Research progress on the mechanisms and nutrient efficiency indicators for minor cereal crops of the Poaceae family

There are large area of medium- and low-yield farmlands in China, nutrient deficiency has been a key factor limiting crop production in these areas. Foxtail millet, proso millet and sorghum are the traditional minor cereal crops in China, having the properties of higher photosynthetic efficiency, drought and barren tolerance. They are more suitable to drought and nutrient deficient conditions than the main staple crops like wheat, rice, and maize. However, researches on nutrient efficiency mainly focuses on staple crops, fewer on minor cereal crops. In this paper, we systematically summarized the researches about the efficient utilization of N, P, and K in foxtail millet, proso millet and sorghum, and the screened indicators for nutrient efficiency in these minor cereal crops. The reported morphological indicators include above ground dry weight, panicle diameter, panicle weight, grass weight, yield, et al. Physiological indicators include nitrogen assimilation enzyme activity, phosphorus accumulation, photosynthetic nutrient use efficiency, etc. The main indicators for nutrient absorption efficiency include root size, root length, lateral root branching, and root diameter, as well as candidate genes, which may be involved in nutrient efficiency, NRT1, PHR1, potassium transporter HAK, and potassium channel protein Shaker. In the future, more researches should be carried out on the characteristics of high photosynthetic efficiency and drought and sterility tolerance of root systems in minor cereal crops; the interspecific and intraspecific variations of photosynthetic nutrient efficiency using transcriptomic methods, especially the mechanisms caused by nitrogen and phosphorus component variations in plants; the root morphology traits and the derivative root-microbial interactions on the nutrient absorption efficiency of minor cereal crops. These research results will provide theoretical guidance for the cultivation of nutrient-efficient grain cultivars and efficient cultivation techniques.