Article topic: AVOCADO ROOTSTOCK RESEARCH: PRINCIPLES AND PRACTISES
Author(s): A.I. de Villiers, A.A. Ernst
Abstract
The value of a reliable clonal rooting technique has been reported. A direct correlation between the quality of a rooting system and tree uniformity has been illustrated. Clonally propagated rootstocks are the only way to express certain outstanding tree characteristics of the scion, such as precocity and production. However, seedling rootstocks are predominantly still used in many countries as the preferred rootstock. The effect of temperature and growth medium to improve root quality and quantity as well as the influence of different rootstocks on the field performance of ‘Hass’ and ‘Maluma’, has been studied. Using the Allesbeste micro cloning technique with coco peat as growth medium and a rooting temperature of between 20 – 28°C ensures superior clonal root development. With ‘Hass’ as the fruiting cultivar, ‘Duke 7’ outperformed ‘Duke 7’seedling rootstocks on production and uniformity, while on production ‘Duke 7’, ‘D9’ and ‘BarrDuke’ outperformed ‘Thomas’; ‘Dusa’ (Merensky 2) and ‘Velvick’ outperformed ‘Duke 7’. Comparing horticultural characteristics of the scion, rootstock research with rootstocks grafted to ‘Hass’ has shown to merely improve certain inherent genetically limiting factors, while new generation cultivars have shown to maximise genetically existing attributes. Therefore Allesbeste Nursery decided to discontinue the use of ‘Hass’ and replace it with ‘Maluma’, as the standard for further rootstock evaluation. Under high density (808 trees/ha), the highest yield was recorded with ‘Dusa’, while ‘Bounty’ established best in a replant situation. An ultra-high density trial with 1600 trees/ha grafted on ‘Dusa’, ‘Duke 7’ and ‘Bounty’ is under evaluation. An extensive trial with 24 different clonal rootstocks is to be planted soon.
Key words: clonal rooting technique, tree uniformity, clonal rootstocks, micro cloning, ‘Maluma’.
