A SUPERIORITY MEASURE OF CULTIVAR PERFORMANCE FOR CULTIVAR × LOCATION DATA

Abstract

A measure of cultivar general superiority for cultivar × location data is defined as the distance mean square between the cultivar’s response and the maximum response averaged over all locations. Since the maximum response is the upper boundary in each location, a small mean square indicates general superiority of the test cultivar. The method requires that all test cultivars be balanced over locations but not necessarily the checks. The advantage of the proposed method are: (i) The checks provide only a plausible maximum response for each location and are not required for assessing the test cultivars. Thus checks do not have to be present in all locations. This allows a greater flexibility for a breeder to choose locally adapted cultivars as checks without unduly increasing the size of a regional trial. (ii) The measure of general superiority consists of only one parameter, thus simplifying the screening process considerably. A subsidiary parameter for interaction can be used to indicate lack of general adaptability. (iii) The difference between the mean of the maximum response averaged over all locations and the mean of the best cultivar provides useful information as to how many cultivars are needed to achieve optimum productivity for the entire region, (iv) The specific adaptability of a cultivar can be identified by plotting the maximum and the test cultivar responses on the location means.Key words: Genotype × environment interaction, cultivar assessment, regional trial