Relationships among productivity determinants in two hybrid poplar families grown during three years at two contrasting sites.
ABSTRACT The objective of this study was to evaluate the environmental, temporal and genetic stability of the relationships between growth and a selection of tree architectural, leaf and phenological traits (selection based on the conclusions of previous studies carried out on the same experimental trial). Therefore, the growth of two hybrid families, Populus deltoides 'S9-2' x Populus nigra 'Ghoy' (D x N family, 180 F(1)) and P. deltoides 'S9-2' x Populus trichocarpa 'V24' (D x T family, 182 F(1)), was investigated during a 3-year period at two sites, i.e., in northern Italy and central France. At the end of the second growing season, all trees were coppiced and the resprouts were thinned to a single stem. At the end of each growing season, stem circumference and height were measured for all F(1) hybrids. The number of sylleptic branches, individual leaf area (LA) and petiole length of the largest leaf along the main stem, production of new leaves, bud flush and bud set were estimated for a selection of genotypes (31 F(1)) per family at each site during the course of the 3-year experiment. The D x T family was clearly the most productive family and displayed the highest heterosis values. However, there appeared to be a compromise between good growth at a given site and stability between the two different sites, both at family and at genotype levels. Particularly, the less performing trees were stable between Italy and France. Among the studied growth components, the number of sylleptic branches and individual LA of the largest leaf along the main stem were the best growth predictors, irrespective of site and family. Growth strategies in terms of leaf development differed between the two families. Hence, leaf production rate was strongly associated with growth of the D x N family only. These results have important consequences for the use of the studied traits as selection criteria in breeding programmes.
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ABSTRACT: The implications of extensive variation in leaf size for biomass distribution between physiological and support tissues and for overall leaf physiological activity are poorly understood. Here, we tested the hypotheses that increases in leaf size result in enhanced whole-plant support investments, especially in compound-leaved species, and that accumulation of support tissues reduces average leaf nitrogen (N) content per unit dry mass (N(M)), a proxy for photosynthetic capacity. Leaf biomass partitioning among the lamina, mid-rib and petiole, and whole-plant investments in leaf support (within-leaf and stem) were studied in 33 simple-leaved and 11 compound-leaved species. Support investments in mid-ribs and petioles increased with leaf size similarly in simple leaves and leaflets of compound leaves, but the overall support mass fraction within leaves was larger in compound-leaved species as a result of prominent rachises. Within-leaf and within-plant support mass investments were negatively correlated. Therefore, the total plant support fraction was independent of leaf size and lamina dissection. Because of the lower N(M) of support biomass, the difference in N(M) between the entire leaf and the photosynthetic lamina increased with leaf size. We conclude that whole-plant support costs are weakly size-dependent, but accumulation of support structures within the leaf decreases whole-leaf average N(M), potentially reducing the integrated photosynthetic activity of larger leaves.New Phytologist 02/2006; 171(1):91-104. · 6.74 Impact Factor
Article: Heterosis: revisiting the magic.[show abstract] [hide abstract]
ABSTRACT: Heterosis results in the phenotypic superiority of a hybrid over its parents with respect to traits such as growth rate, reproductive success and yield. This hybrid vigor is determined by non-mutually exclusive mechanisms, including dominance complementation, overdominance and epistasis. Heterotic genes responsible for elevating crop yields are now being sought using genomics, particularly transcriptomics, but with contradictory results. Because heterosis is an environmentally modified quantitative phenotype, genomic analyses alone will not suffice. Future research should focus on integrating genomic tools in a framework of comprehensive quantitative trait locus (QTL)-based phenotyping, followed by map-based cloning. This 'phenomics' approach should identify loci controlling heterotic phenotypes, and improve understanding of the role of heterosis in evolution and the domestication of crop plants.Trends in Genetics 03/2007; 23(2):60-6. · 9.77 Impact Factor
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ABSTRACT: Although Populus has become the model genus for molecular genetics and genomics research on forest trees, genetic and phylogenetic relationships within this genus have not yet been comprehensively studied at the molecular level. By using 151 AFLP (AFLP is a registered trademark of Keygene) markers, 178 accessions belonging to 25 poplar species and three interspecific hybrids were analyzed, using three accessions belonging to two willow species as outgroups. The genetic and phylogenetic relationships were generally consistent with the known taxonomy, although notable exceptions were observed. A dendrogram as well as a single most parsimonious tree, ordered the Populus sections from the oldest Leuce to the latest Aigeiros, a pattern consistent with their known evolutionary relationships. A close relationship between Populus deltoides of the Aigeiros section and species of the Tacamahaca section was observed and, with the exception of Populus wilsonii, between the species of the Leucoides, Tacamahaca, and Aigeiros sections. Populus nigra was clearly separated from its consectional P. deltoides, and should be classified separately from P. deltoides. The AFLP profiles pointed out to the lack of divergence between some species and revealed that some accessions corresponded with interspecific hybrids. This molecular study provides useful information about genetic relationships among several Populus species and, together with morphological descriptions and crossability, it may help review and update systematic classification within the Populus genus.Theoretical and Applied Genetics 12/2005; 111(7):1440-56. · 3.66 Impact Factor