Nitrogen allocation and remobilization contributing to low-nitrogen tolerance in stay-green maize

Nitrogen (N) efficient cultivars can achieve relatively high grain yield under reduced N input. Normally modern stay-green maize cultivars are high-yielding and more N efficient than the old senescent cultivars. However, less is known about the genotypic difference in N use efficiency (NUE) among stay-green high-yielding cultivars. This information is crucial for further genetic improvement in NUE of the modern stay-green cultivars. In the present study, two stay-green hybrids with different NUE, Zhengdan958 (ZD958, N-efficient) and Liangyu99 (LY99, Ninefficient), were grown under 60 (LN) and 180 kg N ha-1 (HN) conditions in a 4-year field experiment with split-design. The two hybrids did not differ in grain yield under HN. Under LN, grain yield and grain N content of LY99 was 23.6 % and 30.3 % lower compared to that of ZD958, respectively. LY99 had few grain number per row than ZD958. Correspondingly, floret primordia number decreased by 17.7 %, and grain abortion increased by 12.7 % in LY99 compared to ZD958. During critical period around silking, N concentration in the young ear of LY99 is lower than that in ZD958. Also, the maximum absolute ear growth rate and exponential duration of LY99 were 22.2 % and 6.0 % lower than that of ZD958 under LN, respectively. In LN conditions, the two hybrids did not differ in post-silking N accumulation. However, N remobilization from vegetative organs to grains in LY99 was 41.3 % lower than that in ZD935. In conclusion, NUE in stay-green cultivars could be improved by efficient N allocation into the young ear and vegetative-N remobilization during post-silking period under insufficient N supply.