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 cro p catastrophes. The approach to broaden genetic diversity on farms is to make available various gene sources and exploit specific environmen tal adaptation through frequent varietal releases. This paper describe s the diffusion patterns of nine irrigated-rice varieties released dur ing 1971-81 in Colombia and Southern Brazil, to guide efforts to incre ase varietal alternatives on farms. A three-phased segmented regressio n model was found appropriate to describe the observed patterns in sha ve of area planted to individual varieties. The cycle started with a p arabolic phase, followed by stability and ended with a period of decre ase. Five of the six Colombian varieties released between 1971 and 198 1 completed the diffusion cycle, while all three released in Brazil in 1971 and 1978 only reached the stability phase. The general pattern s uggested an early interest in new varieties followed by the identifica tion of the niches under which commercial potential was maximized. The Fnal stage indicated that improved varieties with similar adaptation became available. The observed dynamism in varietal use could be maint ained with the commercial exploitation of a new germplasm base.