Why wheat genetics matters
Wheat is one of the pillars of global food security: it provides about 18–20% of calories and proteins in the human diet worldwide, with much higher shares in North Africa and Western Asia. Understanding how varieties evolve and which tools breeders use is crucial for yields, quality, and the resilience of supply chains.
A giant genome
Bread wheat (Triticum aestivum), the species from which we obtain flour for bread, pizza, and pastries, has a unique feature: its DNA is huge and extremely complex.
Unlike humans, who have two copies of each chromosome (one maternal and one paternal), bread wheat has six copies. This makes it hexaploid. This condition is the result of its evolutionary history: around 9,000 years ago, near the dawn of agriculture, a domesticated tetraploid wheat naturally crossed with a wild grass called Aegilops tauschii. From this encounter, modern bread wheat was born, with three sets of chromosomes (A, B, and D).
The outcome is an enormous genome, about five times larger than the human genome (around 16 billion DNA letters). Not only that: about 85% of this DNA consists of repetitive sequences, known as transposable elements, which make it much harder to read and interpret the genetic code.
For decades, this complexity made it nearly impossible to study wheat DNA in detail or use it effectively in breeding programs. The real breakthrough came in 2018, when the international consortium IWGSC published the first reference genome of bread wheat. Later, with the development of pangenomes—maps comparing the DNA of many different varieties—researchers were finally able to pinpoint genes useful for increasing yields, enhancing disease resistance, or improving tolerance to drought.
Today, these tools pave the way for advanced techniques such as marker-assisted selection, genomic selection, and genome editing with CRISPR, which make wheat breeding far more targeted and efficient than in the past.
Durum vs bread wheat: two different evolutionary paths
Durum wheat (Triticum durum), used for pasta, and bread wheat (Triticum aestivum), used for bread and pastries, have distinct genetic histories. Durum has two sets of chromosomes (AABB), and its DNA was fully “decoded” in 2019 with the variety Svevo, which helped researchers identify genes influencing semolina quality and disease resistance.
Bread wheat, with its three sets of chromosomes (AABBDD), is even more complex. Thanks to pangenomes, scientists now know that there is enormous genetic variability: some varieties carry genes that others completely lack. This diversity is a powerful resource for improving yields and adaptability.
From the Green Revolution genes to modern adaptations
In the 1960s, the so-called Green Revolution introduced genes that made wheat plants shorter (Rht-B1b and Rht-D1b). Shorter plants were less likely to lodge (fall over) in the wind or rain, increasing production stability. However, these genes also had side effects, such as smaller kernels and reduced nitrogen-use efficiency.
Today, researchers are exploring more refined solutions, such as modulating plant hormones to achieve compact yet high-yielding plants. In addition, genes controlling vernalization (the need for cold to flower) and photoperiod sensitivity (response to day length) are crucial for adapting wheat to warmer climates or shorter growing seasons.
The secret of bread and pasta lies in the glutenThe quality of gluten is key to different uses of wheat. Some proteins (glutenins) make dough elastic, while others (gliadins) give it stretchiness. The balance between these components explains why some flours are ideal for bread and others for pasta or pastries.
Another important trait is grain hardness, controlled by the puroindoline genes. This determines how the grain fractures during milling and therefore what type of flour is produced.
The modern breeding toolbox
Today, wheat breeders have access to a wide array of tools:
- Molecular markers: allow tracking of desired genes in the lab, speeding up selection.
- Genomic selection: uses thousands of markers spread across the DNA to predict a variety’s performance even before field testing.
- Speed breeding: with artificial light and controlled greenhouses, up to six generations of wheat per year can be obtained instead of just one.
- Doubled haploids (DH): techniques that produce genetically “fixed” plants in a single generation.
- Mutagenesis and TILLING: create new variants without adding foreign genes, still useful today to broaden diversity.
Disease resistance: beyond short-term fixes
Traditionally, researchers introduced “specific” genes to protect wheat against diseases. But pathogens evolve quickly and often overcome these defenses. That’s why scientists now also focus on durable resistance genes like Lr34 and Lr67, which protect against multiple pathogens (rusts, powdery mildew) and remain effective over time.
GMOs in wheat: a rarity
Unlike maize and soybeans, genetically modified wheat has never reached widespread cultivation. The first real case is HB4® wheat, developed in Argentina with a sunflower gene for drought tolerance. It is already grown in Argentina and Brazil, but its acceptance in international markets remains contested, especially in Europe, where GMO regulations are still very strict.
Gene editing: CRISPR as a silent revolutionWith CRISPR/Cas technology, scientists can modify wheat DNA with extreme precision, even though it carries six copies of each gene. Some concrete results include:
- knocking out the TaMLO gene, which makes plants resistant to powdery mildew;
- reducing gliadins, proteins that contribute to gluten sensitivity, while maintaining flour quality.
In many countries, gene editing is regulated differently from traditional GMOs, although the European Union still takes a very cautious stance.
Biodiversity as a resource
New genetic maps and the study of wheat’s wild relatives are giving access to “forgotten” genes: tolerance to heat and drought, better nitrogen-use efficiency, and disease resistance. Gene banks managed by institutions such as ICARDA and CIMMYT are essential treasuries for the future of wheat breeding.
Not just a question of GMO or non-GMO
Wheat improvement cannot be reduced to the dichotomy “GMO yes or no.” In reality, today’s breeders use a combination of approaches: traditional crosses, marker-assisted selection, speed breeding, and gene editing. Each method has strengths and limits, and the choice depends on the trait to be improved, the timeframe, market regulations, and social acceptance.
Sources:
- Genomi & pangenomi: IWGSC (2018) Science (genoma di riferimento del tenero); Walkowiak et al. (2020) Nature (pangenoma tenero); Maccaferri et al. (2019) Nat Genet (genoma del duro).
- TE & complessità genomica: Wicker/Appels in review open-access (TE ~85%).
- Origine/esaploidia: Pont et al. (2022) Evolution and origin of bread wheat (review open-access).
- Green Revolution & adattamento: Jobson et al. (2019) Frontiers Plant Sci; Pearce (2021) J Exp Bot; Kippes et al. (2015).
- Qualità tecnologica: Li et al. (2020) HMW-GS (open-access); Morris (2002) puroindoline/Ha locus.
- Genomic selection & HTP: Juliana et al. (2020) Frontiers Plant Sci; Sun et al. (2019) The Plant Genome.
- Speed breeding: Watson et al. (2018) Nature Plants; protocollo in Nat Protocols.
- DH/TILLING: Guan et al. (2024) Agronomy (DH grano×mais); Lantos et al. (2023) (anther culture); Uauy et al. (2009) BMC Plant Biol (TILLING)
- Resistenze durature: Krattinger et al. (2009) Science (Lr34); Moore et al. (2015) Nat Genet (Lr67).
- CRISPR nel grano: Wang et al. (2014) Nat Biotechnol (TaMLO); Sánchez-León et al. (2018) Plant Biotechnol J (α-gliadine); Yu et al. (2024) Plant Biotechnol J (γ/ω-gliadine).
- OGM HB4: Gupta et al. (2024) Trends Biotechnol; ISAAA GM Approval Database (stato autorizzazioni).
- Regole & diritti: UPOV 1991 (testo ufficiale); Direttiva UE 98/44/CE; pagine EFSA su GMO.