Growth performance of hybrid poplar clones on two agricultural sites with and without early irrigation and fertilization

Growth, clone rank, genotype x environment interaction, and effects of early fertilization and irrigation were evaluated for 56 hybrid poplar clones after three years’ growth on two agricultural sites in Indiana, USA. Forty-eight percent of the clones were Populus deltoides x P. nigra (DxN) crosses made with a female parent of Minnesota provenance, with the hybrids or female parent screened in Minnesota for survival, growth rate, and disease tolerance or resistance. Forty-one percent of the clones had at least one parent from provenances that are more southerly and/or have more moderate climates of provenance origin than Minnesota. Eleven percent of the clones were screened in Minnesota but were either not DXN crosses or did not have parents from Minnesota provenances in their parentage. Height growth averaged 1.78 m per year for all clones over all treatments and 2.02 m per year for the fastest- growing six clones (top 10^th percentile). Tree bole volume for the fastest-growing 10 % of the clones was 70 % larger than the average of two commercial standard clones. The clonal effect was dominant in comparison to site, treatment, and interaction effects. The fertilizer, irrigation, and fertilizer x irrigation treatments tended to increase growth, but the statistical significance of the treatment effects differed by site, and the treatments explained only a small portion of the variance. Clone rank was the same on both sites, regardless of treatment, except for the fertilizer x irrigation treatment. DxN clones linked to Minnesota parentage out-performed most clones of more southerly or other more moderate climatic origins, in these tests conducted far south of Minnesota. The data provide further evidence of broad adaptability of DxN hybrids with female P. deltoides parents of Minnesota provenance, possibly eliminating the need for narrow breeding zones and reducing the number of screening tests needed at different latitudes, saving time and money. Tests are planned to further analyze and possibly extend this inference.