“Genetic basis of resistance to biotic stress and their application in plant breeding” ( Seminar Synopsis)

UNIVERSITY OF AGRICULTURAL SCIENCES, BANGALORE

DEPARTMENT OF GENETICS AND PLANT BREEDING

“Genetic basis of resistance to biotic stress and their application in plant breeding”

Biotic stresses, caused by living organisms like pathogens, insects, and weeds, significantly reduce crop yields of up to 35% globally. Breeding for biotic stress involves the manipulation of two genetic systems: the host and the pathogen. The breeders need to understand the interrelationships between them that have persisted through co-evolution and co-existence.

The genetic resistance to biotic stress in plants is primarily governed by major genes (R genes), minor genes (quantitative trait loci or QTLs), and cytoplasmic genes. The gene-for-gene hypothesis states that for each gene controlling resistance in the host, there is a corresponding gene controlling pathogenicity in the pathogen. This concept is the basis for understanding the genetics of resistance and guides modern breeding for disease-resistant crops.

Vertical resistance provides strong, race-specific defense, but it is often short-lived due to evolving pathogen races. In contrast, horizontal resistance, conferred by multiple genes, offers durable, broad-spectrum protection by reducing disease spread and pest severity. Plants defend themselves through structural barriers (like cuticle, wax, and trichomes) and biochemical responses (phenolics, saponins, alkaloids, and terpenoids) to limit pathogens. They also defend against insect pests through antibiosis, antixenosis, and tolerance.

Plant breeders utilize methods like selection, hybridization, backcrossing, mutation breeding, multilines, gene pyramiding, transgenic approaches, and marker-assisted selection (MAS) to incorporate these resistance traits into high-yielding varieties. Using marker-assisted backcross breeding, the resistance genes Xa21, xa13, Xa4, Pi9, and Pb1 were successfully pyramided into the high-quality rice variety BRRI dhan81. The resulting lines showed enhanced, durable resistance to both bacterial leaf blight and blast diseases, along with desirable yield and grain quality.

The genetic basis of resistance to biotic stress provides a foundation for developing resistant crop varieties. By combining conventional breeding with molecular tools like marker-assisted selection, plant breeders can efficiently incorporate resistance traits for sustainable agriculture.

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REFERENCES

1. FLOR, H.H. (1955). Host-parasite interaction in flax rust-its genetics and other implications. Phytopathology, 45(12): 680-685.

2. NICHOLSON, R.I. (1992). Phenolic compounds and their role in disease resistance. Ann Rev Phytopathol, 30(1): 369-389.

3. LATIF, M.A., HERA, M.H.R., RAHMAN, L., BHUIYAN, M.R., KAYESS, M.O., RASHID, M.M., HASAN, M.A.I., KHAN, M.A.I. AND SAITO, H. (2025). Pyramiding of Multiple Resistance Genes for Bacterial Leaf Blight and Blast Diseases in Premium Quality Rice BRRI dhan81 Through Marker‐Assisted Selection. Plant Pathology, 10(1):1-7.