Genetic diversity and disease control in rice

Crop heterogeneity is a possible solution to the vulnerability of monocultu red crops to disease(1-3). Both theory(4) and observation(2,3) indicate tha t genetic heterogeneity provides greater disease suppression when used over large areas, though experimental data are lacking. Here we report a unique cooperation among farmers, researchers and extension personnel in Yunnan P rovince, China-genetically diversified rice crops were planted in all the r ice fields in five townships in 1998 and ten townships in 1999. Control plo ts of monocultured crops allowed us to calculate the effect of diversity on the severity of rice blast, the major disease of rice(5). Disease-suscepti ble rice varieties planted in mixtures with resistant varieties had 89% gre ater yield and blast was 94% less severe than when they were grown in monoc ulture. The experiment was so successful that fungicidal sprays were no lon ger applied by the end of the two-year programme. Our results support the v iew that intraspecific crop diversification provides an ecological approach to disease control that can be highly effective over a large area and cont ribute to the sustainability of crop production.