The Impact of Outcrossing on Yields of ‘Hass’ Avocado

Hass' avocado (Persea americana Mill.) is characterized by excessive flower and fruit abscission, resulting in extremely low fruit set. Low outcrossing rates might be a factor contributing to low yields. It is hypothesized that self-fertilized flowers and resulting fruit abscise at a much higher rate than fruit that are the product of outcrossing. However, significant relationships between outcrossing rates and yields have only been established in a few avocado studies. The objective of this research was to investigate the importance of outcrossing to yield in a commercial 'Hass' orchard containing 'Bacon', an effective pollinizer of 'Hass'. Microsatellite markers were used to determine the rate of outcrossing of fruit persisting to harvest on 'Hass' trees. Experiments were conducted during sequential on- and off-crop years. During both years, outcrossing rates were not related to yield or alternate bearing. These results indicate that outcrossing was not the primary factor affecting flower and fruit persistence and ultimately yield in this orchard for the two sequential years of this research. Avocado and many other subtropical fruit tree crops are characterized by excessive flower and fruit abscission. Thou- sands of avocado flowers and immature fruit abscise in a single season (Cameron et al., 1952; Garner and Lovatt, 2008; Inoue and Takahashi, 1990; Lahav and Zamet, 1975; Slabbert, 1981), resulting in extremely low fruit set (