Conclusions
The collected data demonstrated that under the conditions during flowering in 2009, there were periods when both functionally male and female flowers could be found within a stand of Hass trees. However, this was not always the case. As the weather regime experienced during flowering was not ideal for effective pollination, it seems reasonable to consider increasing the likelihood of functionally male flowers being open and available for pollinators to visit at the same time as functionally female flowers are open on Hass.
The type B flowers were particularly affected by low temperatures with the female functional stage regularly not being seen during the day. The male functional stage was far more prevalent and often was seen throughout the day. While this will impact on the type B varieties' capacity to set reasonable crops of their own, it does mean they are far more likely to have functionally male flowers open when the Hass flowers are open as functionally female. Therefore, their potential to act as effective cross-polliniser varieties would appear to be enhanced rather than reduced by this flowering delay, particularly given the variable timing of the female functional stage of the Hass flowers. It would appear that provided flowering is occurring at the same time, the likelihood of being a potential cross-polliniser is high.
From the limited dataset, it appears that there are reasonable periods of cross-over between the flowering periods of all the evaluated type B varieties and Hass. However, a closer matching of flowering was found in 2009 with Edranol, Zutano, Ettinger and Sharwil.
Caution should obviously be exercised when interpreting a single year of data, particularly since flowering is so heavily influenced by weather. But while there are limited recordings from this evaluation and they were not contiguous, they generally concur with previously reported findings (Sedgley and Annells 1981, Sedgley and Grant 1983, Sedgley and Alexander 1983). As a result, a reasonable degree of confidence can be had in the results.
Further issues
While the data has demonstrated the potential of the evaluated type B varieties to provide pollen for variety Hass, it has not evaluated whether any cross-pollination occurred or if it is really required. While there were periods when there was no male/female cross-over within the Hass tree and there was cross-over with another variety, this also coincided with periods of weather that were not particularly conducive to good pollination. The availability of pollen may not be the only limiting factor for pollination to occur.
An extra complication, not investigated, is the effect of rain on both pollen release and bee activity. There is also the issue of bee preference to visit either male or female functioning flowers, rather than both, something that was noticed but not effectively monitored.
Acknowledgements
Thank you to David Rankin who collected the flower data for Margaret River. Thanks also to the growers who allowed regular access to their orchards for monitoring of avocado flowers – Wayne Edwards, Dean French, William French and the Manjimup Horticultural Research Institute.
This report was previously published as Appendix H in ‘Improving technology uptake in the WA avocado industry’, a final report for Horticulture Australia Limited project AV06002 funded by the Agricultural Produce Commission Avocado Growers Committee, Horticulture Australia Limited and Department of Agriculture and Food, Western Australia. The complete final report is available electronically via Avocados Australia web site (member services login) or Horticulture Innovation Australia (abstract or hard copy for purchase).
References
The following references and many more on the subject are available electronically via avocadosource.com, an extensive internet database of avocado information from around the world — hosted by the Hofshi Foundation.
Sedgley, M and Annells, CM 1981, 'Flowering and fruit-set response to temperature in the avocado cultivar Hass’, Scientia Horticulturae, vol. 14, pp. 27-33.
Sedgley, M and Grant, WJR 1983, 'Effect of low temperature during flowering on floral cycle and pollen tube growth in nine avocado cultivars', Scientia Horticulturae, vol. 18, pp. 207-213.
Sedgley, M and Alexander, DMcE 1983, 'Avocado breeding research in Australia', California Avocado Society 1983 Yearbook, vol. 67, pp. 129-140.