Abstract
Pollination is limiting for avocado production. We examined whether adding bumblebees (BBs; ca. 10 hives/ha) to conventional honeybees (HB; 5 hives/ha) would improve ‘Hass’ avocado pollination and yields. A preliminary trial (2017/18) in an avocado orchard with four consecutive rows of ‘Hass’ followed by one row of ‘Ettinger’ serving as a pollenizer (20% ‘Ettinger’) showed a considerable increase in ‘Hass’ yield in rows adjacent to (up to 80 m from) the BB hives vs. distant rows (=controls). In 2018/19, the trials were extended to three additional orchards. A significant yield increase was obtained in the BB hive-adjacent trees compared to BB hive-distant ones. Similar results were obtained in 2019/20, in experiments conducted throughout the country. The SNP analysis, to determine the parents of ‘Hass’ fruit at varying distances from the BB hives, showed no differences in the cross-pollination rate (‘Hass’ × ‘Ettinger’). However, pollination rates and the number of germinating pollen grains per stigma decreased with distance from the hives, and correlated to the negative gradient in yield. Taken together, our data suggest that adding BB hives to ‘Hass’ avocado orchards, at ca. 10 hives/ha resulting in 0.5–1.0 BB visits/tree per min, increases pollination and, accordingly, total yield.
Highlights
Insufficient pollination is a major limiting factor for avocado (Persea americana Mill.) fertility [1,2,3]
Afic et al [8,9] reported that the low attractiveness of the flowers to the bees is due to the nectar composition, rather than the sugars within it; they showed that avocado nectar is relatively rich in a wide range of minerals, primarily potassium and phosphorus
An average of 410 fruit per tree was obtained in trees located about 60 m from the BB hives, and the number of fruit decreased linearly as the distance increased
Summary
Insufficient pollination is a major limiting factor for avocado (Persea americana Mill.) fertility [1,2,3]. Similar results were found in Asian pear (Pyrus pyrifolia) pollinated in excess [25] Keeping this notion in mind, in the last few years we decided to test the efficacy of BBs as a supplement to HBs in Israel, in orchards of deciduous fruit trees such as pears and apples [19,20]. The impressive increase in cross-pollination of that species resulted in an increase in the number of seeds in the fruit, which led to a significant improvement in the number of fruit per tree and fruit size This approach has become commercial practice in apple orchards in recent years. A fruit species that can self-fertilize like avocado but is very attractive to HBs [26], we found that the addition of BBs to the orchards results in an increase of about 50% in fruit set and yield [27]. All orchards included only ‘Hass’ as the main cultivar and ‘Ettinger’ as the pollenizer, in different ratios and arrangements [28] (see Table 13)o.f 17
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