Relation between nitrogen status carbohydrate distribution and subsequent rooting of chrysanthemum cuttings as affected by pre-harvest nitrogen supply and cold-storage

Abstract

This study investigated the relationship between internal nitrogen and carbohydrate distribution in chrysanthemum cuttings of two cultivars ('Puma', 'Cassa') when affected by nitrogen supply to stock plants (0.6, 1-5, or 4.0 g N m-2 week-1) and different periods (2, 3, or 4 weeks) of dark cold-storage (0.5 or 5°C), and adventitious rooting. Concentrations of total nitrogen (N(t)) and nitrate in cuttings and the levels of sugars, starch and fructan in different cutting parts (leaves, upper stem, and basal stem) were studied in relation to subsequent adventitious rooting at natural radiation in a greenhouse. Increasing nitrogen supply resulted in substantially lower starch levels and higher sucrose concentrations in leaves when cuttings were excised. Fructan concentrations were low and decreased with increasing nitrogen levels. Starch completely disappeared from leaves and to a large extent from stems within the shortest storage period. A less pronounced decrease in sugar concentration was observed, particularly in low-nitrogen cuttings and the cuttings of 'Puma'. The number and length of adventitious roots subsequently formed by unstored and stored cuttings was positively correlated with initial N(t), and to a lesser extent with initial nitrate concentrations in cuttings. Whereas rooting was not limited by pre-rooting concentrations of carbohydrates in the different cutting parts, the generally higher rooting capability of nitrogen-rich cuttings, a stronger nitrogen response of 'Cassa', and increased rooting at a particular harvest date, were associated with higher sucrose:starch ratios in leaves at harvest. This reflected an increased assimilate export. By using this characteristic in a linear regression model, total variability of root numbers, ranging from three-35 per cutting, could be predicted to 57% for the unstored and to 40% for all cuttings. Increased basipetal transport of carbohydrates, of nitrogen compounds, and of auxins may be causally involved in these associations. (C) Annals of Botany Company.