Abstract: Male sterility of higher plant is a common phenomena found in many species. Cytoplasmic male sterility (CMS) plays an important role in maize (Zea mays L.) breeding for its advantages of yield and reducing costs. It is reported that CMS maize has a positive effect on yield of single and double hybrids, as well as their homotype hybrids. Normal detasseling and CMS hybrid probably lead to higher yield under stresses, and the increase extent of yield varies with stress degree. Most grain yields of CMS lines are higher than those of their homotype lines, and male sterile plants have different effects with different genotypes. Plant photosynthesis traits have a direct influence to yield. However, the mechanism of increasing yield by male sterility is uncertain. To investigate the effects of low nitrogen after anthesis on grain yield and photosynthetic traits, we conducted a field experiment by low nitrogen treatment in 2004–2005 with two inbred lines, cytoplasmic male sterility (478CMS and Q319CMS) and homotype fertile lines(478 and Q319). The fertilizer was applied at one time before sowing, we sampled at 0, 10, 20, 30, 40 d after anthesis to determine the nitrogen content and the photosynthesis traits at the same time. Grain yield and yield components were measured after maturity. The result showed that compared with their homotype lines (the maintainer lines), CMS lines had higher grain yield with the increase by 11.5%, significantly greater kernel weight and harvest index, but no significant difference in numbers of kernels per panicle. Also, CMS lines maintained higher nitrogen, chlorophyll and soluble protein contents, and larger leaf area index at late growth stage, indicating that CMS maize has a better green-maintaining character, prolonging effective photosynthesis duration and postponing the senescence course of plant. In CMS lines, photosynthetic rate (P_n), intercellular CO₂ concentration (C_i) and stomatal conductance (G_s) were higher at late growth stage obviously, and not sensitive to nitrogen deficiency in soil. Chlorophyll fluorescence parameters such as the actual photochemical efficiency (FPSⅡ), the apparent electron transfer rate (ETR) and the maximal photochemical efficiency (F_v/F_m) of CMS lines were higher than those of their homotype lines. These suggested that CMS lines have great advantages in photosynthesis ability, electron transfer, and light energy transform at late growth stage, and the higher grain yield of CMS lines comes from the common improvement of leaf physiological activity and photosynthetic efficiency in grain filling period.

Key words: Maize, Cytoplasmic male sterility (CMS), Yield, Nitrogen deficiency, Photosynthetic characteristics