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In bad years before the 1950s, a fungal disease could leave a field of Indian wheat with little worth harvesting. Rust diseases were the main reason wheat yields were low and unpredictable, and Benjamin Peary Pal spent decades breeding wheat that could resist them. This post covers how he did it, the Class 12 genetics behind stacking resistance genes, and what students can learn from his patient approach.
Who was B. P. Pal?
His Royal Society biographical memoir, written by M. S. Swaminathan, gives his dates as 26 May 1906 to 14 September 1989. Born Brahma Das Pal, he took the name Benjamin Peary Pal at school in Maymyo, Burma, where his father worked as a medical officer. He studied botany at the University of Rangoon and then, on a scholarship, did a PhD at Cambridge with Frank Engledow on hybrid vigour in wheat, returning in December 1932.
In October 1933 he joined the Imperial Agricultural Research Institute at Pusa in Bihar, renamed the Indian Agricultural Research Institute (IARI) in 1947. He became its Director in 1950, and in May 1965 the first Director General of the reorganised Indian Council of Agricultural Research (ICAR), serving until 1972. He was elected a Fellow of the Royal Society in 1972.
Why was rust such a problem?
The memoir says Pal saw that rust diseases were mainly responsible for low and uncertain wheat yields. Wheat suffers from three: stem rust, stripe rust and leaf rust, each with many biotypes, or races. A variety that resists one race of one rust can still be wiped out by another.
In 1934 he started a breeding programme for rust resistance, working with the mycologist K. C. Mehta. Special facilities to screen plants for rust were set up at Simla, and an off-season nursery was established at Wellington in southern India.
What did his programme produce?
The work gave a series of New Pusa (NP) varieties. NP 710, NP 718, NP 761 and NP 770 combined resistance to individual rusts with good grain and yield. The memoir says that in the severe rust epidemics in Bihar and West Bengal in 1956 and 1957, NP 797, NP 798 and NP 799 stayed healthy and yielded well while local varieties were destroyed.
The key result was NP 809, released in 1954, the first wheat variety with resistance to all three rusts, as well as loose smut. In a talk in April 1955, K. M. Munshi, who had been Union Minister for Food and Agriculture, estimated that Pal's rust-resistant wheats added about Rs 300 million a year to farmers' incomes.
Pal also studied the genetics itself. Working with colleagues, he showed that some wheats carry one set of genes for rust resistance and another that inhibits it, which is why resistance looked dominant in some crosses and recessive in others.
Worked example: stacking two resistance genes
Here is a simplified classroom version with made-up genes. Suppose resistance to stem rust comes from a dominant allele R and resistance to stripe rust from a dominant allele S, on different chromosomes. Variety A is RRss (resists stem rust only) and variety B is rrSS (resists stripe rust only).
F1. Every plant is RrSs, so all resist both rusts. But F1 plants will not breed true.
F2. Self the F1. As in Mendel's dihybrid cross in the NCERT Class 12 chapter Principles of Inheritance and Variation, phenotypes appear in the ratio 9:3:3:1. So 9/16 of F2 plants resist both rusts.
True-breeding plants. Only RRSS plants pass resistance to both to every offspring. Each gene gives RR with probability 1/4, so RRSS is 1/4 x 1/4 = 1/16 of the F2.
In numbers. In 1,600 F2 seedlings you expect about 900 resistant to both, but only about 100 that are RRSS. The breeder has to test the progeny of each resistant plant to find those 100.
Real breeding is harder: there are three rusts, many races, and, as Pal showed, inhibitor genes that can hide resistance. That is why it took two decades to reach NP 809. Our post on Gregor Mendel's pea experiments covers the rules this example uses. If dihybrid ratios are the step that keeps slipping, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can rebuild the idea before you practise.
How did his work lead to the Green Revolution?
Pal later reoriented breeding towards varieties that respond to fertiliser. One result was NP 824, which could yield over 3 tons a hectare. As head of IARI and ICAR he set up the all-India coordinated testing of varieties at many sites. The memoir says results from those trials gave scientists the confidence to recommend importing 250 tons of seed of Mexican semi-dwarf wheats in 1965 and 18,000 tons in 1966. Wheat production rose from 12 million tons in 1964-65 to 17 million tons in 1967-68, a rise of about 42 per cent in three years.
Our posts on Norman Borlaug and M. S. Swaminathan tell the rest of that story.
He also established the IARI Post-Graduate School in 1958 and the Indian Society of Genetics and Plant Breeding, and bred roses and bougainvillea all his life.
What can a student take from Pal's way of working?
Find the real bottleneck. He saw that disease, not just yield, was holding wheat back.
Test widely. Screening at Simla, off-season nurseries and many-site trials turned guesses into evidence.
Expect slow progress. NP 809 came twenty years after he started.
Try it now: in the worked example, what fraction of F2 plants resists stem rust but not stripe rust? Check your answer against the 9:3:3:1 ratio.
