zea mays

07.05.2025 | 13:34 (UTC -3)

The corn (zea mays), one of the most important agricultural crops globally, belongs to the Poaceae family and stands out for its versatility, nutritional value and industrial applications.

With a global production of around 1,2 billion tonnes in 2024 (FAO), corn is essential for food security, serving as human food, animal feed and raw material for industries such as ethanol and oil.

Adaptable to tropical and temperate climates, at altitudes from 0 to 3.800 meters, it is a strategic crop for developing countries.

Taxonomy and morphology

zea mays It is an annual herbaceous plant with an erect stem (1,5–3 m), alternate lanceolate leaves and a root system composed of primary and adventitious roots. The male inflorescence (tassel), located at the apex, produces anemophilous pollen, while the female inflorescence (mazorca) is formed in the leaf axils, with filiform stigmas capturing the pollen.

The grains vary in composition and color, influencing their uses:

Harinous corn (Zea mays amylaceus): floury endosperm, ideal for flours.

Hard corn (Zea mays indurata): vitreous endosperm, used in feed and ethanol.

Sweet corn (Zea mays saccharata): high sugar content, for fresh consumption.

Purple grains have anthocyanins with an antioxidant capacity of 300–500 µmol Trolox/g (Silva et al., 2023).

Biology

zea mays It is a tall annual grass with a single, solid stem that can reach up to 3 meters in height. Its leaves are linear and arranged alternately, and its root system, which is predominantly shallow, is composed of primary, seminal and adventitious roots, which ensure the absorption of nutrients and water. As a C4 plant, it uses the Hatch-Slack pathway for carbon fixation, providing high photosynthetic efficiency in hot, dry climates.

Corn is monoecious, with male flowers (tassel) at the apex of the stem and female flowers (mazorca) in the leaf axils. The tassel produces up to 10 million pollen grains per plant, released continuously for about a week, with a diameter of 94–103 µm and viability of up to 2 hours, which can be extended in high humidity (Canadian Food Inspection Agency).

Pollination is predominantly anemophilous, with a self-pollination rate of approximately 5%, influenced by the size of the tassel and environmental conditions. Pollen dispersion occurs up to 30 meters, but can reach hundreds of meters with horizontal winds.

The mazorcas, protected by bracts (straws), contain 4–30 rows of ovules, each with the potential to develop 300–1.000 grains, depending on the cultivar and environmental conditions. The stigmas (silks) grow up to 30,5 cm, emerging from the base to the apex in 3–5 days, with trichomes that aid in pollen capture. The synchrony between pollen release and silk emergence is crucial for high grain set, but stresses such as drought can increase the anthesis-silking interval, reducing productivity.

Embryogenesis occurs in three phases:

Proembryo: 12–24 cells formed within 100 hours postfertilization, with basal cell forming the suspensor and apical cell generating 9–18 dense cells.

Formation of embryonic axis: meristems and embryonic axis develop until ~13 days, with coleoptilar embryo at 14–15 days.

Maturation: accumulation of reserve products, with embryo reaching ~50 mg fresh weight in 30–40 days.

The fruit is a caryopsis, composed of embryo, endosperm (80%) and fruit wall. Grain filling lasts ~8 weeks, passing through stages such as blister (10–14 days post-fertilization), milk, dough and physiological maturity (55–65 days post-seed emergence), marked by the formation of the black layer.

Corn can hybridize with teosintes (zea mays ssp. mexicana and parviglumis), forming fertile hybrids, but this is irrelevant in regions without teosintes, such as Brazil. Experimental crosses with Tripsacum ou Coix lachryma-jobi are possible under controlled conditions, but result in sterile hybrids or require embryo rescue.

Corn growth is divided into vegetative and reproductive stages, described by the BBCH scale:

Germination (BBCH 00–09): begins with water absorption (~30% of seed weight), with radicle and coleoptile emerging. Requires soil temperatures ≥15°C; below 10°C, growth is inhibited.

Leaf development (BBCH 10–19): Leaves emerge sequentially, with 18–22 leaves total. The growing point remains underground until the 5th leaf stage, tolerating frosts down to -3°C.

Stem elongation (BBCH 30–39): rapid stem growth and formation of nodal roots. High demand for nitrogen and water; water stress for ≥4 days reduces productivity.

Inflorescence emergence (BBCH 50–59): tassel emerges, and mazorca shoots develop. Roots reach ~1,8 m deep.

Flowering (BBCH 60–69): pollen release and silk emergence. Water stress can reduce yields by up to 50%; temperatures >32°C inhibit pollen.

