RESEARCH & EVENTS
44
Self-pollination , self-compatibility and self-fertility in almonds
By Cassandra Collins , Almond Breeder , University of Adelaide
THE confusion around self-pollination , self-compatibility , and self-fertility in almonds comes from the specific differences between these terms . They all relate to how almonds reproduce but mean slightly different things . Self-pollination refers to the physical process of transferring pollen from the anther ( male part ) to the stigma ( female part ) within the same flower or plant ( Figure 1A ). Almonds normally rely on insects like bees for cross-pollination because they are not naturally efficient at selfpollination . Even in almond varieties that are selfcompatible and self-fertile , pollinators often help by moving pollen between flowers on the same tree or across different trees , improving pollination and potentially increasing yield . Self-compatibility is a plant ’ s genetic ability to use its own pollen for fertilisation ( Figure 1B ). In almonds , even when a flower receives pollen from the same plant , the pollen must be genetically compatible with the flower ’ s reproductive structures for fertilisation to be successful . This trait allows certain almond varieties to set fruit without needing pollen from different varieties , however , pollinators can still contribute to improved fruit set and higher yields . Traditional almond varieties are selfincompatible , meaning that even if they receive their own pollen , it will not result in fertilisation due to genetic mechanisms that prevent it . Almond flowers are typically bisexual , with both male and female reproductive parts in the same flower . The stamens ( male organs ) produce pollen , and the pistil ( female organ ) contains the stigma ( where pollen is received ), style , and ovary . Self-compatible almond varieties tend to have more efficient pollen transfer within the same flower or from flower to flower on the same tree . This is particularly beneficial in almond flowers where the stigma is located close enough to the stamens to receive pollen directly ( Figure 1C ),
In A Nutshell - Winter 2024 Vol 25 Issue 2
Figure 1 . Illustration of self-pollination ( A ), self-compatibility and self-incompatibility ( B ), flower morphology ( C ) and self-fertility ( D ) in almonds . Collins , C . ( 2024 ) https :// BioRender . com / p43x770
First stage of self-fertile plantings at ACE Orchard
The ABA has planted the first stage of its single block plantings of self-fertile varieties at the Almond Centre of Excellence . This trial will help to demonstrate the benefits and cost efficiencies possible in planting self-fertile almond varieties in single blocks , as opposed to the traditional plantings with alternative rows of pollinators and Nonpareil . Insect exclusion nets will be installed before flowering to prevent cross pollination and provide the opportunity to measure the ability of each flower to set fruit using its own pollen or pollen from flowers on the same tree and without insect assistance .
reducing reliance on cross-pollination from another tree . Morphological traits in self-compatible varieties may also include slightly altered stamen and pistil arrangements that facilitate easier self-pollination , although the differences are subtle . Understanding these morphological features can help producers optimise their orchard management practices , for both self-compatible and traditional varieties .
This knowledge is also useful for improving yield consistency in variable weather conditions by understanding how almond flower structure interacts with environmental and pollinator influences . Self-fertility refers to a plant ’ s ability to produce fruit and seeds using its own pollen without requiring crosspollination from another plant ( Figure 1D ). Most traditional almond varieties are not self-fertile , meaning they require pollen from another almond tree ( a different variety ) to fertilise their flowers and set fruit . However , newer almond varieties ( such as ‘ Carina ’ or ‘ Independence ’) have been bred for self-fertility , allowing them to produce almonds without needing a second pollinator variety . While self-fertile varieties can produce almonds without a polliniser , yield can still fluctuate based on environmental factors and pollinator presence . Pollinators increase yield consistency , so including them in self-fertile orchards is still important . In almonds , both self-fertility and self-compatibility are important traits in modern breeding programs to improve orchard efficiency , while self-pollination refers more to the physical process of how pollen reaches the stigma .