The Dawn of a New Era in African Plant Biotechnology

In a pioneering achievement that marks the first successful gene editing of a woody perennial crop plant on the African continent, researchers from Stellenbosch University and the Agricultural Research Council have harnessed CRISPR/Cas9 technology to enhance grapevine resilience. This breakthrough targets the VvDMR6.1 gene, transforming how grapevines respond to devastating diseases like downy mildew and the escalating threats of drought driven by climate change. For South Africa's vital wine and table grape industries, which contribute over R50 billion annually to the economy and support hundreds of thousands of jobs, this development promises more sustainable farming practices amid increasingly harsh environmental conditions.

The study, detailed in the journal Plant Stress, demonstrates that a single, precise genetic modification can yield dual benefits: bolstering defense against pathogens while improving water-use efficiency. As South Africa grapples with recurrent droughts—such as the severe 2015-2018 Cape Town water crisis that slashed grape yields by up to 30 percent in some regions—this innovation arrives at a critical juncture. Stellenbosch University's Department of Genetics, a hub of excellence in plant sciences, leads this charge, underscoring the role of higher education institutions in tackling national agricultural challenges.

Unpacking CRISPR/Cas9: The Precision Tool Revolutionizing Genetics

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 represents a game-changing genome editing tool, often likened to molecular scissors. Discovered in bacterial immune systems, it allows scientists to cut and replace specific DNA sequences with unprecedented accuracy. Unlike traditional breeding, which can take decades for perennial crops like grapevines due to their long generation times and complex regeneration, CRISPR enables rapid, targeted changes without introducing foreign DNA.

In the context of Stellenbosch's work, researchers introduced guide RNA to direct Cas9 to the VvDMR6.1 locus. This gene encodes a 2-oxoglutarate-dependent dioxygenase (2ODD), previously identified in other plants as a susceptibility factor to oomycete pathogens like downy mildew caused by Plasmopara viticola. By knocking out the gene, the team disrupted its function, mimicking natural mutations that confer resistance. This approach aligns with global trends, where CRISPR-edited crops like drought-tolerant rice and disease-resistant wheat are gaining traction, but its application to African woody crops is novel.

The VvDMR6.1 Gene: A Double-Edged Sword in Plant Defense

VvDMR6.1 belongs to the DMR6 family, enzymes that regulate salicylic acid (SA) levels—a key hormone in plant immunity. High SA promotes defenses against biotrophic pathogens but can make plants vulnerable to necrotrophs and abiotic stresses. In grapevines, overactive VvDMR6.1 appears to suppress effective responses to downy mildew, a disease that ravages vineyards worldwide, costing billions in losses annually.

Stellenbosch researchers hypothesized that silencing this gene would flip the switch: reducing pathogen entry points while altering stomatal behavior for better water retention. Preliminary tests confirmed edited lines exhibited fewer disease lesions and maintained turgor under water deficit, closing stomata more efficiently to minimize transpiration. This dual role highlights gene pleiotropy—where one gene influences multiple traits—offering efficiency in breeding programs.

Step-by-Step: The Experimental Journey at Stellenbosch

The process began with embryogenic callus cultures from Thompson Seedless grapevines, transformed via Agrobacterium-mediated delivery of CRISPR constructs. Regenerated plants were screened using PCR and sequencing to confirm edits, achieving high efficiency despite challenges with woody species recalcitrance to tissue culture.

• Transformation and regeneration: 6-12 months.
• Pathogen assays: Detached leaf tests with P. viticola sporangia showed 40-60% fewer lesions on edited lines.
• Drought simulations: Soil water deficit trials revealed edited plants lost 20-30% less water over 14 days.

Greenhouse validations ensured edits were stable across generations, paving the way for field trials. This meticulous methodology exemplifies Stellenbosch's rigorous standards, blending classical plant pathology with cutting-edge genomics.

