Diffusion patterns of individual rice varieties in Colombia and Southern Brazil

Planting a limited number of varieties over a wide area is a cause for concern, as sudden susceptibility to pest and disease may lead to crop catastrophes. The approach to broaden genetic diversity on farms is to make available various gene sources and exploit specific environmental adaptation through frequent varietal releases. This paper describes the diffusion patterns of nine irrigated-rice varieties released druing 1971-81 in Colombia and Southern Brazil, to guide efforts to increase varietal alternatives on farms. A three-phased, segmented regression model was found appropriate to describe the observed patterns in share of area planted to individual varieties. The cycle started with a parabolic phase, followed by stability and ended with a period of decrease. Five of the six Colombian varieties released between 1971 and 1981 completed the diffusion cycle, while all three released in Brazil in 1971 and 1978 only reached the stability phase. The general pattern suggested an early interest in new varieties followed by the identification of the niches under which commercial potential was maximized. The final stage indicated that improved varieties with similar adaptation became available. The observed dynamism in varietal use could be maintained with the commercial exploitation of a new germplasm base eng