Diverse growth and sylleptic branching patterns in Japanese maple cultivars

Branching is a key determinant of architectural quality of ornamental plants. Using plants trained to a single primary shoot, cultivars of Japanese maple (Acer sp.) 'Fireglow, 'Katsura, 'Orangeola, 'Red Emperor; 'Skeeter's Broom' and 'Sango Kaku' presented a diverse range of growth and sylleptic branching patterns. Shoot extension was more vigorous in 'Sango Kaku, which displayed uninterrupted extension to develop more than 30 metamers. In other cultivars, some primary shoots had a pause after extension of approximately six preformed metamers, forming shorter bicyclic shoots (e.g., 'Red Emperor'); and some of the shoots were monocyclic, comprising mostly preformed metamers (e.g., 'Fireglow'). Sylleptic branching in the six cultivars differed in both branching intensity and the location of branches along the primary shoot. 'Sango Kaku' and 'Katsura' featured two intensely branched zones with lower branching frequency between them. 'Orangeola' and 'Skeeter's Broom' had a single branching zone with lower branching intensity located at the basal and middle sections of the parent shoot, respectively. In addition, xylem sap of 'Red Emperor' contained more strigolactone than that of 'Sango Kaku, supporting the hypothesis that sylleptic branching appears to correlate inversely with the amount of strigolactone. The above results support the hypothesis that the occurrence of sylleptic branching and these branches' distribution along the primary shoot are subject to combined hormonal and developmental control. Possible relationships between the primary shoot organogenesis/extension and the time course of sylleptic branching are currently being investigated.