Associations among productivity, production response, and stability indexes in oat varieties

When three sets of 11, 15 and 31 varieties, respectively, were tested for grain yield in 5-23 environments, generally more than 80% of the yield variation for individual varieties was due to linear regression response. Mean yields for varieties were significantly variable in all three sets and regression response indexes were significantly variable in two of them. Mean yields over the three sets were correlated with regression response indexes (r = 0.61). Associations of mean yield with the stability parameters coefficient of determination, mean square for deviations from regression and ecovalence were low and usually not significant. The correlation of regression response indexes with coefficients of determination was r = 0.42, but neither of the other stability parameters was associated with the response indexes. The three stability parameters were closely correlated with one another. It is concluded from these results that an index R1, defined as the difference between the minimum and maximum yield of a variety in a series of environments, seems to provide a more accurate estimation of production response than does R2, defined as the difference between the yields of a variety in those environments giving the lowest and highest yields..