Gibberellins and heterosis in poplar

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Abstract
To investigate the possible involvement of gibberellins (GAs) in heterosis of hybrid poplar, six poplar clones were studied, including two Populus deltoides clones and two interspecific hybrid clones (P. ×euramericana = P. deltoides × P. nigra) originating from crosses with each of the P. deltoides clones. In field conditions in Ontario, Canada, the interspecific hybrids were consistently taller and had greater shoot dry weights than their parental P. deltoides clones. Shoot dry weights and heights were highly correlated across the six clones, as clonal rankings for these parameters were identical. Endogenous GA-like substances were extracted, purified, chromatographed on silica gel partition columns, and quantified by the cv. Tan-ginbozu dwarf rice bioassay. Bioactive peaks were further chromatographed on reversed-phase C18 HPLC and again bio-assayed. Statistically significant differences in concentrations of total GA-like substances were observed. With one exception, the rankings for the concentrations of GA-like substances and those of GA1-like plus GA19-like substances were similar to the rankings for height growth. Gibberellins A1 and A19 have been identified from the tissue of hybrid poplar by capillary gas chromatography – selected ion monitoring (GC–SIM), and GA1 was also identified by GC–SIM in this tissue. In three of four comparisons, interspecific hybrids contained significantly higher concentrations of GA-like activity than their corresponding parental clones. Thus, a correlation was observed between the concentration of endogenous GA-like activity and hybrid vigor for height growth and shoot dry weight in poplar.