Quantitative Genetic Variation in Bark Stripping of Pinus radiata

Abstract

Bark stripping by mammals is a major problem for conifer forestry worldwide. In Australia, bark stripping in the exotic plantations of Pinus radiata is mainly caused by native marsupials. As a sustainable management option, we explored the extent to which natural variation in the susceptibility of P. radiata is under genetic control and is thus amenable to genetic improvement. Bark stripping was assessed at ages four and five years in two sister trials comprising 101 and 138 open-pollinated half-sib families. A third younger trial comprising 74 full-sib control-pollinated families was assessed at two and three years after planting. Significant additive genetic variation in bark stripping was demonstrated in all trials, with narrow-sense heritability estimates between 0.06 and 0.14. Within sites, the amount of additive genetic variation detected increased with the level of bark stripping. When strongly expressed across the two sister trials, the genetic signal was stable (i.e., there was little genotype × environment interaction). No significant non-additive effect (specific combining ability effect) on bark stripping was detected in the full-sib family trial, where it was estimated that up to 22.1% reduction in bark stripping might be achieved by selecting 20% of the less susceptible families. Physical traits that were genetically correlated, and likely influenced the amount of bark removed from the trees by the marsupials, appeared to depend upon tree age. In the older trials, these traits included bark features (presence of rough bark, rough bark height, and bark thickness), whereas in the younger trial where rough bark was not developed, it was the presence of obstructive branches or needles on the stem. In the younger trial, a positive genetic correlation between prior height and bark stripping was detected, suggesting that initially faster growing trees exhibit more bark stripping than slower growing trees but later develop rough bark faster and became less susceptible. While the presence of unexplained genetic variation after accounting for these physical factors suggests that other explanatory plant traits may be involved, such as chemical traits, overall the results indicate that selection for reduced susceptibility is possible, with potential genetic gains for deployment and breeding.

Developing near infrared spectroscopy models for predicting chemistry and responses to stress in Pinus radiata (D. Don)

“…On the same populations large changes were detected in primary and secondary compounds after treatment, with differences in time progression of the compounds in the different plant parts. 13 The strongest quantitative changes were detected 14 and 21 days after treatment application. In other P. radiata populations, Reglinski et al.…”

“…33 Some samples were extracted in triplicates for estimation of laboratory error. The amounts of compounds quantified in the different plant parts were presented elsewhere 13 and these include terpenes, phenolics, sugars, fatty acids and compounds that were not classified into the four classes (unknown compounds). All compounds were given an identifier for ease of location in the tables.…”

“…in plant roots) may also influence herbivory patterns. 12,13 Common methods used to characterize the chemical resistance traits include thin layer chromatography, high-performance liquid chromatography, gas chromatography, liquid chromatography–mass spectrometry and gas chromatography–mass spectrometry. 14,15 Most of these methods are time-consuming, labour-intensive and expensive.…”

“…Susceptibility may be determined by both constitutive and induced physical and chemical defence traits. 13 In Pinus radiata , the constitutive and induced chemistry, following methyl jasmonate or artificial wounding, has been characterised in the needles, bark 3,25 and roots 13 using conventional wet chemistry techniques, as well as the physical traits. 26 Except for Moreira et al.…”

“…13 In Pinus radiata , the constitutive and induced chemistry, following methyl jasmonate or artificial wounding, has been characterised in the needles, bark 3,25 and roots 13 using conventional wet chemistry techniques, as well as the physical traits. 26 Except for Moreira et al. 3 who demonstrated genetic control for total compounds, the genetic control of individual traits has not been documented.…”