Boron deficiency of avocado. 1. Effects on pollen viability and fruit set

Abstract

The effect of boron (B) supply on pollen viability was studied using Hass avocado trees (Persea americana) grown in a glasshouse pot experiment with B-deficient soil. Seven rates of B were applied to the soil 12 months prior to anthesis. The number of pollen grains germinating in an artificial minus-B pollen growth medium increased approximately 16-fold when B equivalent to 0.8 or 1.6 g m-2 was applied to the soil. In a field experiment with 5-year old Hass avocado trees of marginal B status (15-29 mg B kg-l dry wt of summer flush leaves), spraying Solubor® onto fully developed panicles at the beginning of anthesis caused a 42% increase in fruit set, but this was not accompanied by a significant increase (p=0,05) in the number of fruit retained following the first fruit drop. Spraying panicles at earlier stages of development had no detectable effect on either fruit set or fruit retention.