Francisco Zamudio

The use of linear mixed model theory for the genetic analysis of repeated measures from clonal tests of forest trees. I. A focus on spatially repeated data

The paper reviews the linear mixed models (LMM) methodology that is suitable for the statistical and genetic analyses of spatially repeated measures collected from clonal progeny tests. For example, we consider a poplar clonal trial where progenies of different families are propagated by cuttings, and only one ramet per clone is planted on each block. Modeling covariance structures following the LMM theory allows improving genetic parameter estimation based on clonal testing. Besides variance components, we also obtained an estimate of the covariance between residuals (within clonal effects in two different blocks). This covariance is due to planting more than one ramet from the same genotype in the same trial, which generates correlated residual effects from different blocks. Its estimation can significantly improve the comparison among clones within a progeny test or between tests in a clonal testing network. Results indicate that the covariance is also a component of the genetic variance estimator and plays a significant role in assessing the variance of specific (micro) environmental effects. A positive covariance implies that ramets show a similar performance in more than one block. Thus, a larger and more positive covariance implies a stronger genetic effect controlling the expression of the trait in the local environment and a smaller variance of specific environmental effects. On the contrary, a negative covariance implies that the performance of individual ramets is affected by strong microenvironmental effects, specific to one or more blocks, which can also directly increase the within-clone variability.

Susceptibilidad de híbridos de Populus spp. al ataque de áfidos y roya en tres localidades de Chile

En los ultimos anos se ha generado un creciente interes en el potencial forestal de las especies e hibridos del genero Populus (alamos) en Chile. Sin embargo, algunas plagas y patogenos atacan severamente a estas plantaciones. Con el fin de identificar algunos hibridos resistentes (o menos susceptibles) a estas plagas, se evaluo la susceptibilidad de algunos taxones de Populus spp. al ataque del afido Chaitophorus leucomelas y al hongo Melampsora spp. El estudio se realizo en tres localidades del centro-sur de Chile. Los resultados revelan que la densidad de afidos fue mayor en marzo, particularmente en Coinco (region de O’Higgins) y menor en Pillanlelbun (region de Los Rios) y Yumbel (region del Biobio). En Pillanlelbun el taxon mas susceptibles a afidos correspondio a TD×TD [ (P. trichocarpa x P. deltoides) x (P. trichocarpa x P. deltoides)] y los menos susceptibles fueron TD×D [ (P. trichocarpa x P. deltoides) x P. deltoides], T×N (P. trichocarpa x P. nigra), TMxTM [(P. trichocarpa x P. maximowitzii) x (P. trichocarpa x P. maximowitzii)] y TD×T [ (P. trichocarpa x P. deltoides) x P. trichocarpa]. Las infecciones con Melampsora spp. se presentaron en orden decreciente en Coinco, Yumbel y Pillanlelbun. El taxon T×N fue el mas susceptible a roya en las tres regiones, mientras que los menos susceptibles fueron TD×T, TD×D y TD×T. Estas susceptibilidades variaron entre localidades, principalmente para afidos. No hubo correlacion entre la abundancia de C. leucomelas y de Melampsora spp. Se discuten los factores geneticos y ambientales que podrian explicar estos resultados.

Within-crown acclimation of leaf-level physiological and morphological parameters in young loblolly pine stands

Key messageLight plays a minor role in the within-crown acclimation of physiological and morphological parameters in small loblolly pine trees.AbstractWhether the plasticity of foliage within the crown is driven by light or height is still not well known, especially for small trees. The present study was conducted in two loblolly pine (Pinus taeda L.) stands growing on two sites, during the third year after planting. The following traits were investigated in the lower and upper crowns of the same individuals twice per season (spring, summer, and autumn): photosynthesis (Asat), stomatal conductance (gs), intrinsic water use efficiency (WUEint), nitrogen concentration ***(N), specific leaf area (SLA), photosynthetic nitrogen use efficiency (PNUE), fascicle diameter, and needles per fascicle. The trees were open-grown at the beginning of the study; thus, any vertical gradient of the traits was not assumed to be driven by light. Overall, Asat, gs, PNUE, and SLA tended to be higher in the lower than in the upper crown, whereas N, fascicle diameter, and needles per fascicle were higher in the upper than in the lower crown. However, although all traits were affected by crown position, the magnitude of this effect differed by season. The fact that crown position affected most of the traits in spring and summer, but not in autumn, suggest that height might be the main driver of foliage acclimation. However, considering that crown position affected SLA in autumn but not the photosynthetic rate or N concentration, it is possible that foliar acclimation of these traits was mainly driven by light in this season.

Variabilidad genética del crecimiento en progenies selectas de Pinus radiata .

Narrow sense heritability (h 2 ), intra-class genetic correlations (G 2 IC ) and variance components for height, diameter at breast height and stem volume of seven-year-old trees were investigated. Two progeny trials of Pinus radiata were planted in southern Chile and growth data obtained to estimate genetic variability. These trials included trees from vegetative and generative propagation. Generative propagated trees were used to estimate the heritability, which indicated the following values: height, 0.08-0.13; stem diameter, 0-0.13; stem volume, 0-0.09. Estimates of intra-class genetic correlations among groups of trees from vegetative propagation were moderate to low (G 2 IC at 7 years of age: height, 0.1-0.11; stem diameter, 0.01-0.05; stem volume, 0.03-0.06). The relatively limited variation between trees groups was expected, reflecting the strong selection applied. In general, trees from cuttings displayed a tendency to have a smaller intra-genotypic variation, and a greater among groups variances (s 2 g ) than family variances (s 2 f ), in four out of six traits evaluated. This indicated a tendency for a greater homogeneity in growth, as is common in vegetatively propagated plants.