Rank comparisons of maize germplasm evaluations repeated over locations and years

Summary

The availability of yield and combining ability data on germplasm bank accessions may increase their use, but collection of this type of data from a large number of accessions is difficult and expensive. This study was conducted to determine whether the members of the top 20% of evaluated accessions changed so extensively, when evaluations were repeated over locations and years, that initial evaluations conducted in one location were misleading. Thirty-four Yugoslavian maize (Zea mays L.) accessions were evaluated for yield per se and as test crosses to eight testers in three Iowa locations during three years. Overall “best” accessions were assumed to be those that performed best, as judged by all of the data. The highest yields occurred in Kanawha, Iowa, in 1987, which had favorable climatic conditions for maize production, whereas the lowest were in Kanawha in 1985, which had the least desirable conditions. In these two years, however, one testcross evaluation placed more of the actual overall best accessions in the top 20% of the highest yielding accessions for that particular evaluation. More “overall best” were ranked in the top 20% in the year with less desirable conditions. The efficiency of an environment in ranking the best accessions in the top 20%, while excluding the worst 20%, ranged from 16% in Nashua, Iowa, in 1985 to 48% in Nashua in 1986. Repeating evaluation trials over years was no more efficient than repeating them over locations, or vice versa. Initial germplasm evaluations should be repeated either over locations or years, to increase the probability of identifying the rare agronomically valuable accessions and eliminating poorer-yielding ones.