PERFORMANCE OF SIX WALNUT CULTIVARS TRAINED AS FREE AND SEMI-STRUCTURED CENTRAL LEADER SYSTEMS

Persian walnut cultivars increase their productivity using less structured training systems. Six lateral bearing commercial cultivars, 'Chandler', 'Ferjean', 'Fernor', 'Howard', 'Lara' and 'Vina' have been evaluated trained under free (FL) and semi-structured (SSL) central leader systems. The orchard trial has been controlled from planting, 1999, to 2008 harvest. Data of growth and production were recorded on ten trees per cultivars and the training system distributed across five blocks. At the sixth leaf, training was finished (2004). At the end of this juvenile period, at 7 th leaf, the cultivar growth ranking was as expected. 'Chandler', 'Fernor' and 'Vina' showed medium vigour and 'Ferjean', 'Howard' and 'Lara' low vigour. At this age, all the trees were at least 7 m high for any cultivar and training. During the training period the wood pruned weight was up to 50% higher in SSL. Cultivars with upright or spreading growth habits needed more pruning. 'Howard' was the most easily trained, while 'Vina' and `Fernor' were the hardest. The production still favours FL at 8 years. Nuts showed a good size, at least 11 g, in all cultivars and training evaluated. However, it is clearly difficult to maintain enough light in the canopy in the adult phase in some cultivars like 'Lara' or 'Vina'. Orchards of those cultivars need more pruning to maintain marketable nut size.