Hormonal relationships in xylem sap of grafted and ungrafted Prunus rootstocks

Three Prunus species, characterised by different levels of growth vigour, were used as rootstocks for peach [Prunus persica (L.) Batsch] grafting and compared for their hormone transport rates in the sap extracted from both the grafted scions and the ungrafted rootstocks. Two of these species were hybrid rootstocks widely used in peach orchards, while the third was a commercial cultivar, which was used both as rootstock and as scion. The xylem exudates were analysed for the concentrations of indoleacetic acid and for the main cytokinins, namely zeatin, zeatin riboside, isopentenyl-adenine and isopentenyl-adenosine. In ungrafted rootstocks the growth potential was positively correlated with both indoleacetic acid and zeatin riboside transport rates. In the xylem sap of peach scions grafted on the same rootstocks, the growth potential and the zeatin riboside levels were also positively correlated, while a negative correlation was found with indoleacetic acid levels. The results are discussed in view of the most widely accepted hypothesis concerning the control exerted by rootstocks on scion growth. (C) 2002 Elsevier Science B.V. All rights reserved.