Evaluation of genetic diversity of maize lines (Zea mays L.) based on agro-morphological traits using factor analysis under zinc deficiency conditions

The first step in breeding programs is to use the genetic diversity among existing populations, cultivars and lines. Maize is used as a model plant to study the genetics of various traits. Compared to other crops, maize has a high demand for zinc (Zn) and is known as an indicator of zinc deficiency in the soil. In terms of climatic conditions, Iran is located in a arid and semi-arid region, and there is a lack of micronutrients specially Zn in this region. Lack of nutrients such as Zn is one of the important abiotic stresses that affects the growth and development of plants including maize. The objective of this study was to evaluate the genetic diversity of a number of corn lines under normal and zinc deficiency conditions.

To assess the genetic diversity of 95 maize lines using agro-morphological traits, an experiment was carried out in alpha lattice design in two replications under two normal (use of zinc sulfate fertilizer) and zinc deficiency (no use of zinc sulfate fertilizer) conditions in Zabol Agricultural Research Center during two years. The studied maize lines were obtained from Razi University of Kermanshah, Khorasan Razavi Agricultural and Natural Resources Research Center, and Seed and Plant Improvement Institute (SPII) in the form of research project No. 94/101/T.T. approved by Biotechnology Institute of Urmia University. Twenty-nine traits were measured and recorded. Combined analysis of variance of the studied traits under normal and zinc (Zn) deficiency conditions were performed using SAS ver. 9.4 software. Other statistical analyzes including descriptive statistics, Pearson correlation coefficient, forward stepwise regression and factor analysis method were done using R software by pastecs, corrplot, olsrr, and psych packages, respectively.

The results of this study revealed high phenotypic variation among the studied maize lines for all investigated traits under both normal and zinc (Zn) deficiency stress conditions. The results of analysis of variance confirmed the presence of high phenotypic diversity among maize lines. All traits were affected by environment, and a statistically significant difference was observed between two environments for the all measured traits in maize lines. Genotype × environment interaction was also significant for most of the studied traits. Descriptive statistics showed a considerable diversity among the lines, and the highest diversity in both normal and zinc deficiency conditions was observed for yield per unit area, economic yield, and number of grains per cob. In correlation analysis, weight of five cobs, number of grains per cob, and 100-grain weight showed a positive and significant correlation with economic yield in both normal and zinc deficiency conditions. Therefore, these three can be introduced as important traits in the initial selection of zinc deficiency tolerant lines. In factor analysis of morphological traits using the parallel analysis method, four hidden and independent factors were determined under both normal and zinc deficiency conditions, which explained 63% and 57% of the total variation of the lines, respectively. Based on the results of the factor analysis, the traits number of days to tasseling, number of days to pollen emergence, number of days to cob emergence, plant height, ear diameter and width, number of grains per cob, economic yield, yield per unit area, and harvest index with high degree of commonality under both normal and zinc deficiency conditions, can be suggested as key traits for the selection of zinc deficiency tolerant lines.

The results of this research showed that there is a high genetic diversity among the studied maize lines in terms of morphological traits under both normal and zinc deficiency stress conditions. It makes it possible to use these lines in breeding programs as a valuable genic source to improve the performance of lines and produce improved lines under normal and zinc deficiency conditions.