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STATISTICS

A Statistical Method for Summarizing Results of Cultivar Performance Trials

Dep. of Agron., Kansas State Univ., Manhattan, KS 66506

^* Corresponding author (amfeyer{at}ksu.edu).

Received for publication March 24, 2003. Cultivars in yield trials are normally compared by means and ranks, but extrapolating results to the future is difficult because good estimates of variances are lacking. The purpose of this research was to construct and apply a statistical method capable of producing probabilistic inferences about future yielding ability from a sample of cultivar performance trials (CPTs). Our database was CPTs of fall- and spring-planted wheat (Triticum aestivum L.) in the U.S. Great Plains. The mean yield of selected check cultivars that were common to a set of trials established the standard level of performance for each trial in that set. Differences in yields between other cultivars and the trial standard provided the differential yielding ability (DYA) values for those cultivars in that trial. Cultivars were judged by their performance in relation to check cultivars in a sample composed of trials from multiple locations over multiple seasons within an ecogeographic region. We assumed that environmental effects were random from trial to trial and DYA values were normally and independently distributed. This led to use of Student's t distribution for probabilistic inference about population mean DYA values. We applied our method to elite trials in several regions in our database. For each cultivar, we showed its mean DYA, standard error, and p value when testing the null hypothesis. The method can be applied to advancing generations of experimental lines in breeding trials as well as recommending late generations for release as new cultivars.

Abbreviations: CPT, cultivar performance trial • df, degrees of freedom • DYA, differential yielding ability • SE, standard error