A new weapon for wheat growers fighting rust

- multilines in India

An alternative approach to providing farmers with a means of stabilized resistance against the perennial threat of rust has reached field level in major wheat-growing areas of India. A year ago, the Punjab Department of Agriculture and Punjab Agricultural University released for distribution to farmers about 4 000 small packets of the seed of a new multiline variety of wheat expected to provide durable resistance to yellow and brown rusts. From this seed-multiplication programme, large quantities of seed are available for the 1978/79 crop year.

As in many other parts of the world, wheat growers in India have adopted semidwarf varieties on an extensive scale because of their high yield potential as compared with the old, tall varieties. One result has been the tendency to monoculture of a few varieties, creating a situation in which virulent forms of plant disease pathogens may multiply to epidemic proportions. A striking example is the Kalyasona variety developed from a Mexican cross, 8156 from CIMMYT. Kalyasona was very popular in India for a few years until it became susceptible to yellow and brown rusts.

In view of this, work was initiated at the Punjab Agricultural University to develop multiline varieties within the genetic background of Kalyasona. The concept of multiline varieties is based on the diversification of component lines with respect to disease resistance. At crop level this concept is an old one. Under natural conditions different crop species were normally mixed, which helped to maintain a balance between host plants and pathogens. With the beginning of civilized cultivation, this interspecific diversification was reduced and the phase of intraspecific diversification started, during which farmers grew mixtures of different varieties of the same crop. The development of pure line varieties in the modem agricultural era considerably reduced this diversification at crop level and obliged breeders to seek disease-resistant characteristics through other breeding techniques.

The technique for the deliberate development of multiline varieties was first postulated by Dr. Norman E. Borlaug of the International Centre for the Improvement of Maize and Wheat (CIMMYT) in Mexico. Two multiline varieties, Miramar 63 and Miramar 65, were developed and released in Colombia to control yellow rust. However, as new semidwarf pure line varieties began to display their potential, not many efforts were made for the further development of multiline varieties.

The new multiline released in India, Kalyasona Multiline 3 (KSML 3), consists of six genetically different lines of wheat mixed mechanically in equal proportions. The six lines have the same agronomic characteristics, so that they are uniform in plant height, grain colour, grain type and maturity. But each line has different genetic background for resistance to yellow and brown rusts.

In tests conducted throughout the entire Northwestern Plains zone of India, which comprises the States of Punjab, Haryana, Delhi and parts of Uttar Pradesh and Rajasthan, KSML 3 outyielded Kalyasona by an average margin of about 9 percent. On the basis of its good yield performance, rust resistance and uniformity in plant type, it has been recommended for minikit trials on farmers' fields throughout the zone.