Effect of six rootstocks on 'Forelle' pear tree growth, production, fruit quality and leaf mineral content
Commercially produced European pear cultivars in South Africa are grown predominantly on the common pear (Pyrus communis L.) and less on quince (Cydonia oblonga L.) rootstocks, possibly because of the marginal soil conditions and limited water supply during the growing season in the traditional fruit growing regions of the Western Cape Province. While the former rootstock tends to promote more vigour in the scion, quince rootstocks propagate more easily, but graft incompatibility may be a problem. Diverse soil, environmental and management conditions have necessitated an extensive pear rootstock evaluation process. The adoption of higher density orchards, especially under fertigation and drip irrigation necessitated a re-evaluation of commercially available rootstocks (BP3, BP1, OH×F97, BA29, QA & QC51) using the popular commercial blushed pear 'Forelle'. Data is presented over five seasons from trees planted at 4.2×0.5×0.5 m and trained to a modified Tatura trellis. Rootstock had a significant effect on stem diameter, tree height and number of growth points. Stem diameter was the only parameter directly correlated with yield and there were no differences in cropping efficiency. Rootstock influenced fruit background colour but not size, blush, firmness or TSS during the first harvest and influenced fruit size, background colour and blush, but not fruit firmness or TSS during the second. The largest fruit size occurred on the more dwarfed trees, although harvested fruit number generally did not differ. 'Forelle' after 5 seasons were excessively vigorous on BP3 while trees on BP1 and BA29 had filled their allocated space. However, trees on OH×F97, QA and QC51 could have been planted closer. Trees on pear rootstocks had higher levels of N and P and lower Mg levels than trees on quince which may influence storage ability.