Breeding, Genomics, and Selection of Shrub Willow Bioenergy Crops for Yield and Biomass Composition.

Shrub willow (Salix spp.) is a proven, high-yielding perennial woody crop that is well suited for cultivation on underutilized or marginal agricultural land in the Northeast and Midwest US and in parts of Canada, especially on land not used for food crops.  With only a short history of willow breeding, there is tremendous potential to improve the yield, biomass composition, and site adaptability of Salix through breeding, selection, and hybridization.  A willow breeding program was established in New York in the late 1990’s that has to date produced over 7000 progeny in ~300 families.  New varieties, including some novel species hybrids, have been selected based on increases in yield as high as 40% in initial trials and are currently being tested across a range of sites in North America and in a few locations in Europe.  Plant patents have been issued in the US for seven of these, stimulating commercialization through licensing to a commercial willow nursery, Double A Willow in Fredonia, NY. Using wet chemical analysis and high-resolution thermogravimetric analysis, we have characterized significant variation in biomass composition among genotypes of shrub willow produced through breeding.  To gain an understanding of the molecular basis for differences in biomass composition, we have correlated the patterns of expression of genes encoding enzymes involved in lignin, cellulose, and hemicellulose biosynthesis with variation in biomass composition among several genotypes.  Expression profiling in willow stem apical tissue and developing stem tissue was performed for each isolated gene using probe-based quantitative real-time PCR.  Currently, the sequencing of the Salix purpurea genome is in the queue at the DOE Joint Genome Institute, which will allow for comparative genomics with poplar for key biomass traits and encourage future selection strategies using genomics-based marker-assisted selection.