GENETIC PROGRESS IN WINTER WHEAT CULTIVARS RELEASED IN CHILE FROM 1920 TO 2000

Wheat ( Triticum aestivum L.) is the major crop in terms of planted area and presents the largest distribution in the country covering a wide range of climatic regions. This study assesses the changes of various agronomic traits of winter wheat cultivars released in Chile between 1920 and 2000. A total of 117 winter accessions, representing 45 old and 72 modern cultivars were tested in a humid Mediterranean-type climate, with irrigation, in 2003. Old cultivars were those released before 1960 and modern ones were those released after 1960. Principal component (PC) analysis using 10 agronomic traits clearly separate modern from old cultivars of winter wheat. Comparing modern cultivars with old ones, plant height have been reduced by 25.6%, but others traits have increased, like harvest index (21.1%), number of grains per ear (42.6%), sedimentation value (103%), and grain hardness (32.0%). The variation in plant height was negatively correlated with harvest index (r = -0.30, p < 0.001). Grain yield, a trait not included in PC analysis, was highly correlated with the second PC (r = 0.81, p < 0.0001). Significant (p < 0.01) correlations were found between the year of release of cultivars and agronomic traits: plant height (r = -0.82), harvest index (r = 0.40), number of grain per ear (r = 0.69), sedimentation value (r = 0.64), and kernel weight (r = -0.46). Those correlations were mostly a consequence of absence or presence of dwarfing genes in the germplasm. Finally, the yield progress was calculated from yield data of yield trial with 15-25 cultivars and advanced lines of winter wheat tested almost every year from 1965 to 2001, showed no increase in yield between 1965 and 1975, but an increment of 246 kg ha-1 per year between 1976 and 1998, representing an annual increase of 2.6%