🧬 Rice — Breeding Methods and Varieties

Rice improvement in self-pollinated systems relies on method discipline, from pedigree selection to targeted backcrossing and hybrid systems. This lesson summarizes method logic and flagship Indian outcomes.

---

Breeding Methods in Rice

Since rice is predominantly self-pollinated, the following breeding methods are employed:

Pedigree Method

This is the most widely used method. Individual plants are selected from segregating F2 populations and their progenies are tracked through subsequent generations. This method was used to develop landmark varieties like Jaya, IR36, and Pusa Basmati 1121.

Bulk Method

Entire F2-F5 populations are advanced in bulk, and selection begins only in later generations. Suitable when the objective is to recover transgressive segregants for quantitative traits such as yield.

Backcross Breeding

Used to transfer a single gene (e.g., disease resistance) from a donor parent into an elite recipient variety while retaining the recurrent parent's agronomic background. Marker-assisted backcrossing (MABC) was used to introgress the SUB1 gene for submergence tolerance into Swarna, IR64, and other mega-varieties.

Mutation Breeding

Physical mutagens (gamma rays, X-rays) and chemical mutagens (EMS, sodium azide) are used to induce heritable changes. Notable mutant varieties include PNR-381 and Basmati 370 derivatives. India is among the leading countries in the release of rice mutant varieties.

---

Hybrid Rice

Hybrid rice exploits heterosis (hybrid vigour) for yield gains of 15-30% over the best inbred varieties. The three-line system based on cytoplasmic male sterility (CMS) is the primary commercial approach:

• A line (CMS line) — male sterile, used as the seed parent.
• B line (Maintainer) — fertile, maintains the A line.
• R line (Restorer) — carries fertility-restoring (Rf) genes; crossed with the A line to produce fertile F1 hybrids.

The two-line system based on environment-sensitive genic male sterility (EGMS) — photoperiod-sensitive (PGMS) or thermo-sensitive (TGMS) — simplifies hybrid seed production by eliminating the need for a maintainer line.

---

Important Varieties

Variety	Special Features
IR8	First semi-dwarf, high-yielding (Green Revolution)
Jaya	First Indian high-yielding variety
Pusa Basmati 1121	Extra-long grain, high export value
Swarna Sub1	Submergence tolerant (SUB1 introgression)
DRRH-2, PA 6201	CMS-based commercial hybrids
Samba Mahsuri (RP Bio 226)	Bacterial blight resistant (Xa21 gene via MAS)

Hybrid rice research in India is coordinated by the Indian Institute of Rice Research (IIRR), Hyderabad and ICAR-DRR.

---

Summary Cheat Sheet

Quick Recall Points\n- Self-pollinated crop: pedigree, bulk, backcross, and mutation are core pipelines.\n- SUB1 introgression is a classic marker-assisted backcross success.\n- Hybrid rice uses A, B, and R lines in the three-line CMS system.\n\n### Exam Traps\n- Hybrid rice is not produced by simple varietal mixing; sterility-restoration genetics are mandatory.\n- Backcross breeding targets specific gene transfer while retaining elite background.

References

2 sources • [1] [2]

[1]

ICAR eCourse: GPBR 213 Crop Improvement-I (Kharif Crops)

Book

[2]

ICAR Crop-specific research bulletins (IIRR, IIMR, IIMR Sorghum, ICRISAT, CICR, SBI, CRIJAF)

Website