PRODUCTIVITY AND ADAPTIVE CAPACITY OF WINTER-WHEAT LANDRACES AND MODERN CULTIVARS GROWN UNDER LOW-FERTILITY CONDITIONS

In recent decades, most winter wheat (Triticum aestivum L.) breeding i n the United States has been done in field nurseries in which the soil receives ample fertilization. To determine the effects of these breed ing efforts on productivity under low-fertility conditions, we evaluat ed twenty-nine winter wheat genotypes (seven Asian landraces; thirteen standard-height US. cultivars released between 1874 and 1971; and nin e semidwarf cultivars released between 1977 and 1988) under severe fer tility stress at three Kansas, USA locations. Experiments included fer tilized and unfertilized treatments. The modern, semidwarf cultivars y ielded 18% and 20% more, on average, than landraces and standard-heigh t cultivars under low and high fertility, respectively; however, only the latter difference reached the 5% significance level. At only one l ocation (Hays) was there a significant genotype X fertility interactio n: there, 89% of the semidwarf cultivars, only 8% of the standard cult ivars, and 57% of the landraces responded to fertilization. The regres sion coefficient of mean grain yield (unfertilized) on year of introdu ction or release for standard and semidwarf cultivars was zero, indica ting that a century of breeding has produced no genetic improvement in performance under these low-fertility conditions. Although we found t hat the usual yield advantage of modern cultivars is not expressed und er very low fertility, we saw no evidence that older cultivars are sup erior under those conditions.