Environmental and genetic influences on growth characteristics in a full sib family of Populus nigra
Author(s)
Ludovisi, Riccardo
Date Issued
June 24, 2014
Type
Doctoral Thesis
Abstract
Growth related traits in trees are fundamental components of survival and productivity in natural and planted forests. This wide category of traits refers to many attributes, such as aboveground biomass production and spring bud phenology. Wood trees provide a sustainable source of carbon-neutral bioenergy, and plant phenology represents a serious ecological and evolutionary trade-off between survival and growth. Aboveground biomass production and allocation are the result by interaction among climate condition, genetics variance and silvicultural management. Phenology is responsive to global warming, especially spring bud flush that is predominantly controlled by temperature. The aim of this study was to improve the knowledge of genetic basis and environmental influence related to: (i) biometric traits and biomass production; (ii) bud flush dynamics focusing on the influence of temperature on this process. A Populus nigra full-sib family (POP5) originating from a controlled cross between parental genotypes from contrasting climate was studied at different locations and in different growing seasons. Different linear regression models, based on biometric traits, were developed to estimate biomass yield for each environment. Model accuracy was very high and has been possible to standardize estimation models between growing seasons in the same location. High phenotypic variance was observed in the trials, in particular among plantations with different age root system. Northern parent “58-861” shown greater adaptability and productivity (11.6 t ha-1 year-1) compared to the southern parent “Poli” (3.4 t ha-1 year-1). Mean POP5 productivity was 11.3 t ha-1 year-1. Very low values of heritability (H2<0.25) were observed for the different biometric and biomass traits in the trials. The relative importance of environment, genotype and genotype × environment (G×E) interaction effects on total phenotypic variation of growth traits was estimated. Significant G×E interaction was observed for sites characterized by lack of coppicing at the end of first growing season. A large number of QTLs, 41 on paternal map and 44 on maternal map were found, corresponding to 11 and 8 genomic regions, respectively. QTLs were characterized by small or modest effect (average PVE=6%). Four common molecular markers (ORPM_127, PMGC_2839, PMGC_2423, PMGC_520) were found between maternal and paternal maps on four different linkage groups (LG IV, V, VI, XV). On LG XIX, five QTLs were found for height using multi-environment analyses. A protocol was developed for black poplar (P. nigra) to dissect the bud burst spring phenology in different stages, from the swelling of the buds to the complete leaf formation, passing through three intermediate phases. Cumulative average temperature above 10°C (CAT10) and cumulative minimum temperature below 5°C (CMT5) were used to describe phenotypic and genetic variance of the bud flush stages. Two growing seasons were compared in the site of Viterbo. Both growing seasons showed similar CAT10 values for the initial stage of bud flush, despite seven days of difference for the bud flush initiation observed between the years. Southern parent was more sensible to temperature variation than the northern parent. Greater fluctuations in temperatures increased the extent of phenotypic variance among genotypes during the process than stable temperatures. Moderate to low values of heritability (H2<0.50) were observed for the different stages in the two years. No significant G×E interaction was observed. A large number of QTLs, 28 on paternal map and 26 on maternal map, were found, corresponding to 9 genomic regions for each parent. QTLs were characterized by small or modest effect (average PVE=6.7%), without common genomic regions between parental maps. These results highlight the complex nature of the traits involved in woody biomass determination and during bud flush and leaf elongation process.
Additional information
Dottorato di ricerca in Ecologia forestale
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