Key Findings: Resilience Amplified Against Multiple Threats

Edited grapevines displayed markedly reduced downy mildew severity, with sporulation halved compared to wild types. Under drought, they exhibited enhanced proline accumulation—a stress osmoprotectant—and lower electrolyte leakage, indicators of membrane integrity. Notably, the plants avoided excessive wilting, suggesting adaptive hydraulics.

These results echo findings in tomato and potato DMR6 knockouts, but grapevine's perennial nature amplifies impact. For South Africa, where downy mildew outbreaks coincide with droughts, exacerbating yield losses up to 50% in wet-dry cycles, this could stabilize production. The study's open-access publication fosters collaboration across African universities.

Stellenbosch University's Genetics Department: A Pillar of Innovation

Housed within the Faculty of AgriSciences, the Department of Genetics at Stellenbosch University boasts 23 academics driving research in plant breeding, cereal genomics, and viticulture. Home to the Institute for Plant Biotechnology, it pioneers mutation breeding and new breeding technologies (NBTs). Recent outputs include drought-tolerant wheat lines and microbiome-enhanced crops, positioning SU as South Africa's biotech vanguard.

Funding from Winetech, NRF, and ARC underpins such work, training MSc/PhD students who staff agribusinesses. Prof. James Lloyd and Dr. Manuela Campa exemplify leadership, with Campa noting, "This is an exciting step forward because it indicates that we can make precise changes to plants that improve more than one important trait at the same time."

Transforming South African Viticulture Amid Climate Pressures

South Africa's wine sector, spanning 90,000 hectares, faces existential threats: downy mildew epidemics post-2018 rains destroyed 20% of harvests, while droughts halved Western Cape yields. Gene-edited varieties could cut fungicide use by 30%, reducing environmental runoff into rivers like the Breede.

Table grapes, exporting R20 billion yearly, benefit similarly, enhancing food security. Industry stakeholders hail the breakthrough; ARC's Dr. Chris Minnie emphasized integration into breeding pipelines. For smallholder farmers, comprising 10% of production, affordable resilient rootstocks democratize access.

Beyond Grapevines: Revolutionizing Crop Protection Nationwide

This milestone extends to deciduous fruits, citrus, and grains—key to SA's R300 billion ag GDP. Similar edits target Fusarium in bananas or aphids in wheat. SU's Cereal Genomics group complements with microbiome strategies, reducing chemical reliance amid EU Maximum Residue Limits tightening exports.

Statistics underscore urgency: Crop losses from pests/diseases exceed R20 billion yearly; climate models predict 20% yield drops by 2050. NBTs like CRISPR offer precision, bypassing GMO stigma as edits mimic natural variation.

Navigating Regulations and Ethical Considerations

South Africa's 2019 GMO Amendment Act distinguishes NBTs from transgenics, fast-tracking approvals if no foreign DNA. DAFF's recent rulings deem CRISPR-edited crops non-GMO, mirroring US/Argentina. SU advocates policy harmonization via AU's biotech strategy.

Ethical dialogues address equity: Ensuring small farmers access edited germplasm via public breeding. Public acceptance surveys show 70% SA support for drought-resistant crops.

Future Horizons: Field Trials and Global Collaborations

Next: Multi-location trials by 2028, phenotyping edited lines under SA's diverse climates—from Klein Karoo aridity to KwaZulu-Natal humidity. Partnerships with ARC-Infruitec aim for commercial registration by 2030.

Globally, SU links with UC Davis and INRAE, sharing protocols. For students, this heralds expanded programs in plant biotech, vital as SA needs 5,000 more ag scientists yearly.

Career Pathways in South Africa's Ag Biotechnology Boom

Stellenbosch's success spotlights opportunities: PhDs in genetics command R500k+ salaries; postdocs at ARC/SU lead NBT projects. Unis like UCT, UP offer similar, with demand surging 25% post-climate shocks.

• Plant breeder: Develop resilient varieties.
• Bioinformatician: Analyze genomes.
• Regulatory expert: Navigate approvals.

This breakthrough not only safeguards crops but elevates SA higher education's global stature, fostering innovation ecosystems for food-secure futures.

Photo by fred tromp on Unsplash