Evaluation of Genetic Diversity of Maize Lines (Zea mays L.) under Normal and Salinity Stress Conditions

Maize, or corn, as one of the staple food products and forage crop, in addition to having a high grain and biomass yield, is of particular importance in the supply of carbohydrates, edible oils, and renewable energy. The plant is grown under a wide range of climatic conditions and is relatively sensitive to salinity. The development of salt-tolerant varieties of plants is inevitable policy in response to the growing demand for food in sustainable agriculture system. In the present study, the genetic diversity of 86 maize lines was investigated using morphological traits in a randomized complete block design (RCBD) with three replications under normal and NaCl salinity stress (EC 8 dS/m) in potted conditions. The results showed that salinity stress led to a significant decrease in mean of grain yield (GY), flag leaf length (FLL), flag leaf width (FLW), flag leaf area (FLA), ear height (EH), leaf angle (LA), stem diameter (SD), potassium to sodium ratio (K/Na), relative leaf water content (RWC), and number of rows per ear (RPE). In contrast, salinity stress caused a significant increase in the mean of days to tasseling (DTT) and days to silking (DTS) compared to normal conditions. Grain yield showed a very high positive correlation with biomass yield (BY), number of grains per row (GPR), ear length (EL), ear diameter (ED), grain depth (GDE), and cob weight (CD) under both normal and salinity stress conditions. The results obtained from stepwise regression analysis using Mallows’ Cp, and path analysis showed that, traits include number of grains per row (GPR), hundred grain weight (HGW), grain width (GW), and total leaves (TL) under normal conditions and traits include number of grains per row (GPR), grain depth (GDE), cob weight (CD), and ear diameter (ED) under salinity stress conditions were the most important traits affecting grain yield (GY). The great amount of h2 communality of mentioned traits in factor analysis was in order to confirm these results. According to the results of factor analysis using parallel analysis and very simple structure criterion (VSS), four hidden factors were determined in both normal and salinity stress conditions, which explained 60% and 65% of the variability among the maize lines, respectively. Before conducting the cluster analysis, three clusters were determined as the optimal number of clusters by elbow, silhouette and Gap statistics methods in each of normal and salinity stress conditions. Then, hierarchical cluster analysis of the studied maize lines was performed based on measured traits using Ward’s minimum variance method. Therefore, in case of need for hybridization to achieve salt-tolerant maize hybrids and improvement of important agronomic traits, suitable parents can be selected from the first and third clusters using comparisons of mean of the traits in clusters under salinity stress conditions and also with the help of the biplot obtained from principal component analysis (PCA). Targeted crossbreeding between selected parental lines allows for further exploitation of phenomena such as heterosis and aggressive segregation.