and (2) compare the germination responses between these populations. Because of this, two studies were conducted. The first study evaluated the effects of 2 light conditions (L0=darkness, and L1=14 h light) on the cumulative germination (%) after 4, 8, 15 and 19 days from imbibition. The second study was conducted only under L1 conditions, and it evaluated the (a) cumulative germination, (b) germination speed index, (c) time to 50% of cumulative germination (T50), (d) percentage of empty spikelets (i.e., without cariopsis), and percentage spikelets with imbibed, but not germinated cariopsis after 19 days from imbibition of seeds. Pappophorum vaginatum was the dominant species in both study communities, but total, live plant cover was 37.5% in community 1, and 62.5% in community 2. Both populations were sensitive to light. After 19 days from imbibition there was a significant, positive effect of light on cumulative germination. In the second study, cumulative germination and germination speed index were greater (p≤0.01) in P1 than in P2. At the same time, T50 and the percentage of spikelets with imbibed, but not germinated cariopsis, were greater (p≤0.01) in P2 than in P1; no differences were found in the percentage of empty spikelets. Our results demonstrated that light was important for seed germination in P. vaginatum, and that the timing for initiating germination as a response to light differed between the two study P. vaginatum populations.KEY wORDS: germination, Pappophorum vaginatum, populations, light effects, natural reseeding, establishment, perennial grasses RESUMENNuestros objetivos fueron (1) determinar el efecto de la luz en la germinación de dos poblaciones (P1, P2) de Pappophorum vaginatum, y (2) comparar las respuestas de la germinación entre estas poblaciones. Se condujeron dos estudios. El primer estudio evaluó los efectos de dos condiciones de luz (L0=oscuridad, y L1=14 h de luz) en la germinación acumulada (%) después de 4, 8, 15 y 19 días desde la imbibición. El segundo estudio solo se condujo bajo las condiciones L1, y se evaluaron (a) la germinación acumulada, (b) el índice de velocidad de germinación, (c) el tiempo al 50% de germinación acumulada (T50), (d) el porcentaje de espiguillas vacías (sin cariopse), y el porcentaje de espiguillas con ca-
En Argentina, más específicamente en los pastizales del sur de la provincia fitogeográfica del Monte, Pappophorum vaginatum Buckley es prácticamente la única especie que provee forraje para los animales durante el verano. Debido a esto, se necesitan estudios orientados a lograr la mejora genética en esta especie que combine los efectos de la selección natural en el ambiente local y los de la selección artificial para caracteres de interés agronómico, especialmente los vinculados al control de la implantación y a la producción de forraje y semillas. Los objetivos de este estudio fueron determinar (a) los componentes de la varianza y coeficientes de variación (a nivel fenotípico, genotípico y ambiental), y (b) la heredabilidad en sentido amplio para varios caracteres de interés agronómico vinculados a la implantación, y la producción de forraje y semillas en cuatro poblaciones espontáneas de Pappophorum vaginatum recolectadas en la región semiárida de la provincia de Buenos Aires. También se observaron asociaciones entre dichos caracteres. Según la población, resultaron significativos (p?0,05) del análisis de varianza entre 6 y 12 de los 14 caracteres de interés agronómico estudiados para cada una de las poblaciones, con valores altos de heredabilidad y una relación superior a 1 entre el coeficiente de variación genético y el coeficiente de variación ambiental. Esto muestra que las expectativas de lograr algún avance genético en un programa de selección de Pappophorum vaginatum serían promisorias para varios caracteres de interés agronómico, inclusive en el corto plazo.
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