Ad hoc breeding and occasional disorders – a case study on current season needle necrosis in Nordmann fir (Abies nordmanniana (Steven) Spach)

Abstract Ad hoc breeding of forest trees, noted for its flexibility, has been predicted to be useful for addressing pests, diseases, and disorders under specific conditions. This study aimed to demonstrate the use of ad hoc breeding to address the occasional disorder current season needle necrosis (CSNN) in Nordmann fir. First, 1545 random reference trees from two plantation stands in Denmark (689 from Tørring and 856 from Mariager) with a known parental population (clonal seed orchard FP.266 Skibelund) were used. Second, to specifically screen for CSNN, 495 moderately to severely damaged trees (Sel-495) were selected from the most affected area in the Mariager stand. Clonal parents from FP.266 were ranked based on either the prevalence of CSNN in their offspring (Sel-495) or their breeding value following SNP-based parentage and quantitative genetic analysis (reference trees). In the Sel-495 dataset, 55.6% of the affected offspring originated from 20% of the parents, while 36% of the clonal parents had moderately or severely affected offspring in the reference trees. Moderate overlap was observed between clonal parents’ ranking based on breeding values and the ranking based on the over-frequency of their offspring in Sel-495 trees. Overall, ad hoc breeding and parentage analysis facilitated backward selection against CSNN by enabling the estimation of genetic parameters ( h 2 = 0.08 ± 0.04) using reference trees and identifying high-risk parents. A combination of breeding value rankings and ranking based on CSNN prevalence in their offspring was used as a parental selection approach. The findings demonstrate that ad hoc breeding is an effective, flexible strategy for managing and breeding against unpredictable disorders in forest trees under changing climate conditions.