Fruit Development Alters the Vegetative and Reproductive Shoot Growth in 'Hass' Avocado (Persea americana, Mill.)

Avocado, specifically the Hass cultivar, is known for its alternate bearing tendency. This study focused on examining alternate bearing at the single shoot level, across seasons and considering vegetative and reproductive growth.  Four-year old ‘Hass’ avocado trees grafted onto ‘Duke 7’ clonal rootstock in a commercial avocado grove in De Luz, CA, were selected by similar size and bloom intensity.  Individual shoots (N = 260) were tagged and followed for 3 years (2010–12) after dividing the trees into two groups (N = 8 per treatment).  Trees in the first group ("thinned") had all inflorescences manually removed from the tree during the 2010 flowering period.  The second group of trees served as a control and were allowed to flower and set fruit without intervention.  There was a clear difference between the "thinned" and the control group where the former exhibited longer shoots and higher bloom intensities than the latter. Furthermore, we observed that there were very few shoots which set fruit in consecutive years (0.1%). This indicates that alternate bearing in ‘Hass’ avocado occurs at the shoot level rather than on a whole tree level.  We also observed a similar pattern of reduction in shoot length and bloom intensity when shoots did not bear any fruit for two consecutive seasons regardless of treatment. The significance of these results on alternate bearing patterns in ‘Hass’ avocado will be discussed.