The Relationship Between Flower and Fruit Abscission and Alternate Bearing of ‘Hass’ Avocado

Abstract

<jats:p>Despite profuse flowering, ‘Hass’ avocado (<jats:italic>Persea americana</jats:italic> Mill.) yields are low because of excessive flower and fruit abscission. Whether the dynamics of flower and fruit abscission are influenced by or contribute to alternate bearing, the production of a heavy on-crop followed by a light off-crop that is characteristic of many avocado cultivars, remains unresolved. The objective of this research was to determine whether abscission of reproductive structures from ‘Hass’ avocado trees during specific developmental stages, including flowering, fruit development, and fruit maturity, was influenced by crop status of the current or preceding year. Abscised reproductive structures were collected from commercially bearing trees during two complete crop years. Flower abscission began at about the same time but peaked 1 month later in the off-crop year compared with the on-crop year. Peak abscission rates were lower during the off-crop year than the on-crop year (compare 1836 ± 403 to 5378 ± 856 flowers per day and 50 ± 18 to 280 ± 23 immature fruit per day, respectively). The off- or on-crop status of the tree did not influence the percentage fruit set, average fruit diameter, or biomass of individual fruit that abscised at similar phenological stages. Furthermore, flower and fruit abscission were not influenced by the number of mature fruit from the previous year's crop. In both years of the research, as immature fruit abscission declined, abscission of the preceding year's crop increased, indicating that the processes were controlled independently. During the study, neither weather conditions nor tree nutrient status were associated with key abscission events. Taken together, these results provide evidence that the previous year's yield does not influence flower or fruit abscission and the seasonal abscission of reproductive structures is an independent process that does not contribute to alternate bearing of ‘Hass’ avocado.</jats:p>

Anatomy and development of fruits of Lauraceae from the Middle Eocene Princeton Chert

“…Extant avocado ( Persea americana Mill.) is known to abscise vegetative and reproductive organs regularly over the growing season, with numerous flowers per inflorescence resulting in few fruits per mature infructescence (Gazit and Degani, 2002; Garner and Lovatt, 2008). Princeton chert plants are typically preserved in situ or parautothochtonously (Cevallos‐Ferriz et al, 1991; Pigg and Stockey, 1996; Stockey, 2001; Little and Stockey, 2006a; Smith and Stockey, 2007).…”

Pistil Starch Reserves at Anthesis Correlate with Final Flower Fate in Avocado (Persea americana)

“…), a member of the Lauraceae, a family included in the early-divergent Magnoliid clade in the angiosperms, is an extreme case of a species with a very low fruit to flower ratio, with less than 1% of the flowers produced able to set fruits due to a massive drop of flowers and developing fruitlets [26–29]. The avocado flower is bisexual having both functional male and female organs although separated in time through a synchronous protogynous dichogamous breeding system that prevents self-pollination promoting outcrossing.…”

“…Although different factors such as temperature [33,34], outcrossing rate [35,36], water and nutrient availability [37] and alternate bearing [29] have been proposed as limiting factors in avocado fruit production, information is still elusive to explain why most flowers prematurely abscise. In avocado, as in other evergreen woody plant species, vegetative and reproductive growth occur simultaneously and, consequently, vegetative and reproductive organs compete for resources provided by either reserve mobilization or photosynthesis [38,39].…”

Ovary starch reserves and pistil development in avocado (Persea americana)

“…Avocado is an extreme case of premature flower and fruit drop because, even after adequate pollination, less than 1% of the flowers produced at anthesis are able to set fruits because of a massive drop of flowers and developing fruitlets (Cameron et al 1952, Garner and Lovatt 2008, Garner et al 2008). Avocado has a complex synchronous protogynous dichogamous flowering biology that promotes outcrossing.…”