Screening mainstream plum cultivars for the duration of the effective pollination period and other factors influencing successful fruit set

Hortgro compiled a 2019-2024 Hortgro Science Strategic Plan. One of the gaps identified by the stone fruit industry was a limited understanding of factors influencing successful plum fruit set. The aim of this study is to determine the duration of the effective pollination period (EPP) of mainstream plum cultivars produced in the Western Cape.

Nine plum cultivars of commercial importance were selected for the study: African Delight, Angelino, Fortune, Laetitia, Songold, Ruby Star, Ruby Sun, Ruby Crisp and Sapphire.

Conducted controlled pollination during flowering season and monitored fruit: 100 bearing units with ten reproductive buds were covered when flowers were at balloon stage. At full bloom stage ten flower bunches on ten trees are pollinated for ten consecutive days. Determine fruit set 12, 21 and 42 days after pollination of the last pollination episode.

The trial sites were on farms with well-maintained orchards in Worcester, Robertson and Bonnievale areas and weather data was collected for these trial areas.

Climate did differ between seasons and consequently influenced the flowering times and time of controlled pollinations.

However, it seems that EPP is not dependent on season, but rather seems to be cultivar dependent since EPP was constant during 2021, 2022 and 2023 seasons.  The success of pollination is affected by wind, rain and heat thus special care was taken to reduce the effect on pollination by protecting flowers. Flowers were also covered with gauze bags before and after pollination.

Protocol was developed to determine EPP of plum cultivars and revealed that Laetitia had the longest EPP and Ruby Crisp and Songold the shortest.

Climate did not have a significant influence on EPP since pollination was done by hand, except for high temperatures that preceded 2023 pollinations of Sapphire. Suspect Songold’s EPP is influenced by climate since Laetitia and Songold are planted in the same orchard, but pollination success differs.

A screening protocol was developed to determine the duration of the effective pollination period for mainstream plum cultivars in the South African industry. More cultivars should be tested to assist producers when selecting a cultivar for establishment in a specific environment.

The EPP determination can be provided as a service to cultivar owners. It would be recommended that the evaluation be repeated over a few years.