Heat Stress Levels in Maize and its effect

Theheat stress indicators for maize are defined based on moderate heat damage,with critical temperatures set at 36°Cduring the seedling stage, 32°C during the reproductive stage, and 28°C duringthe maturity stage. Temperatures exceeding 32°C during flowering hinder pollination. Based on the mean temperature across the entire growthperiod, heat stress is classified as follows:

ü   Mild heatstress (29°C): Results inan 11.9% yield reduction.

ü   Moderateheat stress (33°C):Leads to a 52.9% yield reduction.

ü   Severeheat stress (36°C):Causes complete crop failure.

Prolongedexposure to high temperatures (38°C– 39°C) exacerbates heat damage, with longer durations increasing severity and hindering recovery. the primary effects of high temprature on maize growth include:

1. Impact onPhotosynthesis

Underheat stress, the activity ofphotosynthetic enzymes declines, and chloroplast structures are damaged, leading to stomatal closure and reducedphotosynthetic efficiency. Concurrently, respiration rates increase, elevating energy consumption andreducing dry matter accumulation. Prolonged exposure to 38–39°C intensifies plant damage,prolonging recovery time.

2. ShortenedGrowth Cycle

High temperatures acceleratephysiological and biochemical processes, shortening each growth stage. Keyimpacts include:

ü   Reducedduration of ear differentiation,leading to fewer florets and smaller ears.

ü   Prematuresenescence inlater growth stages, forcing early maturation.

ü   Shortened grain-filling period, reducing dry matter accumulation, kernel weight, test weight, and overall yield and quality.