GENETIC IMPROYEMENT OF SOYBEANS IN THE RIO GRANDE DO SUL STATE: I. GRAIN YIELD

Abstract

Experimento were carried out at the Seeds Research Center of Júlio de Castilhos (RS) from September of 1993 to May of 1994 to evaluate the progress in grain yield due to the soybean breeding programo in Rio Grande do Sul state, under three environmental conditions related to soil and crop management. The treatments included 21 soybean cultivars from different eras, chosen by their yield potential and their percentage of use by the soybean growers. The resulto show high progress in grain yield for the last 40 years.The genetic gain was 19 kg/ha/year or 1.1% per year, rangin g from 14.7 to 25.3 kg/ . ha annually, within every environment. When the cultivar 'Amarela Comum' was excluded the gain was 11.7 kg/ha/year, for a 30 years period. However, the grain yield gain hes been decreasing along the years probably because the soybean cultivars have reached high productivity levei and also because there has been constant use of the same germplasm bank for hybridization, creating a genetic narrow base. With emergente of new dioceses in the last decade, there were great changes on soybean varieties preferente, changing from varieties derived from Hill and Hood cultivars to genotypes originated from Davis cultivar. The changing was driven by resistancc to brown stem rot (Phialophora gregata). The great difference in grain yield among environments was due to better use of tecnology on soil and crop tillage.