A Strategy for the Second Breeding Cycle of Larix x marschlinsii in Québec, Canada Including Experiments to Guide Interspecific Tree Breeding Programme

A strategy for the genetic improvement of Larix decidua P. Mill., L. kaempferi (Lamb.) Carrière and their hybrid (L. x marschlinsii Coaz) in Québec, Canada, was set up to provide short and long-term genetic gains, as well as basic populations for some fundamental experiments. A reciprocal recurrent selection with forward selection strategy (RRS-FS) will be applied by using a pollen mix breeding with a partial population paternity analysis (PMX/WPPA). The genetic mechanisms responsible for heterosis among trees remain poorly understood. This complicates the implementation of multi-species genetic improvement programmes seeking to achieve the full benefits of interspecific hybridization. Various strategies to exploit heterosis are outlined. To expand our knowledge and guide our future choices, basic research has been integrated directly into breeding and testing activities, as well as through experiments integrated within activities leading to recommendations about the top-ranked families to be used in reforestation (cuttings). These experiments can also serve as the basis for future studies seeking a better understanding of heterosis through molecular genetics.