| Maize (Zea mays L.) is a global food security crop that is grown widely throughout the world in a range of agro-ecological environments. As the consequences of global warming and climatic change, salinity affects the world food production. Improving salt tolerance in crops is an important target for plant breeding in the near future. However, salinity tolerance is not easy to breed for as it interacts in plants with many physiological processes that are controlled by many genes and that are influenced by environmental factors. Besides an important crop, maize is also an excellent experimental model species for genetic studies. Maize is one of the most salt-sensitive field crops, showing obvious signs of stress but there is evidence that considerable intra-specific genetic variation for salt tolerance exists in maize. The present studies apply genetic and experimental breeding approaches to reveal the genetic and physiological mechanisms underlying natural variation for salt tolerance in maize and to find ways to explore this variation. The aim is to genetic improvement of salt tolerance in cereal crops through marker-assisted selection.Nine maize genotypes were evaluated under salt stress at germination and seedling stage. These maize genotypes were screened in a hydroponics system comparing with a newly developed vermiculite-culture method to identify heritable variation for salt tolerance traits and suitable screening method for genetic analysis of salt tolerance. The different genotypes significantly differ in their salt tolerance with respect to seed germination and seedling growth. Among the genotypes under investigation inbred line CZ-7expressed as the tolerant genotype and B73appeared to be more sensitive at germination stage. Significant variations were observed in all physiological attributes and ionic contents at seedling stage. The maize inbred line CZ-7had higher plant growth, higher K+/Na+ratio and found more salt tolerance at all salinity levels. While maize inbred line B73had lower plant growth, lower K+/Na+ratio as compared to all other maize genotypes and was considered as salt sensitive genotype. The results having good reproducibility among two screening methods authenticated the validity of the vermiculite-culture method for the assessment of salinity at early stage of plant growth in maize.In order to discover the inherent basis for salinity tolerance traits in maize,121polymorphic simple sequence repeat marker (SSR) markers were used to analyze163F2individuals derived from a single cross of inbred line B73(a salt susceptible inbred line) and CZ-7(a salt tolerant inbred line). A linkage map was constructed and the map covered1195.2cM of maize genome with an average distance of9.88cM between marker loci. Ten salt tolerance traits at seedling stage were evaluated for QTL analysis in maize seedlings. A total of41quantitative trait loci (QTL), including shoot length (SL), root length (RL), ratio of root length and shoot length (RRLSL), shoot fresh weight (SFW), root fresh weight (RFW), plant fresh weight (PFW), shoot dry weight (SDW), root dry weight (RDW), plant dry weight (PDW) and ratio of root dry weight and shoot dry weight (RRDWSDW), were detected, with16and25QTLs under non-salinity and salinity condition, respectively. And4major stable QTLs were detected in two environments. The detected QTLs were distributed on chromosomes1,2,4,5,6,7,8,9and chromosome10. Phenotypic variability for the identified QTLs for all the traits was in the range from6.27to21.97%. Fourteen QTLs with more than10%contributions were observed. Our results and the markers associated with the major QTL detected in this study have the potential application for genetic improvement of salt tolerance in maize through marker-assisted selection. |
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