The Green Revolution in Punjab began with Mexican dwarf wheats bred by Norman Borlaug, imported in 1966, and with the varieties bred from them at Punjab Agricultural University.
Kalyan Sona and Sonalika came first. PBW 343, released in 1995, became the most widely grown wheat variety in India by 2000 and covered about seven million hectares of the north-west plains by 2002 and 2003, until a new stripe rust race overcame its resistance. Whether it was ever the most widely grown variety in the world cannot be checked here. HD 2967 and PBW 725 followed. Varieties are replaced every few years because the rust races change faster than the plants.
The dwarfing genes are the whole story. A tall wheat given heavy nitrogen grows and falls over. A short wheat given the same nitrogen puts it into grain.
The system that delivers a new variety to a Punjab field, a university breeding programme, a state seed corporation, a network of dealers and the kisan melas, is one of the fastest agricultural extension systems anywhere and it works.
It also means Punjab's wheat is genetically narrow. A rust race that beats the current varieties has a very large uniform crop in front of it, and that has happened before.
The high yielding varieties came from the Mexican dwarf wheats in the 1960s and were adapted at Ludhiana, and the Punjab varieties that followed have been released in a continuous series since.
Each has a working life of about ten years before rust adapts to it, which is why the breeding programme has to run permanently rather than to a conclusion.
The old tall wheats are gone from the fields. They yielded less and lodged in rain, and they also gave straw the animals could eat, which the dwarf wheats do less well.