To screen the desired criterion to identify desirable genotypes and select genotypes best suited to limited nitrogen availability in order to facilitate the practice of low-nitrogen-tolerant breeding in maize, the response of 31 maize inbred lines, containing four control inbred lines (PH6WC, PH4CV, Zheng58, and Chang7-2) and others selected from the Shaan A and Shaan B heterotic groups cultivated at Northwest A&F University (Yangling, Shaanxi, China), were evaluated. The experiment was conducted following a split plot design with two replications during three growing seasons (2015, 2016, and 2017) under both high nitrogen (HN) and low nitrogen (LN) conditions at the Yulin and Yangling in Shaanxi Province, China. Seven screening indices, based on grain yield under two contrasting nitrogen (N) conditions, the stress susceptibility index (SSI), yield stability index (YSI), mean productivity (MP), geometric mean productivity (GMP), stress tolerance index (STI), harmonic mean (HM), and low nitrogen tolerance index (LNTI), were computed to assess the overall index that accurately screened the desirable genotypes. The results of the correlation analyses and principal component analysis showed that MP, GMP, HM and STI were correlated with grain yield significantly and positively under contrasting N conditions, and were able to accurately discriminate the desirable genotypes. Compared with the control inbred lines, many inbred lines selected from the Shaan A and Shaan B groups showed a higher LN tolerance. This shows that we can effectively improve the LN tolerance of maize inbred lines through LN screening. Based on the screening indices, the three-dimensional diagram and genotype and genotype × environment (GGE) biplots are agreed with this results, and we identified KA105, KB081, KA225, 91227, and 2013KB-47 as the desired genotypes that have the potential to be used to breed a high yield and stable hybrid.

Maize (Zea mays L.) leaf is the main organ for photosynthesis. The area of leaves (especially the ear-leaf and the two leaves above and below the ear-leaf) plays a vital role in dry matter accumulation and grain yield. Therefore, genetic information on leaf area has a theoretical significance for breeding maize with high yield. In this study, a genetic linkage map composing of 184 simple sequence repeat (SSR) markers was constructed based on an F8 recombinant inbred line (RIL) population, which was derived from a cross between 478 and W312. The parents showed a significant difference in leaf area. The map covers 2084.1 cM with an average interval of 11.3 cM. QTLs for leaf area were identified under two-year's field experiments. Totally 7 QTLs were detected in two years, among which 4 QTLs were detected in 2006 and 3 QTLs in 2007. A major QTL on chromosome 2 (between umc1542 and umc1518) were detected in both 2006 and 2007. It explains 12.5% and 17.3% of the phenotypic variation, respectively. This locus can be used as a potental marker for improving maize leaf growth through marker assisted selection (MAS) approach.