Protein, oil, and yield of soybean lines selected for increased protein

Soybean breeders need to evaluate alternative strategies for increasing yield, protein, and oil content. The correlated response for yield when selection is conducted for increased protein among unreplicated plant rows is unknown. Our objective was to evaluate selection for increased protein content at an intensity of 50% using unreplicated plots to determine the correlated response for yield, gross value per hectare, oil content, and the direct response for protein content. Ten populations that included 30 lines each were evaluated for yield, protein, and oil content at each of seven environments. Lines were selected solely for high protein content with one replicate at each of three selection environments and based on the average of two replicate in three selection environments. Additionally, selection was conducted on the basis of the population mean in the selection environment(s). Selected and unselected lines were evaluated in four validation environments that were not the same as the selection environments. Selection among individual lines solely for increased protein content decreased yield 70 kg ha^-1 and increased protein content 7 g kg^-1, when lines were selected on the basis of the mean of two replicates and three environments. Selection among populations for increased protein content, decreased yield 110 kg ha^-1 and increased protein content 5 g kg when selection was based on the population mean averaged across two replicates and three environments. On average, selection for increased protein content resulted in decreased yield.