Genotype x Environment Interactions in First-Rotation Yields of Improved Shrub Willow Cultivars in North America.

Shrub willow has shown promise as a viable regionally-based feedstock for sustainable bioenergy production on marginal land, due to its large potential for improvement through breeding and relatively high yields in cool, moist climates with short growing seasons. Despite substantial gains in potential yield through breeding efforts, actual yields are unpredictable due to a lack of understanding of how willow interacts with the environment. Exploring these genotype by environment interactions will help to identify cultivars with stable yields and adaptability to local conditions. It will also help to isolate the site variables that most impact yield. We present the most comprehensive analysis to date of shrub willow yields from North America. We applied the additive main effects and multiplicative interactions (AMMI) model to a shrub willow yield trial network dataset containing first rotation yields of 22 cultivars in 16 environments. The ANOVA indicated significant main effects of genotype and environment, as well as their interaction. The IPC analysis showed that the first axis accounted for 69% of the interaction pattern sums of squares, and was two thirds as important as the genotype main effect. The AMMI1 model explained 93% of the treament sums of squares. The two winning cultivars identified by the AMMI1 mega-environment analysis were both triploid hybrids, specifically of a Salix viminalis x S. miyabeana pedigree. The environmental factors that were most closely associated with the IPC1 scores were temperature and growing degree days. The first rotation yield data from this network of trials will provide valuable information for cultivar-site matching recommendations and for future breeding efforts.