[Changes of grain yield and agronomic traits during millet variety replacements in northern Shaanxi, China.]

A field trial was conducted to examine the differences of grain yield and agronomic characters of six millet ( Setaria italica ) varieties in Yulin, Shaanxi during 2018-2019 growing seasons. Those varieties were planted in northern Shaanxi in different decades (1960s-1970s, 1980s-1990s, 2000s-2010s). The results showed that the grain yield of millet varieties exhibited an increasing trend across all the decades. The average yield of varieties bred from 2000s to 2010s were 0.46 (2018) and 0.66 kg·m ^-2 (2019), respectively. The yield increased significantly by 22%-53% compared with the bred before 2000s. Changes of plant height, panicle weight, leaf weight and stem weight were similar to that of yield, while one-thousand kernel weight and spike length were relatively stable which did not change significantly across the decades. The flag leaf width increased significantly with the variety replacements. There was a significant correlation between panicle weight, stem weight, leaf weight, plant height and grain yield, respectively. Results of principal component analysis showed that millet varieties bred from 2000s to 2010s had greater advantages. In the process of millet cultivars replacement in northern Shaanxi, yield per unit area was mainly increased through the improvement of plant height and spike weight. In the future, we should focus on the improvement of plant height, spike weight, stem weight, and leaf weight, especially the exploration of the optimal plant height suitable for mechanical harvesting.