Proceedings of The World Avocado Congress III, 1995 61-70 STRATEGIES FOR MAXIMISING AVOCADO PRODUCTIVITY: AN OVERVIEW

Summary The extent of the avocado productivity problem varies regionally. In spite of greater tree vigour in the warm, humid subtropics, sustained yields of 20 to 25 t ha -1 have been achieved. More typical yields in the cooler, semi-arid winter rainfall areas are 8 to 12 t ha -1 . A target sustainable yield with current germplasm of 30 t ha -1 still appears realistic. The majority of growers average less than half of these yields. Causes of low yield are both genetic and climatic, with the latter recently quantified in Israel. A concerted breeding and selection program is necessary to further modify residual evolutionary adaptations which are counter-productive in orchards. Scion requirements should emphasise yield, fruit quality, tree complexity and semi-dwarf growth; rootstocks must have both disease tolerance and impart favourable horticultural characteristics. A growing perception that phosphonate trunk injection technology is less effective than when initially developed requires investigation. , The expanded pheno-physiological growth model of Whiley (1994) sheds new light on productivity constraints in the humid subtropics. Fruit set can be limited not only by temperature and moisture stress, but also by reduced photosynthetic efficiency of over- wintered leaves, and attrition of feeder roots during flowering. Stored carbohydrates become increasingly important as environmental stress increases. Opportunities for managing shoot vigour at critical periods, optimising balanced root, shoot and fruit relationships are discussed. Evidence of crosspollination benefits must be reconciled with orchard practicalities. Orchard design and canopy management strategies remain controversial. Initial high density plantings (200 - 800 tree ha -1 ) are generally accepted, usually with one or two orchard thinnings at onset of crowding. Staghoming, hedgerowing and tree containment by pruning or chemicals, to optimise light interception and canopy bearing throughout the productive life of the orchard, would benefit from ecophysiological research. Guidelines from deciduous orchards are mentioned for possible relevance to avocado.