2017 ASHS Annual Conference

The supplying of bee hives in avocado orchards to improve pollination and fruit set is highly expensive to the avocado farmers, but for some reason avocado flowers are not very attractive to bees. Therefore, there is a need to find out why. Research has been done on flower structure and functioning, but there are still important aspects that need to be addressed such as the origin and identification of volatiles emitted from the flower. According to Afik et al. (2006), bees have to collect pollen as well as nectar in order for them to visit the male and also the female flowers. If they collect only pollen, they will not visit the female flowering stages and pollination cannot occur. The nectar component is therefore quite important and it could, most possibly, be the nectar that releases volatiles. Afik et al. (2006) also found that avocado nectar and honey were rich in a wide range of minerals including phosphorus and potassium, both of which are repellent to bees, however, the authors have not investigated the volatile compounds from the flowers. Therefore, the aim of this study was to determine the volatile profiles from avocado flowers. The study was done in an orchard on the Experimental farm of the University of Pretoria in South Africa. Four replicates each of male and female stage flowers of ‘Hass’ and ‘Fuerte’ were collected in Petri dishes containing a gel made up of 5% agar, 10% sucrose and 0.05% boric acid and allowed to open. Replicate sample sets (n=4) were sampled at midday and at late afternoon. The headspace of avocado flowers in agar was sampled using an inhouse developed sorptive method (Naudé and Rohwer (2013). After headspace sampling analyses were done by thermal desorption with comprehensive gas chromatography time of flight mass spectrometry (TDS-GC x GC-TOFMS). The data were statistically analysed and means were compared with Fisher's protected least significant test at the 5% level. ‘Hass’ and ‘Fuerte’ flowers had very different volatile chemical profiles. There was also a significant difference between the volatile profiles of male and female flowers within each cultivar. ‘Fuerte flowers had pungent, spicy scents while ‘Hass’ flowers had sweeter scents. In conclusion, we found that avocado flowers produce a large number of volatile compounds which differed between the male and female phases of the flowers and also between the two cultivars that were studied.