South African Avocado Growers’ Association Yearbook 1998. 21:13-18 Performance of Rootstock Cultivars in the Avocado Phase II Evaluation Programme: 1997 A.D. Sippel, C.W. Matsha & Z. Bijzet ARC-lnstitute for Tropical and Subtropical Crops, Private Bag X11208, Nelspruit, 1200 ABSTRACT The purpose of a rootstock evaluation trial is to collect information on the performance of important avocado cultivars in combination with various rootstock cultivars. The first ARC-ITSC trials were established with five rootstock cultivars, namely Duke 7, Thomas, G6 combination with the commercial scions Fuerte, Hass, Pinkerton and Ryan. These trials were planted at Levubu and Bürgerst however, lost during 1996 as a result of the excessive rains of that season. With Fuerte the best yield per tree came from scions grafted on the Thomas rootstock, at 40.6 kg fruit per tree. This rootstock was also the best performer based on tree size. Hass also had the best per tree yield also on Thomas, but based on tree size, performed better on Duke 7. Pinkerton produced an average of 64.5 kg fruit/tree on Duke 7, with this rootstock also being the best on a tree volume basis. Ryan production was very poor with G6 being the better rootstock at 16.2 kg fruit/tree. However, based on tree volume the best combination (Ryan on Thomas) outperformed the best Fuerte combination. Data from only the first three years of production are presented. It is suggested that data from two years more should be added before any specific recommendations can be made from this trial. UITTREKSEL Die doel van 'n onderstam evaluasie projek is om inligting te versamel aangaande die prestasie van belangrike avokado bostamme in kombinasie met verskeie onderstam kultivars. Die eerste LNR-ITSG proewe is geplant met vyf onderstam kultivars, naamlik Duke 7, Thomas, G6, Duke 9 en G755, in kombinasie met die komrnersieele bostamme Fuerte, Hass, Pinkerton en Ryan. Hierdie proewe is geplant by beide Levubu en Burgershall. Laasgenoemde perseel se proef moes egter gestaak word aangesien die borne doodgegaan net as gevolg van die oormatige reens gedurende die 1995/96 seisoen. Met Fuerte as bostam en Thomas as onderstam is die beste opbrengs per boom, naamlik 40.6 kg vrugte, verkry. Hierdie onderstam was ook die beste presteerder gebaseer op boom grootte, of te wel, kilogram vrugte per volume eenheid. Waar Hass die bostam was, was die beste opbrengs op 'n per-boom-basis ook verkry met Thomas as onderstam, maar gebaseer op volume het die Duke 7 onderstam beter presteer.