Vol. 71 No: 4

Title:
Relationships Between Shoot Growth and Rooting of Cuttings in Three Contrasting Species of Ornamental Shrub

Author:
B.H. HOWARD

pp: 591-606

Abstract:
Apical cuttings of the difficult-to-root Syringa vulgaris ‘Madame Lemoine’ rooted well only during a brief period of rapid shoot growth in early summer, and even then only when the stockplants had been severely pruned in the previous late winter. Rooting was poor early in the period of shoot growth and, after reaching a peak in early June, declined as shoot growth stopped. The relatively difficult-to-root Cotinus coggygria ‘Royal Purple’ behaved somewhat similarly to Syringa, with rooting being confined to the period of active shoot growth, which was longer than for Syringa, and with a smaller benefit from severe stockplant pruning. Forsythia × intermedia ‘Lynwood’ rooted well throughout the summer regardless of shoot growth rate and earlier pruning severity. In Syringa, the opportunity to enhance rooting, especially in cuttings from the less severely pruned source, by growing shoots temporarily in the dark, was limited to the period of active shoot growth. Producing a late flush of rapidly growing shoots after earlier cutting collection, or delaying shoot growth by holding back potted stockplants in cold store, created ready-rooting cuttings at a normally non-rooting time. Seasonal rooting trends, although not actual rooting levels, were generally similar in a polythene house environment changing naturally with weather and season, and in a constant controlled environment. Because rooting correlated so strongly with active stockplant growth at the time of cutting collection, the implication is that some condition of the growing shoot determines rooting. However, the shoot apex was not implicated directly during the two weeks before or during rooting for Syringa and Cotinus, and all Forsythia cuttings rooted despite treatment combinations involving the removal of the shoot apex. In practice, close attention to matching propagation time, treatments and environments with optimal shoot growth will achieve success in species least genetically disposed to root, and provides a sharp focus for investigating the rooting mechanism via physiological, biochemical and molecular approaches.

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