Phenotyping vigour control capacity of new peach rootstocks by xylem vessel analysis

In peach, xylem anatomical characteristics have been shown to be related to vigour of selected rootstocks. The goal of this research was to determine if xylem characteristics of a new set of rootstocks that exhibit a range of size-controlling potential and have a different genetic background from previously examined material would also exhibit similar differences in xylem characteristics. If so, then anatomical analysis of xylem may be a useful means of predicting the vigour control capacity of selected peach rootstock genotypes. Samples of xylem tissue were taken from roots, trunks and shoots of four new rootstocks that were derived from a genetic cross between ‘Harrow Blood’ and ‘Okinawa’ peaches and compared with tissue from ‘Nemaguard’, a vigorous control. Xylem samples were sectioned and analysed by optical microscope. The number and dimensions of vessels in recently developed xylem of each rootstock were measured and compared. The more dwarfing rootstocks had fewer large vessels and more small vessels than the more vigorous rootstocks. Weighted mean vessel diameter (Wm) and calculated hydraulic conductance (Kh) differed among rootstocks: more vigorous rootstocks had higher Kh and Wm than dwarfing rootstocks. Rootstock xylem vessel dimensions varied in relation to the vigour they imparted to a common scion cultivar (‘O’Henry’). After the ‘Nemaguard’ control, ‘HBOK 50’ was the most vigorous rootstock followed by ‘HBOK 10’, ‘HBOK 32’ and ‘HBOK 27’, respectively. Thus, as was seen in previous research with a separate set of rootstocks, the vigour-control capacity of this new series of peach rootstocks was strongly related to their xylem hydraulic characteristics and it appears likely that it would be possible to use xylem anatomical characteristics of shoots or roots of young trees to pre-select for size-controlling potential in a rootstock development program.

Research highlights▶ This paper follows a series of previous papers concerning the physiological basis for the size-controlling capacity of a series of peach rootstocks. The previous studies documented that the size-controlling behaviour was linked to diurnal patterns of stem water potential and that those patterns were linked to rootstock hydraulic conductance. Subsequently we showed that there are clear relationships between the previously measured differences in rootstock hydraulic conductance among rootstocks and both xylem anatomy and theoretically calculated hydraulic conductance of the same rootstocks. ▶ In addition to confirming previous findings about the relationships between xylem anatomy and tree vigour on a new set of peach rootstocks this paper shows that it may be possible to characterize the potential vigour controlling behaviour of some peach rootstocks by simply studying their xylem anatomy.