How does early defoliation influence the morphophysiology and biochemical characteristics of maize?

Defoliation is a type of mechanical stress, and few studies have investigated this process in the early stages of maize development. Pest attacks, hail and machinery traffic have increased in recent decades, thus increasing this stress and potentially leading to losses. Furthermore, there are corn production systems in Brazil where early defoliation naturally occurs. Thus, the objective of this study was to determine the morphophysiological and biochemical changes in maize subjected to early defoliation and their effects on recovery from this stress. The experiment was performed in pots, and the plants were subjected to two treatments at the four fully expanded leaf stage: without defoliation (control) and with defoliation. Morphometric parameters, such as gas exchange, leaf pigment and biomolecule content, phytohormone content, root morphology and leaf anatomy, were evaluated at seven and fourteen days after defoliation. Compared with the control plants, the defoliated corn plants were shorter in height, stem diameter, length, surface area, root diameter and volume, dry biomass and leaf anatomy. However, photosynthesis, chlorophyll content and nutrient content were similar in both treatments. After seven days of treatment, the amino acid content increased in the defoliated plants, and after fourteen days, the reducing sugars, amino acids and proteins decreased in these plants. The levels of gibberellins and salicylic acid were greater in plants subjected to defoliation. The reestablishment of corn plants after defoliation occurred through the action of gibberellins and salicylic acid, which promoted the growth of aboveground biomass, maintenance of chlorophylls and gas exchange. The reallocation of amino acids and reducing sugars also contributes to the formation of new leaf primordia in defoliated plants.