WHEAT RUSTS AND THE COST OF GENETIC DIVERSITY IN THE PUNJAB OF PAKISTAN

The theory of impure public goods is used to demonstrate why farmers m ay nor grow wheat cultivars with the socially desirable level of rust resistance. First, they may grow cultivars that are high yielding thou gh susceptible to rust. Second, many farmers may grow cultivars with a similar generic basis of resistance. Expected rust losses can be redu ced by (a) more diversified genetic background in released wheat culti vars; (b) greater spatial diversity in planted cultivars; or (c) use o f a temporally changing fist of cultivars known to be rust resistant, Yield trade-offs associated with these policies illustrate potential f asts of increasing genetic diversity.