Miguel J. Arturi

Genetic variability in natural populations of Paspalum dilatatum Poir. analyzed by means of morphological traits and molecular markers.

Native species show adaptive traits that are difficult to find in introduced species. The Pampas region in Argentina is a valuable nature reserve of grasses and Paspalum dilatatum Poir. is one of the most important grasses found there. Based on ploidy level and on morphological traits, five biotypes of P. dilatatum have been described. Two of them were included in this study: a tetraploid biotype with sexual reproduction and a pentaploid biotype with apomictic reproduction. We analyzed the genetic diversity in eight native populations from the Salado basin, Argentina, using both quantitative traits and molecular data (RAPD) with these aims: to obtain information of the degree of phenotypic variation in that area, to know which the pattern of distribution of this variation is and to look for association between molecular markers with populational or biotypic differentiation. Cluster analysis based on morphological data grouped the individuals of the different populations by ploidy level. Molecular markers showed the inverse situation because individuals were grouped by geographic origin as opposed to biotype. Moreover, since RAPD did not discriminate between biotypes with sexual or apomictic reproduction, they are probably not associated with mating system. The results let us conclude that polygenic traits such as LP, LBSR, NRT and NSP can discriminate between biotypes and molecular markers such as bands 12, 40, 19 and 46 can be used to discriminate among populations, probably because they detect neutral variation.

Phenotypic diversity in Argentinian populations of Bromus catharticus (Poaceae). Genetic and environmental components of quantitative traits

Abstract Genetic and environmental components were analysed in 32 Argentinian populations of Bromus catharticus. The research was based on 39 vegetative and reproductive characters. Constancy (rc) and heritability (h2) ratios were calculated. ANOVAS showed differences between populations for 14 traits, most of them reproductive. Total phenotypic variation was mostly due to the environmental component. Microfloral attributes showed the highest values of rc and h2. The traits average length of the spikelets (LS), average number of florets per spikelet (NFS), and lemma length (LL), which simultaneously reach rc values higher than 1 and h2 values higher than 0.60, could be considered useful in systematic studies. Leaf, stem, and some reproductive characters, linked to propagule production, had plastic responses. However, traits associated with size and shape of propagules and spikelets remained constant. Results suggest that a double strategy is operating: plasticity in some traits (to give greater adaptability), and constancy in other traits related to species stability that are of systematic significance.

VARIABILIDAD FENOTÍPICA Y GENÉTICA EN POBLACIONES DE PASTO MIEL (Paspalum dilatatum Poir.)

El pasto miel (Paspalum dilatatum Poir.), es una graminea perenne de ciclo estival y alto valor forrajero. El objetivo de este trabajo fue obtener estimaciones de la variabilidad fenotipica y genetica entre y dentro de poblaciones del biotipo dilatatum. Se tomaron muestras extrayendo plantas completas en tres sitios del sector norte de la Depresion del Salado (La Plata, Magdalena y Pereyra Iraola) en la provincia de Buenos Aires, Argentina. El material, mantenido en envases plasticos, fue utilizado para medir seis caracteres: numero de nudos por macolla (NNM), largo y ancho de lamina de la hoja bandera (LLHB y ALHB), largo del raquis de la espiga basal (LREB), numero de espigas por panoja (NEP), y numero de semillas por espiga basal (NSEB). De las 18 comparaciones entre medias de las tres poblaciones (prueba de t), siete mostraron diferencias significativas al nivel p = 0,01 y seis al nivel p = 0,05. La varianza fenotipica dentro de las poblaciones contuvo, en promedio, 26% de varianza genetica, con un rango de grado de determinacion genetica (GDG) desde 0 a 52%. Se deduce de esos resultados que la variabilidad intrapoblacional no supero la variabilidad entre poblaciones. Si bien los resultados de GDG no son altos, debido al sistema de reproduccion apomictica, la totalidad de la variacion genetica disponible podria ser utilizada con fines de mejoramiento. El analisis de componentes principales dio resultados coincidentes con la prueba de t, siendo los caracteres NNM, LLHB, LREB, y NSEB los de mayor poder discriminatorio.