Abstract:

Millet is an important food crop grown in arid and semi-arid regions of northwest China and has high nutritional value. However, in recent years, frequent droughts have led to the degradation of millet varieties and the decline of quality. Because the root system is an important organ to transport organic matter and is critical to the whole process of plant growth and development, six varieties of millet of three different decades were selected as the research objects, and the soil culture method was used to simulate the drought environment (10 days after emergence, one group stopped watering until harvest, another group was irrigated normally, 70%±5% FWC) to explore the mechanism of drought stress on millet seedling root phenotype in the process of variety replacement. The results showed that the response mechanism of millet seedling roots to drought stress was different in varieties of different decades. With the advance of the variety replacement, the root dry mass, root length, root surface area and root volume of millet seedlings decreased first and then increased. The growth rate of millet in drought environment increased by 18.1% and 30.1% in 1970s—1980s varieties and 2000s—2010s varieties, respectively (P<0.05). The root-shoot ratio tended to decrease and stabilized at about 0.21, and the number of roots stabilized at 9-10. Under drought stress, the total dry biomass, root width, total root length, root surface area and root volume of the 1960s—1970s varieties decreased significantly by 37.6%, 47.9%, 36.8%, 40.1% and 30.6% (P<0.05) respectively, while the root density had no significant difference (P>0.05). For varieties of 1970s—1980s, the total dry mass, root width and root number increased by 59.8%, 21.4% and 27% (P<0.05), respectively, while the root surface area, root volume and total root length had no significant difference (P>0.05). For varieties of 2000s—2010s, the root width, total root length and ratio of root length decreased significantly by 28.5%, 15.3% and 35.9% (P<0.05), while the root surface area, root volume and specific root length had no significant difference (P>0.05). The results of this study showed that under drought stress, the root sensitivity of modern millet varieties at seedling stage decreased, the phenotypic difference was narrowed, and the tolerance was improved.

Key words: millet, drought stress, variety replacement, root phenotype