MINERAL DISTRIBUTION IN AVOCADO TREES WITH REFERENCE TO CALCIUM CYCLING AND FRUIT-QUALITY

Ca, Mg and K distributions in vigorous and non-vigorous (resulting from moderate Phytophthora cinnamomi infection) cultivar 'Fuerte' and 'Hass' avocado trees, and of Ca in the orchard soil, were determined. Ca concentrations were generally highest in the leaves, bark and small branches and roots, lower in the immature reproductive organs, and very low in the mature fruit and wood. These results are consistent with previous observations of Ca distribution being governed by organ transpiration and auxin export. Mg concentrations showed a similar pattern of distribution to Ca, but differences between organs were less extreme. K concentrations, on the other hand, were highest in the reproductive structures. The leaves contributed the greatest percentage of the tree total for all three elements and the fruit very little (with the exception of K). 'Hass' trees generally contained higher Ca, but lower Mg concentrations than 'Fuerte'; this also applied to the mature fruit flesh. Non-vigorous trees generally showed higher Ca, but lower Mg tissue concentrations than vigorous trees. K concentration was not affected by vigour. A tentative Ca cycle in the avocado orchard is presented, as well as possible ways of modifying fruit mineral composition to favour better fruit quality. © 1990.