Screening For Genotypic Difference In N Use Efficiency And Identification Traits In Maize

The increase of nitrogen(N) is one of the main measure to raise the yield of maize. Excessive N application is not only to decrease the N utilization and to increase the cost of production, but also to cause groundwater polluted. In view of the situation, one positive and efficient method is breeding high N use efficiency(NUE) variety by the means of different genotypes in maize. Hybrids and inbred lines of typical maize were analyzed in different application N levels, and heritability of each character was studied for every generation of two high NUE cross combination in the experiment. The main results are as follows. 1 Based on NUE of maize under low and high application N conditions, hybrids and inbred lines could be preliminarily classified into four types, namely, double high efficiency which had high NUE at low and high fertilizer N, such as Nongda108, Jingzao15, HuangC and Dan330 et al., high efficiency in low N which had high NUE at low N, and NUE no change or slightly decrease in high N, such as Jingke132, Jingzao8, 340, 5003 and Zhong31 et al., high efficiency in high N which had low NUE in low N and high NUE in high N, such as Zhongdan9409, Jingken118, Zhingxia2, 00dong, Mo17 and 178 et al., double low efficiency which had low NUE in low and high N, such as Jingzao17, Zhongdan120, C8605, CA200, 107 and Yun146 et al.. 2 Response on N in different maize hybrids was analyzed. The results showed that significant difference existed among hybrids in grain yield, N accumulation, N efficiency and N responsiveness. The reaction character of maize hybrids to N was indicated according to N responsiveness. Path analysis revealed the direct effect of N uptake and N utilization contributed to NUE was bigger than indirect effect of that, and the N uptake efficiency was larger than the N utilization efficiency. The ear weight make considerable direct effects on grain weight per plant of maize. 3 The correlation level between yield and each properties at different application N was different. According to correlation analysis of yield and properties, the following traits should be included, higher chlorophyll content and big area of ear leaf at heading period, higher N content of grain, NUE and N harvest index in choosing cultivars at low N, and the big biomass at heading period and maturity should be included at high N. 4 Typical maize inbred lines were analyzed. The results showed that significant difference existed among inbred lines in yield, biomass, N accumulation amount and N responsiveness. Maize inbred lines can be classified into four types on the basis of NUE. Correlation among NUE and characters of inbred lines, yield and characters of inbred lines were analyzed. The resulted showed that in choosing inbred lines, the following traits should be included, higher chlorophyll content and big area of ear leaf at heading period, higher N content of grain and harvest index at low N, and the big biomass at heading period and maturity at high N. Path analysis showed that higher ear weight of inbred lines should be chosen in breeding high yield maize, the direct effect of N uptake and N utilization contributed to NUE was bigger than indirect effect of that. The direct effect of N uptake efficiency was bigger than the direct effect of N utilization efficiency at three application N and uptake was more effectively at low N. The direct of utilization to NUE was gradually strengthen along with increasing N fertilizer. 5 Analyses of correlation between NUE and N content of each part of plant showed that N content of leaf could calculate NUE at heading period and N content of grain at maturity and ear at heading period could predicate high and low for NUE at low N. Increasing N content of each part of plant was a prerequisite to raise NUE at high N about inbred lines. 6 Heritability and genetic progress of major characters in high NUE maize were studied. The results showed that the heritability of each maize traits was different at different N. The heritability of the chlorophyll content of ear leaf at heading period, NUE, ear weight and area of ear leaf were higher than other major characters at low N, the hereditary capacity of the biomass at heading period, ear weight, chlorophyll content of ear leaf at heading period and biomass at maturity were higher than other major characters at high N. These characters could be selected at early generation at low and high N, respectively. Under 5% selection strength, the different expected selection results of area of ear leaf, ear weight and chlorophyll content of ear leaf at heading period at low N, and of harvest index, biomass at maturity, grain weight in individual plant, NUE, yield of plot and ear weight at high N should be gained. Mid-parent and over-parent heterosis existed in F1 in related characters with high NUE. Selection for high NUE characters of high heterosis were extremely important in breeding inbred lines, it was beneficial to breeding high NUE maize hybrids. 7 Synthetic analysis showed that in choosing higher NUE hybrid and inbred lines at low N, the following traits should be included, higher chlorophyll content of ear leaf at heading period, big area of ear leaf, higher NUE and large ear weight. In choosing higher NUE hybrid and inbred lines at high N, the following traits should be included, big biomass at heading period, large ear weight and big biomass at maturity.