Effect of high density planting on grain yield and yield components of promising hybrids and parental lines of maize (Zea mays L.)

High plant density is considered as a stress that affects growth and developmental stages of crops throughout the life cycle. Results of previous studies have indicated that high yielding maize cultivars under high-density planting conditions are better adapted to most environmental stresses. Therefore, maize breeders use high plant density to identify cultivars tolerant to environmental stresses. The present study was conducted with the objective of evaluating 97 promising hybrids and parental lines of maize under high plant density planting conditions, facilitating the identification of cultivars tolerant to unfavorable environmental conditions.

This study consisted of four seperate experiments conducted on 21 early-maturity lines (first trial), 26 late-maturity lines (second trial), 24 early-maturity hybrids (third trial), and 26 late-maturity hybrids (fourth trial) of maize. The experiments were carried out in randomized complete block design with three replications at research field of Seed and Plant Improvement Institute, Karaj, Iran, in 2020 and 2021 growing seasons. The late- and early-maturity lines and hybrids were cultivated at plant densities of 140000 and 160000 plants.ha-1, respectively. Grain yield, number of grain rows ear-1, grain number row-1, 1000 grain weight, grain number plant-1 and test weight (hectoliter) were measured and recorded.

The results showed considerable variations in grain yield of maize hybrids and parental lines across different trials. In the first trial, line No. 12 with 8262 kg.ha-1 had the highest grain yield.  In the second trial, the highest grain yield (6025 kg.ha-1) obtained from line No. 12. In the third trial, hybrid No. 1 had the highest grain yield (9594 kg.ha-1), while in the fourth trial, hybrid No.10 with 8313 kg.ha-1 had the highest grain yield. Principal component analysis also indicated that the t suitable adapted genotypes for cultivation under high-density planting conditions included; early-maturity line KE781010/521, the late-maturity line K47/2-2-1-2-2-1-1-1, early-maturity hybrid K1263/17×MO17, and late-maturity hybrid K47/2-2-1-3-3-1-1-1×K166B.

Based on the results of all four experiments, which demonstrate significant and positive correlation between grain yield and grain number row-1, grain number plant-1, and ear number plant-1, it can be concluded that maize genotypes adapted to high plant density planting conditions produce more grains and ears in high plant density conditions are better adapted to environmental stresses.