Outcrossing Rate and Fruit Yield of Hass Avocado Trees Decline at Increasing Distance from a Polliniser Cultivar

Optimal fruit production from many tree crops relies on the transfer of cross-pollen between trees of different cultivars rather than the transfer of self-pollen between trees of the same cultivar. However, many orchards are established with wide blocks of single cultivars, which can result in high percentages of self-fertilised fruit and sub-optimal yield and quality. We aimed to determine whether outcrossing rates and yield of Hass avocado fruit decline with increasing distance from polliniser trees of cultivar Shepard and whether selfed fruit are smaller than outcrossed fruit. Outcrossing rates declined from 49% at six trees (40 m) from a block of Shepard trees to 30% at thirty trees (160 m) from a block of Shepard trees. Tree yield across this distance declined by 44% as a result of a 69% decline in the number of outcrossed fruit per tree, without a significant decline in the number of selfed fruit per tree. Outcrossed Hass fruit were 12% heavier than selfed Hass fruit, with 3% greater diameter and 5% greater length. The study results demonstrate the importance of interplanting Type B avocado pollinisers closely with Type A Hass trees to increase fruit yield and size.