The aim of this study was to examine the genetic control of time-to-flowering (precocity) in 39 open-pollinated families of Eucalyptus cladocalyx in southern Atacama Desert, Chile, with the view to the selection of trees that flower earlier but with minimal impact on survival and growth. A Bayesian approach, implemented using Gibbs sampling algorithm, was used in data analyses. Precocity was assessed as a binary response at age three and was found to be highly heritable. The estimates of posterior mean and of the 95% posterior interval of the heritability were 0.51 and [0.46-0.56], respectively. Estimated genetic gain ranged from 36.15 to 41.22% (selection intensities of 14.29 and 7.48%, respectively). Total height, basal diameter and survival (measured at age 5) had a positive and relatively moderate genetic correlation with early flowering (r = 0.23, 0.29 and 0.11, respectively) indicating that selection for early flowering alone would have a moderate impact on growth and survival. Early flowering of Eucalyptus cladocalyx was found to be highly heritable in southern Atacama Desert populations, which could be used to improve the honey production in situations where flowers from native species are not available in sufficient quantities.

Abstract

In the dry regions of Chile, prolific flowering from forest plantation is particularly advantageous for honey production, in order to supplement the erratic flowering in native plants. Eucalyptus cladocalyx is a species suitable for areas with low water availability and their flowers provide a reliable source for the production of honey. The aim of this study was to examine the heritability of flowering intensity in 49 open-pollinated families of E. cladocalyx in southern Atacama Desert, Chile, with the view to the selection for prolific flowering, but with minimal impact on precocious flowering. The Bayesian variance component estimation model was assumed using the Gibbs sampling algorithm. Threshold models were fitted to flowering data (bi-character model). Flowering intensity was found to be highly heritable (posterior mean: h 2 = 0.48; and credible interval: 0.41-0.56). The posterior mean of the genetic correlation between flowering precocity and intensity was positive (r = 0.45) and according to the credible interval (0.341-0.542), it was significantly different from zero, indicating that selection on breeding values of early flowering at age three, would have significant and positive impact on flowering intensity 5 years later (or in 8-year-old trees). These results are important for the start of a small-scale breeding program for the species in southern Atacama Desert. The genetic variability found in these breeding populations may be used for breeding purposes in regions where arid environmental conditions are limiting to the establishment of eucalypts trees.

ABSTRACT. Eucalyptus cladocalyx F. Muell is a tree endemic to southern Australia and is distributed across four isolated regions: Kangaroo Island, southern Flinders Ranges, and two geographical zones in Eyre Peninsula. E. cladocalyx is capable of growing under extreme environmental conditions, including dry and saline soils. The objective of this study was to analyze genetic diversity in 45 half-sib families planted in northern Chile that are distributed across five different zones (provenances). Genetic variability was assessed using ISSR (Inter Simple Sequence Repeat) molecular markers. The results showed low levels of genetic diversity within populations (He = 0.113 to 0.268) in contrast with other Eucalyptus species. In addition, there was a significant genetic differentiation among provenances (Φst = 0.14); populations from the Kangaroo Island provenance showed more differentiation than any other population. These results are in agreement with previous studies of the species. Our study revealed that Chilean resources are a representative sample of Australian populations; therefore, the germplasm planted in northern Chile would be sufficient for the development of improvement programs. ISSR-Marker technology could be an alternative to identify genotypes of interest in material selection.

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