🧬 Wheat — Breeding Methods, Rust Resistance, Quality

This lesson focuses on how wheat breeders combine method, resistance genetics, and end-use quality to release stable high-performing varieties.

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Breeding Methods

Wheat is a self-pollinated crop with natural cross-pollination of less than 1%. The most commonly used breeding methods include pedigree method, where individual plant selections are made in segregating generations with detailed pedigree records maintained from F2 onwards. The bulk method is used when large populations need to be advanced economically. The backcross method is particularly effective for transferring specific genes such as rust resistance into established high-yielding cultivars. Shuttle breeding, pioneered by Dr. Norman Borlaug at CIMMYT, involves growing alternate generations at two contrasting locations (e.g., Toluca and Ciudad Obregon in Mexico) to accelerate generation advancement and select for wide adaptation and photoperiod insensitivity. In India, shuttle breeding is practiced between Delhi (north) and Wellington (south). Mutation breeding has produced notable varieties such as Sharbati Sonora (amber grain colour from Sonora 64). Modern approaches include marker-assisted selection (MAS) and genomic selection for accelerating genetic gains.

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Rust Resistance Breeding

Rust diseases are the most destructive biotic constraints in wheat. Stem rust resistance genes include Sr2 (durable, adult plant resistance from Hope), Sr31 (from 1BL/1RS translocation of Secale cereale), and Sr38. Leaf rust resistance is conferred by genes like Lr24, Lr28 (from Aegilops species), Lr34 (durable, pleiotropic with Yr18 and Sr57), and Lr67. Stripe rust resistance genes include Yr5, Yr10, Yr15, and the durable adult plant resistance gene Yr18. Gene pyramiding through marker-assisted backcrossing (MABC) is the preferred strategy for combining multiple resistance genes in a single cultivar. The linked markers such as csLV34 for Lr34/Yr18 are routinely deployed in Indian wheat breeding programmes. Varieties like HD 2967, HD 3086, and DBW 187 carry multiple rust resistance genes.

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Quality Parameters

Wheat quality depends on end-use. For bread wheat, high protein (>12%), strong gluten, high sedimentation value (SDS test), and grain hardness are desirable. For chapati quality (important in India), medium protein, extensible gluten, high water absorption, and amber grain colour are preferred. The HMW glutenin subunits (encoded at Glu-A1, Glu-B1, Glu-D1 loci) are major determinants of dough strength. Subunit combinations 1, 7+8, 5+10 confer superior bread-making quality. For durum wheat (pasta), high yellow pigment content (carotenoids), strong gluten, and vitreous grain are important. Biofortification efforts target increased iron (>40 ppm) and zinc (>35 ppm) content. Varieties like WB 02 and MACS 4028 are biofortified releases from India.

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Summary Cheat Sheet

Quick Recall Points

• Wheat is predominantly self-pollinated; key methods are pedigree, backcross, and shuttle breeding.
• Durable rust resistance often uses Lr34/Yr18/Sr57-linked strategies.
• Bread quality depends strongly on HMW glutenin subunits and protein level.

Exam Traps

• Lr34 is durable adult-plant resistance; do not classify it as short-lived race-specific resistance.
• Chapati quality and bread quality do not always need the same gluten profile.

References

2 sources • [1] [2]

[1]

Wheat Science — N.E. Borlaug and CIMMYT literature

Book

[2]

ICAR-IIWBR wheat improvement resources

Official