NEW BREEDING TECHNOLOGIES in cultivar development

What are NBTs?

New breeding technologies refer to a range of innovative techniques that have the potential to revolutionise plant breeding. Of these technologies, genome editing has shown the most promise and has generated the most excitement. The technique refers to the targeted modification of specific genes within the plant genome, allowing for precise and efficient alterations to the genome without the need to incorporate foreign DNA into the plant.

The potential applications of genome editing, and other new breeding technologies in fruit trees and grapevines are vast and varied. They are discussed in the review article listed under “Additional Reading”.

CRISPR is the most widely used genome editing technology. Its system allows scientists to make targeted changes to specific genes, such as introducing beneficial characteristics or eliminating undesirable ones.

CRISPR genome editing was developed a little over a decade ago when it was discovered in bacteria, where it is part of the natural defence mechanism. This technique has since revolutionised science. Scientists have harnessed this system for use in all organisms, finding significant application in medicine and more recently, in agriculture.

CRISPR technology works by utilising a CRISPR-associated protein called Cas, which acts as molecular scissors to cut DNA and a small guide molecule (known as the guide RNA) which directs the molecular scissors to the specific target location.

This cut then triggers the cell’s natural DNA repair mechanisms, which can modify the DNA sequence to obtain the desired trait. The guide targeting system is highly adaptable, enabling scientists to easily reprogram guides that selectively target genes. This, coupled with its accuracy and ability to function without the incorporation of foreign genetic material, have led to a proliferation of CRISPR applications.

In plant breeding, genome editing technologies like CRISPR offer immense potential for improving a large variety of characteristics.

This is demonstrated by the fact that, despite it being a relatively recent development, there are already many instances where crops produced through genome editing have been successfully introduced in global markets (Figure 1).

SATI has funded researchers at Stellenbosch University to investigate the potential use of CRISPR genome editing in developing water stress-tolerant grapevine varieties. Research is underway in the lab of Dr Manuela Campa and Prof Johan Burger, to edit a gene known as MYB60. The gene is involved in regulating the opening and closing of the leaf stomata, allowing for gaseous exchange and transpiration.

The rationale behind this project is that by editing MYB60, so that its activity is decreased, the stomata will remain closed for longer, leading to less transpiration and potential drought tolerance. Different regions of the gene have been chosen as targets for editing to evaluate which of the different changes will result in the desired reduction of MYB60 activity.

Grapevine plants have now been regenerated, and DNA sequencing analysis shows the gene has been successfully edited. This is an exciting first step, and currently analysis is underway to determine if the edits result in prolonged stomata closure, and increased water retention.

Considering the changing climate, traditional breeding methods for fruit trees pose a significant challenge to the industry due to their time-consuming nature. This is particularly problematic in developing countries where access to diverse germplasm collections needed for breeding, may be limited.

NBTs such as CRISPR genome editing offer promising solutions by accelerating fruit tree and grapevine breeding and facilitating the global spread of desirable characteristics.

In apples, researchers in Italy have utilised CRISPR to generate resistance to fire blight and allow for early flowering to accelerate breeding. For citrus, the University of Florida and a start-up company are using CRISPR to develop citrus trees resistant to Huanglongbing (HLB) and citrus canker. Preliminary results showed that the disease did not spread to the edited trees when grafted onto HLB-diseased trees.

While in grapevine, resistance to powdery and downy mildews and cold stress tolerance are currently being implemented through CRISPR-based genome editing. It’s important to acknowledge that although NBTs are generally well-received, certain regions such as Europe still face uncertainties regarding market and public concerns.

Nevertheless, in developing regions such as Asia, Africa, and South America, there is potential for widespread adoption due to anticipated economic benefits and the transformative impact on crop development in the foreseeable future.

Reference

Campa M., S. Miranda, C. Licciardello, J.G. Lashbrooke, L. Dalla Costa, Q. Guan, A. Spök, and M. Malnoy. 2023. Application of new breeding techniques in fruit trees. Plant Physiology https://doi.org/10.1093/plphys/kiad374

For more information, contact Dr Manuela Campa at mailto:mcampa@sun.ac.za