Document Type : Original Article

Authors

• Maryam Harati Rad ¹
• Nafiseh Mahdinezhad ²
• Reza Darvishzadeh
• Baratali Fakheri ³
• Mitra Jabari ⁴
• Sorour Arzangh ⁵

¹ PhD student of Plant Breeding, Department of Plant Breeding and Biotechnology, Faculty of Agriculture, University of Zabol, Sistan and Baluchestan, Iran

² Associated Professor, Department of Plant Breeding and Biotechnology, Faculty of Agriculture, University of Zabol, Sistan and Baluchestan, Iran

³ Professor, Department of Plant Breeding and Biotechnology, Faculty of Agriculture, University of Zabol, Sistan and Baluchestan, Iran

⁴ Assistant Professor, Department of Plant Production and Genetic Engineering, Faculty of Agriculture, University of Saravan. Sistan and Baluchestan, Iran

⁵ Ph.D., Department of Plant Production and Genetics, Faculty of Agriculture, Urmia University,Western Azerbaijan, Iran

Abstract

Introduction
Maize, like other plants, faces various environmental constraints during its growth period, such as the lack of nutrients. In calcareous soils, zinc deficiency reduces growth and yields. One of the important methods for improving tolerance to environmental stresses is the study of plant genotypes under stress conditions. In order to distinguish genotypes tolerant to stressful conditions, several tolerance indices are used. Genotypes are divided into 4 groups based on their reactions to normal and stressful environmental conditions. Group A includes genotypes that show good performance in both stress and normal conditions. Group B includes genotypes that show good performance only in stress-free environment. Group C includes genotypes that show good performance only in stressful environment and group D includes genotypes that show low performance in both stress and normal conditions. This experiment was carried out with the aim of evaluating the tolerance of maize genotypes to zinc deficiency by using stress tolerance indices.
 
Materials and methods
Ninety-three maize genotypes were evaluated morphologically under optimal and zinc deficiency conditions using alpha lattice design with two replications in field conditions at Zabol Agriculture and Natural Resources Research Center, during 2 successive crop years (2020 and 2021). Based on the grain yield of maize genotypes under optimal and zinc deficiency conditions, 10 stress tolerance indices including tolerance index (TOL), mean productivity index (MP), geometric mean productivity index (GMP), stress tolerance index (STI) , abiotic tolerance index (ATI), stress sensitivity index (SSI), drought stress resistance index (DI), harmonic mean (HM), modified stress tolerance index (MPSTI), and modified stress tolerance index in moderate and severe stress (MSSTI) were calculated. Pearson's and partial correlations between indices were calculated using corrplot package in R and SPSS version 26 softwares. A three-dimensional diagram was drawn to identify genotypes tolerant to zinc deficiency with high yield in both normal and zinc deficiency conditions using Statistica version 10 software, in which the grain yield under stress conditions was considered on the X axis, grain yield in optimal conditions was considered on the Y axis and one of the selected indices was considered on the Z axis. Principal components analysis and hierarchical clustering using Ward's method on standardized data were done using the factoextra and Cluster packages in R software, respectively.
 
Results and discussion
Based on the results of analysis of variance, statistically significant difference was observed among the studied maize genotypes in terms of grain yield under optimal and zinc deficiency conditions, as well as all calculated stress tolerance indices. The t-test showed statistically significant difference between the average seed yield of the genotypes in optimal (77.85 g pl^-1) and zinc deficiency onditions (61.86 g pl^-1). Grain yield in optimal conditions showed a positive and significant correlation with all indices except DI index. The highest correlation was related to MP, MpSTI, GMP, STI, ATI and HM indices. Grain yield under zinc deficiency conditions showed a negative and significant correlation with SSI (-0.45), TOL (-0.41) and ATI (-0.28) indices. Other indices showed a positive and significant correlation with grain yield under zinc deficiency conditions. The positive and significant correlation of GMP, MP, STI and HM indices with grain yield in both optimal and zinc deficiency conditions indicates that these indices are the best and most appropriate indices to identify and select maize genotypes tolerant to deficiency stress. Principal component analysis showed that the first two components explained about 95.42% of total variations. Cluster analysis classified maize genotypes into 5 groups comprising 27, 9, 23, 17 and 17 genotypes per each group, respectively. The genotypes classified in group 4, 2 and 1 were identified as highly tolerant (stable), tolerant and sensitive to Zn deficiency stress, respectively.
 
Conclusion
High genetic diversity was obtained between the studied genotypes in terms of grain yield and stress tolerance indices. Using the three-dimensional diagram, the genotypes tolerant to zinc deficiency with high yield in both optimal and zinc deficiency conditions were separated from each other. Also, the use of multivariate analyses was not only able to differentiate high-performance genotypes in both optimal and stress conditions, but also distinguished stable genotypes in stress conditions from unstable genotypes. So, Ma004, Ma027, Ma028, Ma038, Ma045, Ma083, Ma091, Ma105, Ma115 genotypes can be introduced as tolerant to zinc deficiency with stable performance for use in breeding programs.

Keywords

• Abiotic stress
• Hierarchical clustering
• Micronutrients
• Tropical cereal
• Yield

Main Subjects

• Breeding plants for stress conditions