Breeders develop disease-resistant crops by using various traditional and modern techniques to identify, introduce, and enhance genes that help plants defend themselves against diseases caused by fungi, bacteria, viruses, and other pathogens. The main goal is to produce crop varieties that can withstand infections without heavy reliance on chemical pesticides, ensuring higher yield, lower production costs, and environmental safety.
Here’s how breeders develop disease-resistant crops step by step:
• Identification of Resistance Sources
Breeding starts with finding plants that naturally resist specific diseases. These resistant plants may be wild relatives, landraces, or existing cultivars that show tolerance or immunity to pathogens. Breeders carefully study these plants to locate the genes responsible for resistance.
• Selection and Cross-Breeding
In traditional breeding, resistant plants are crossed with high-yielding but disease-susceptible varieties. The aim is to combine the resistance traits from one parent and the desirable agricultural traits (like yield or quality) from the other. The offspring (hybrids) are then tested to identify those that inherit both resistance and good agronomic performance.
• Screening for Disease Resistance
The new plants are exposed to the target disease under controlled or field conditions to observe how effectively they resist infection. Those that show strong resistance are selected for further breeding and testing.
• Backcrossing and Selection
To improve the stability of disease resistance, breeders repeatedly cross the resistant offspring with the parent variety that has other desired traits. This helps retain the crop’s main features while adding durable resistance genes.
• Use of Marker-Assisted Selection (MAS)
Modern breeders use molecular markers—specific DNA sequences linked to resistance genes—to identify plants that carry those genes. This allows selection at the DNA level, even before the disease appears, saving time and resources.
• Genetic Engineering (Transgenic Approach)
Through biotechnology, genes responsible for disease resistance can be transferred directly into crop plants from other species. For example, a bacterial gene producing Bt toxin has been introduced into cotton and maize to protect them from insect pests. Similarly, resistance genes from one plant species can be inserted into another using recombinant DNA technology.
• Genome Editing Techniques (CRISPR-Cas9)
Newer tools like CRISPR allow precise editing of plant genomes to enhance or introduce resistance traits. Breeders can modify or switch off specific susceptibility genes, making plants naturally immune to pathogens without introducing foreign DNA.
• Induced Mutation Breeding
Exposure of seeds or tissues to radiation or chemicals can create mutations that occasionally lead to disease resistance. These mutants are screened, and the resistant ones are used in further breeding programs.
• Pyramiding of Resistance Genes
To ensure long-term and broad-spectrum resistance, breeders combine multiple resistance genes (R-genes) into a single variety. This prevents the breakdown of resistance caused by evolving pathogens.
• Testing and Field Evaluation
Before release, resistant varieties undergo multi-location trials to confirm their performance under different environmental conditions and disease pressures.
• Examples of Disease-Resistant Crops
– Wheat: Resistant to rust diseases through incorporation of Sr and Lr genes.
– Rice: Resistant to bacterial blight and blast diseases using Xa and Pi genes.
– Potato: Resistant to late blight through gene transfer from wild relatives.
– Tomato: Resistant to viral diseases like Tomato Yellow Leaf Curl Virus (TYLCV).
In summary, breeders develop disease-resistant crops by combining traditional breeding methods with modern molecular and biotechnological tools. By identifying and introducing resistance genes into crop varieties, they create plants that can naturally fight off infections—resulting in healthier crops, reduced pesticide use, and greater food security.