The growth stages of wheat vary with specific time period that depend on physiological changes within the plant. It is very important to identify these growth stages.
Because these are related with different physiological and morphological changes in plant like tillering, booting, flowering, grain filling and ripening etc. Wheat have also three development stages Foundation, construction and production. The efficiency of field application inputs like irrigation, fertilizer, pesticide can enhance efficiently when they are applied at certain crop stage.
There are many staging systems to describe wheat development stages but Zadoks system is the most commonly accepted system. So, efficiently understanding of these growth stages are one of the basic keys for a successful research in wheat.
Wheat is the main staple food of the world. It has largest cultivated area over the world as compared to other crops. Wheat responds better if inputs applied on specific growth stage. There are three development stages (foundation, construction, production) of wheat. Foundation stage initiate from seed emergence to stem elongation, construction stage starts from first node detachable from flowering. It is very critical yield stage.
The production phase starts from flowering to ripening There are many scales to measure the growth stages of wheat like Feeks scale, Zadoks and Haun scales. The Feeks system mainly describe numerically stages like tillering and ripening but it gives not enough detail as compared to Zadoks system. Leaf production stage by length of each emerging leaf can be expressed by Huan system.
The Zadoks system is the popular system mainly it consists of two divisions, first division consists the principal growth stages of development from germination to ripening and the other is subdivision these stages. Being able to know sensitive growth stages of wheat for water and nutrition requirements, can apply on certain stage to get ultimately high yield.
The vegetative stage of wheat can be classified into three stages: tillering, jointing and booting stage. After the reproductive growth, wheat plant still starts its vegetative growth in plant height and accumulation of dry matter other than just grain because wheat has intermediate growth type.
The effect of temperature, water stress, disease, insects and weeds can be efficiently managed with a clear picture of relationship of plant responses with growth stages.
Wheat Growth Stages
a) Germination and Seedling
Germination is the first stage, during this stage proper temperature, seed depth and moisture contents are important to germinate the seed. It occurs from the dry seed to coleoptile emergence. Almost 4-5 days are required to produce one leaf Wheat seed can germinate easily from 12 °C to 25 °C temperature.
If there is optimum condition, seed can germinate within seven days. Germination mainly depended on depth of seed and energy that is stored in endosperm of the seed. The energy that required to seedling is mainly depended on energy and nutrients that are stored in seed.
Germination started when grain absorb water called imbibition by breaking its dormancy. Seminal roots are developed and coleoptile pressing the growing point to soil surface.
The seedling stage formed when first leaf appeared and completed when first tiller emerged. At this stage 3 leaves and six seminal roots support plant.
Usually tillering started when crop have almost 3-4 leaves. These are the lateral shots rises from the base of the stem. Each tiller has the ability to produce a spike for yield contribution that’s why tillering stage is important for yield. The numbers of tillers vary among verities.
After the formation of all tillers stem elongation stage formed. Major yield loss can occur if crop is infested by weeds during this stage because weeds compete for light, canopy development and nutrients with wheat plant.
At this stage application of nitrogen is important for development and size of leaf and enhancing the tillers numbers of plant and Manganese helps in the photosynthetic proteins and enzymes structure.
The formation of crown system followed after tillers appearance and emergence of second crown root system. This system helped the plant to absorb nutrients and water requirement during the growing stages.
c) Stem Elongation or Jointing Stage
During stem elongation Nitrogen, phosphate, potassium, Sulphur, manganese and zinc play a positive contribution in yield like phosphate provide the energy for growth and development, potassium help in plant water regulation and manganese for structure role of photosynthetic enzymes and proteins .
After jointing stage starts, internode area elongated, stem becoming long that will carry the head of plant. Formation of node o plant can be checked without dissecting the stem by pressing the stem base with fingers. After the formation of flag leaf stem elongation stage comes to end.
d) Booting Stage
The developing head within the sheath of the flag leaf becomes visibly enlarged during the booting stage. The booting stage ends when the first awns emerge from the flag leaf sheath and the head starts to force the sheath open.
e) Heading & Flowering
Heading stage started when the head is completely emerged from the stem. After this, