Genetic improvement of barley yield potential and its physiological determinants in Argentina (1944-1998)

Barley breeding programs have empirically selected for improving grain yield and quality. The objective of this study was to quantify genetic gains in yield in 2-rowed malting barley cultivars released from 1944 to 1998 in Argentina, identifying the major physiological traits responsible for them. For this purpose, a field experiment was conducted in absence of biotic and abiotic stressful factors and with lodging being prevented mechanically. Until the 1970's, potential yield was maintained nearly constant at 5.25 mg ha(-1) and since then it increased at a rate of 41 kg ha(-1) year(-1). That bi-linear trend was closely related to the trend of averaged yields obtained by farmers. The contribution made by breeding yield potential to the total yield gains achieved by farmers was estimated in c. one third. Neither time to heading nor time to maturity were systematically modified by breeding. However, the partitioning of the developmental time was modified: time to achieve both maximum number of floret primordia and length of the jointing - heading period were increased with the year of release of the cultivars. The main component associated with yield was the number of grains per m(2), due to variations in number of spikes per m(2). Total and vegetative biomass at maturity increased with the year of release of the cultivars, at a rate of 45 and 19 kg ha(-1) year(-1), while both harvest index and stem height remained virtually unmodified. Differences in biomass at heading among cultivars were related to the improvement on the abilities to capture more radiation.