| Saline-alkali soil widely distributes across the world. Salinization and alkalization of soil is threatening the already-limited soil resource on which human being depends daily. Currently saline-alkali soil and secondary saline-alkali soil occupy the area of more than 40 million ha in China, and have become one of the main factors which limit agricultural development in this country. Maize is one of the main grain and feed dual-purpose crops, and one of the main crops grown on saline-alkali soil in Tianjin. In order to increase the maize production on saline-alkali soil, studies, such as clarifying physiological mechanism of haloduric maize, identification of salt tolerance for different varieties, are of great importance. In this study, responses of maize to NaCl solutions in germination stage and seedling stage were investigated. Inbred lines and hybrids showing salt tolerant and the salt sensitive phenotypes respectivly were screened and identified. And maize metabolism in physiological and biochemistry level was studied in detail. Then combining abilities of salt-tolerant maizes in eight yield traits were analyzed. The results from this study show as follows.1 To screen salt-tolerant and salt-sensitive maize varieties, 225 inbred lines and 21 hybrids were treated with 2‰and 7‰NaCl respectively, and classified according to measurements on seedling height, seedling fresh weight, relative water content (RWC) of seedling and root, root length, root fresh weight and seed germination power. Five maize inbred lines (A691Ht, D80-366, Longyu113(♂), 07-115, 21836) were graded as"salt tolerant"and other five inbred lines (B73,D141-261,D158-20,D153-70,D49-253) as"salt sensitive".2 The germinability, seedling height and root viability of all maize varieties reduced under salt stress. The seedlings of Zhengdan 958, Tianta3, Tianta5 were higher than those of Jiyuan1, Danyu92 and Qidan1 when challenged with 10‰NaCl. Salt -sensitive varieties showed lower root viability compared to that of salt-tolerant varieties. Relative Electric Conductivity (REC) of maize increased accompanying with enhanced salt stress, and REC of salt sensitive maize increased faster than salt tolerant ones 15 days after after salt treatment.3 The antioxidant enzymes of six varieties showed different activity under salt stress. The SOD activity increased following elevated NaCl in a range of concentrations (0-8‰for salt-tolerant varieties and 0-6‰for salt-sensitive ones), then decrease dramatically with elevated NaCl concentration. Salt-tolerant varieties could remain high POD activity under salt stress.The content of MDA, proline and soluble proteins increased after application of NaCl. Salt-sensitive varieties produced more MDA under enhanced salt stress compared to that of salt-tolerant varieties. The content of proline decreased while salt stress prolonged. Proline content start to increase 7-13 days after salt stress and to decrease significantly from the 15th day. Salt-tolerant varieties created more proline and soluble proteins facing salt stress.4 Na+ content of six varieties increased in roots, shoots and leaves, and Na+ content in roots was much higher compared to shoots and leaves under salt stress. But the contents of K+, Ca2+ and the ratios of K+/Na+ and Na+/Ca2+ decreased with salt treatment. Under severe salt stress,K+ content of salt-tolerant varieties decreased dramatically in roots, while K+ content of salt-tolerant varieties in shoots was lower than those of salt-sensitive varieties. K+ content of shoots and leaves was far higher than that of the roots from the same plant. Ca2+ content of shoots and leaves in salt-tolerant varieties reduced slower than salt-sensitive varieties. Salt-resistant varieties maintenanced high ratio of K+/Na+ in shoots and leaves, while salt-sensitive varieties did the same in roots. The ratio of Na+/Ca2+ in shoots and leaves of salt-sensitive varieties droped much faster than that that of salt-sensitive varieties under severe salt stress.5 The content of chlorophyll a, b, and carotenoids declined under salt stress. With prolonged treatment, chlorophyll a, b, and carotenoids of salt-tolerant varieties accumulated gradually, but those of salt-sensitive varieties did reversely.6 The genetic analysis of yield traits in salt-tolerant maize indicated that there were significantly differences among combinations, female parents, and the interactions of parents. General combination ability (GCA) of ear grain weight listed in descending order: D141-261, D153-70, D80-366, D21836, A691Ht, and D158-20, and the combinations with high SCA were A691Ht×21836, D141-261×D158-20, D80-366×D49-253, B73×D49-253, Long yu 113(♂)×07-115 and B73×21836. Inbred lines with superior traits, D141-261 and D80-366, were determined through comprehensive analysis of the GCA and SCA. The broad-sense heritability of yield traits listed in descending order: ear diameter, ear length, ear grain weight, plant height, ear height, 100-kernel weight, kernel number per row, and row number of ear. The narrow-sense heritability of yield traits listed as follows: ear grain weight, ear length, plant height, ear diameter, ear length, row number of ear, 100-kernel weight, and kernel number per row.
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