Fruit development (BBCH 70–79): grains pass through blister, milk and dough stages, requiring 70–80% soil moisture. Optimal temperatures of 20–22°C.

Maturation (BBCH 80–89): grains reach physiological maturity (50–55 days for early hybrids), with moisture content of 30–38% and formation of the black layer.

Senescence (BBCH 90–99): plant dries out, producing ~1,5 t of straw per ton of grain.

Corn physiology

Photosynthesis: As a C4 plant, corn utilizes the Hatch-Slack pathway, fixing CO2 into oxaloacetate in the mesophyll cells before transferring it to the bundle sheath cells for the Calvin cycle. This confers high water efficiency and tolerance to high temperatures.

Water relations: high water demand, especially in the vegetative and flowering stages. The shallow root system makes corn sensitive to drought, particularly during seed emergence, which can compromise grain formation.

Nutrient absorption: requires high levels of nitrogen (N), phosphorus (P) and potassium (K). NO is essential for leaf development and photosynthesis, while P supports root growth. Micronutrients such as zinc and iron are crucial for enzyme functions.

Temperature response: optimum growth between 18–32°C. Temperatures >35°C cause heat stress, reducing pollen viability and grain filling. Frost damages seedlings, requiring replanting if the growing point is affected.

Light requirements: full sun plant, requiring 6–8 hours of direct sunlight daily. Limited shade tolerance, with reduced productivity in low light conditions.

Response to environmental stresses

Dry: reduces growth, delays development and decreases yields, especially during flowering and grain filling.

Heat stress: temperatures >35°C inhibit pollen production and reduce grain formation, shortening the filling period.

Nitrogen deficiency: causes chlorosis, stunted growth and lower productivity, affecting photosynthetic efficiency.

Pests and diseases: susceptible to insects and pathogens, which impact physiological processes and yield.

Plant health

Corn faces diseases such as:

Tropical rust (Puccinia polysora): yellowish leaf lesions.

White spot (Pantoea ananatis): white spots on the leaves.

Stem rot (Fusarium spp.): stem rot.

Stripe virus: chlorosis and necrosis.

In terms of pests, the following can be mentioned:

Sugarcane borer (Diatraea saccharalis): damages stalk, reduces yield components, can cause plant death. Management: Bt corn, seed treatment, control of eggs and small larvae with insecticides.

Neck borer (Elasmopalpus lignosellus): reduces productivity by up to 70%, causes "dead heart". Management: seed treatment with systemic insecticides, increase irrigation to reduce population.

Corn leafhopper (Dalbulus maidis): transmits stunting, reduces nutrient absorption. Management: crop rotation, eliminate volunteer corn, treated seeds, avoid late sowing

Corn earworm (Helicoverpa zea): feeds on grains, reduces productivity, predisposing to pathogens. Management: Bt corn, toxic baits, release of Trichogramma spp.

Fall armyworm (Spodoptera frugiperda): reduces productivity by >50%, attacks leaves, cartridge, can section plants. Management: Bt corn, seed treatment with systemic insecticides, selective post-emergence application

Wheatworm (Pseudaletia sequax): consumes leaves, affects photosynthesis, tolerant to Bt >0,8 cm. Management: desiccation of cover 3 weeks before, pre-sowing insecticides, pyrethroids.

Old World caterpillar (Helicoverpa armigera): attacks leaves, stigmas and grains, similar to H. zea. Management: Bt corn, seed treatment, release of Trichogramma spp.

Threadworm (Agrotis ipsilon): cuts seedlings at the base, reduces plant population, causes "dead heart". Management: seed treatment, application of granular insecticides at sowing, toxic baits.

Pinworm (Diabrotica speciosa): reduces root system, causes "gooseneck", affects yield. Management: application of granular insecticides at sowing, soil spraying, insufficient biological control.

Brown stink bug (euchistus heros): causes deformed leaves, reduces productivity, affects growth. Management: control in soybeans, seed treatment, pre- and post-emergence insecticides.

Bedbugs (Dichelops furcatus, Dichelops melacanthus): damage meristem, cause deformed leaves, reduce productivity. Management: control in soybeans to prevent migration, seed treatment, pre- and post-emergence insecticides.

Corn aphid (Rhopalosiphum maidis): causes sooty mold, reduces photosynthesis, transmits mosaic virus. Management: seed treatment with systemic insecticides, control if >50% plants have >100 aphids.

Some of the weeds that cause problems for crops: