Gene flow in an almond orchard

Area of Science:

• Plant Breeding
• Agricultural Science
• Genetics

Background:

• Commercial almond production relies on cross-pollination due to self-incompatible cultivars.
• Orchard design aims to optimize pollen transfer between pollinating and commercial varieties.

Purpose of the Study:

• To investigate the extent and patterns of gene flow by pollen in a commercial almond orchard.
• To understand the factors limiting cross-pollination and nut set in a specific planting arrangement.

Main Methods:

• Utilized isozyme markers (GPI-2, LAP-1, AAT-1, PGM-1, PGM-2, IDH, G6PD, SDH) to track pollen gene flow.
• Analyzed nut set in a 'two-to-one' planting pattern of Nonpareil and various pollinating almond cultivars.

Main Results:

• Gene flow for nut set was found to be highly restricted, mainly between adjacent compatible trees.
• Pollen transfer decreased significantly on the side of a tree away from the pollinator and further down the row.
• Low nut set (<20%) suggests inefficient cross-pollination despite honeybee presence.

Conclusions:

• The 'two-to-one' planting pattern and honeybee behavior result in limited pollen-mediated gene flow.
• Honeybees may preferentially visit single cultivars, with cross-pollination occurring via infrequent inter-cultivar flights.
• Orchard management strategies may need to address bee behavior to improve almond nut set.