Morphological features and Developmental stages

Zea mays (maize) is a monocot from the Poaceae family, essential worldwide for food, feed, and biofuel. Its morphology, from seed to mature plant, plays a key role in its development and adaptation. Maize seeds, or kernels, consist of the pericarp (protective outer layer), endosperm (nutritive starch tissue), and embryo (future plant). Kernels vary in color, typically yellow, but can be red, blue, or multicolored depending on genetics.

The root system is fibrous, with adventitious roots replacing the primary root. These roots enhance nutrient and water absorption, aided by mycorrhizal fungi. The stem is cylindrical, solid, and hollow at the internodes, allowing flexibility. Internodes elongate rapidly, contributing to plant height.

Maize leaves are long, narrow, and lanceolate, arranged alternately along the stem. The leaf blade is responsible for photosynthesis, while the sheath surrounds the stem. This arrangement maximizes light capture and minimizes shading.

Maize has dioecious inflorescences: the tassel (male) produces pollen, while the ear (female) forms in the leaf axils. Wind pollinates the plant, with each silk on the ear corresponding to a kernel. Fertilized ovules develop into kernels, protected by husks. The maize fruit is a caryopsis, a single-seeded dry fruit with starchy endosperm. The kernels mature and dry, completing the reproductive cycle.

Maize’s morphological traits, including its fibrous root system, tall stem, and wind-pollinated flowers, enable it to thrive in diverse environments, ensuring its global agricultural significance. Understanding these features is vital for improving crop yields and resilience.

The morphological development of Zea mays L. follows distinct phases characterized by specific structural and functional changes. During seedling growth, the kernel's tripartite structure (pericarp, endosperm, and embryo) facilitates hypogeal germination, where the radicle emerges first, followed by the coleoptile-protected plumule. The mesocotyl elevates the coleoptile while seminal roots provide initial anchorage and nutrient uptake.

Standardization of Maize Growth Stages

To facilitate uniformity in maize research, growth stages are standardized, allowing for consistent comparisons across environments and treatments. Growth stages are categorized into two phases: vegetative (V) and reproductive (R). A crop reaches a stage when at least 50% of plants exhibit corresponding traits.

Vegetative growth is marked by the development of a modular stem architecture comprising nodes and internodes, with the growing point remaining subterranean for 3-4 weeks post-planting. Leaf initiation occurs within 4-5 weeks, producing 16-23 leaves in an alternating phyllotactic pattern. Each leaf consists of a blade, sheath, and collar, with leaf emergence occurring approximately every three days under optimal conditions. The root system transitions from seminal to adventitious, with crown roots developing post-emergence and eventually reaching depths of 2.5 meters.

The reproductive phase begins with tassel initiation approximately 30 days after sowing. The monoecious nature of maize is evidenced by spatially separated male and female inflorescences. The terminal tassel produces up to 25 million pollen grains over 5-8 days, while lateral branches develop into ear shoots. Female inflorescence development is characterized by paired spikelets containing single fertile ovules, potentially producing 500-750 ovules per ear. The anthesis-silking interval serves as a key indicator of reproductive synchrony and stress tolerance.

Grain filling proceeds through distinct stages: blister (R2), milk (R3), and dough (R4), characterized by progressive accumulation of carbohydrates and decreasing moisture content. Maturity encompasses the dent stage (R5) and physiological maturity (R6), marked by black layer formation at approximately 35% kernel moisture content. Grain development follows a sigmoidal pattern with lag, linear, and final phases, culminating in maximum dry matter accumulation.

This developmental sequence demonstrates the complex coordination of vegetative and reproductive growth processes that contribute to maize's remarkable productive potential, with a single seed capable of producing 400-700 kernels within approximately 115 days under optimal conditions.

References

1. Kling, J. & Edmeades, G. (1997). Morphology and growth of maize: IITA research guide, No. 9. Ibadan, Nigeria: IITA, (p. 36).