Field performance of progenies of Pinus radiata selected for resistance to Diplodia-associated shoot dieback

Abstract

Background: A severe outbreak of Diplodia-associated dieback of Pinus radiata D.Don shoots in 1967 prompted a pilot programme of selection for resistance to dieback. Plus trees were selected in 1970 for absence of dieback, growth and tree form, and seed collected. Methods: Twenty open-pollinated progenies plus two control lots were field-tested on two sites, and assessed around 6.5 years after planting. Alternative measures of shoot dieback were recorded, as were dbhob and scores for growth and form variables. Data were analysed for seedlot differences, heritability estimates and various genetic correlations. Results: Dieback at one site allowed good resolution of progeny differences, whatever the dieback measure. Remarkably, no response to field selection for resistance was evident, unlike in a glasshouse inoculation trial. Nor did progeny rankings correlate with those in the inoculation trial. Between the trial sites no clear seedlot rank changes were evident for any trait. Conclusions: The disparity with results from the inoculation trial is unexplained, although a role of endophyte status is postulated. Together with non-recurrence of past dieback outbreaks, the disparity means that selection for field resistance is not promising.