Wheat, a cereal grain cultivated globally, serves as a fundamental food source. It progresses through distinct developmental phases, each marked by specific changes in its structure and function. Understanding these sequential growth stages provides insight into the plant’s life cycle, from seed to mature grain.
Standard Systems for Tracking Growth
To precisely identify and communicate about wheat development, standardized classification systems are employed. The Feekes scale, developed in the Netherlands, focuses on the plant’s external morphological development. This scale uses whole numbers (1-11) to denote major growth milestones, such as tillering or heading, offering a straightforward way to categorize visual progress.
The Zadoks scale, a more comprehensive system, uses a two-digit decimal code to describe both the main stem and tillers, providing greater detail for specific substages. The first digit indicates the principal growth stage (e.g., seedling development or stem elongation), while the second refines the progression within that stage. For instance, Feekes 6 corresponds to the first node detectable, while Zadoks 30 indicates the beginning of stem elongation. These systems facilitate consistent communication among researchers and farmers, helping to time various agricultural practices.
Early Stages: From Seed to Tillers
Wheat germination begins when the seed absorbs sufficient water. The radicle, or embryonic root, is usually the first part to emerge, anchoring the nascent plant and absorbing nutrients. Shortly after, the coleoptile, a protective sheath, pushes through the soil, encasing the first true leaves. This marks the seedling establishment phase, where true leaves unfold and begin photosynthesis.
As the plant establishes, it enters the tillering stage, important for yield potential. Tillers are side shoots developing from buds at the base of the main stem, each capable of producing its own head of grain. This branching increases the number of grain-bearing stems per plant, directly influencing the final yield. Root development also continues, forming a strong foundation for nutrient and water uptake.
Mid-Season Stages: Stem Elongation to Flowering
Following tillering, the plant transitions into the jointing or stem elongation phase, characterized by rapid vertical growth. The first detectable node, or “joint,” appears above the soil line, signifying the beginning of stem internode elongation. This upward growth positions developing reproductive structures for light capture and grain fill.
The plant then enters the boot stage, where the flag leaf, the uppermost leaf, fully emerges. During this time, the immature wheat head, or spike, swells within the flag leaf’s sheath, preparing for emergence. This stage is visually distinct due to the noticeable bulge at the top of the stem. Soon after, the heading stage commences as the wheat head fully emerges from the flag leaf sheath.
The final stage in this mid-season period is flowering, also known as anthesis. Pollen is shed from the anthers within the wheat head’s florets. Fertilization occurs as pollen lands on the stigma, leading to individual kernel development. This reproductive event determines the number of grains that will develop on each head.
Late Stages: Grain Formation and Ripening
Once fertilization is complete, the wheat plant enters the grain formation and ripening stages, focusing on developing kernels within the head. The first observable phase is the milk stage, where developing kernels are soft and contain a milky white fluid when squeezed. At this point, the grain rapidly accumulates water and early carbohydrates.
As kernels mature, they transition through the soft dough and hard dough stages. In the soft dough stage, the milky fluid thickens to a soft, dough-like consistency, indicating further starch accumulation. The hard dough stage follows, where kernels become firm and more difficult to dent, signaling continued drying and hardening of the grain.
The plant reaches physiological maturity when the grain achieves its maximum dry weight, meaning no more nutrients or dry matter are transferred from the plant to the kernel. This point is visually indicated by the loss of all green color from the plant, particularly the head and flag leaf. Following physiological maturity, the grain continues to dry down in the field until it reaches an optimal moisture content for harvest, known as harvest maturity.