Tolerance of novel inter-specific shrub willow hybrids to water stress

Abstract

KEY MESSAGE: Novel interspecific hybrid progeny displayed hybrid vigor for some key biomass traits under well-watered and water-stressed conditions, but response was genotype-specific. Adaptation to stresses caused by climate change resulting from greenhouse gas emissions will become increasingly important for perennial crop breeding programs in the coming decades. Shrub willow (Salix spp.) is a strong candidate for short rotation coppice bioenergy production due to its high biomass production capacity, especially in temperate, northern latitudes. However, climate change is expected to increase temperature and the unpredictability of growing-season precipitation in these regions. Previous research has shown that interspecific breeding of shrub willow has resulted in hybrid vigor for biomass production. It is unclear how novel hybrids will perform in water limiting conditions. Using a biparental breeding scheme with common S. purpurea male or female parents, we tested parents and progeny for changes in growth and physiological traits under well-watered conditions and two levels of water stress. Water stress treatments caused reductions in above- and belowground biomass, leaf traits and stomatal conductance, mainly at the severe treatment level. At the genotypic level, hybrid progeny generally outperformed their parents for growth and biomass traits, demonstrating heterosis in these interspecific crosses. We found evidence that genotypes with the highest rates of biomass production are most severely impacted by water stress. Foliar SPAD measurements, a proxy for foliar N, were unaffected by water stress treatments. Biomass among genotypes in this controlled environment experiment was significantly correlated with field-grown plants, validating that these results can help to inform future breeding efforts targeting improved crop performance in drier growing environments.