Effect of nitrogen rate on matter production and nitrogen metabolism traits of cytoplasmic male sterility maize (Zea mays L.)

Cytoplasmic male sterility (CMS) plays an important role in maize (Zea mays L.) breeding for increasing yield and reducing costs. To investigate the effects of nitrogen rates after anthesis on carbon and nitrogen metabolism traits, we conducted a pool experiment by two nitrogen treatment in 2004–2005 with two inbred lines, cytoplasmic male sterility (478CMS and Qi319CMS) and homotype fertile lines(478 and Qi319). The result showed that compared with their homotype lines (the maintainer lines), CMS lines had higher grain yield and harvest index under two nitrogen levels (P0.05), no significant difference existed in above-ground dry weight (P0.05), maintained larger root amount and higher root/shoot ratio at nitrogen deficiency. (P0.05). CMS lines had green-maintaining character and higher net assimilation rate, photosynthetic rate (Pn) of ear leave at late growth stage. Also, CMS lines maintained higher nitrate reductase (NR), glutamate synthetase（GS）and glutamate dehydrogennase（GDH）activities of ear leaf under two nitrogen levels (P0.05). The nitrogen content and nitrogen assimilation amount of leave, stalk and root of CMS lines showed great advantages at former stage(0-20 d) after anthesis, whereas uptake and accumulation ability were not strong at late growth stage, but CMS lines had higher nitrogen translocation rate, nitrogen contribution rate and nitrogen utilization rate than those of their homotype lines, especially at nitrogen deficiency. These suggested that CMS lines had strong photosynthetic carbon production and nitrogen metabolization, improved nitrogen translocation and uitilization efficiency, thus, increased the grain filling ability and yields.