Assessment of Stress Indices in Elite Single-Cross Maize (Zea mays L.) Hybrids Under Low and Optimal Nitrogen Conditions using the iPASTIC Toolkit

Low soil nitrogen is a significant stress factor, often leading to reduced maize (Zea mays L.) grain yield. This study assessed the impact of low nitrogen on grain yield and agronomic traits of 10 single-cross extra-early provitamin A quality protein maize hybrids developed via Griffing's diallel method IV. A split-plot trial with four replications set up in a randomized complete block design was conducted under two nitrogen conditions (30 and 90 kg N ha⁻¹) as main plots, with the hybrids and a local check as sub-plots. Grain yield and related traits were measured under different nitrogen levels, and stress indices were calculated. Significant yield differences among hybrids were observed across nitrogen environments. Hybrids TZEEIORQ 63 × TZEEIORQ 53 and TZEEIORQ 63 × TZEEIORQ 52 performed best under both conditions, with TZEEIORQ 63 × TZEEIORQ 53 yielding 62.4% higher than the average of other hybrids and comparable to the local check. Stress indices, including mean productivity, geometric mean productivity, harmonic mean, stress tolerance index, and yield index, showed strong positive correlations with grain yield, effectively predicting low nitrogen tolerance. Multivariate biplot analysis linked TZEEIORQ 63 × TZEEIORQ 53 closely with these indices, while rank sum analysis consistently identified TZEEIORQ 53 × TZEEIORQ 52, TZEEIORQ 63 × TZEEIORQ 52, and TZEEIORQ 63 × TZEEIORQ 53 as tolerant to low nitrogen. Upon further testing, these hybrids may be suitable for cultivation in low soil nitrogen areas where farmers cannot afford optimal fertilizer application.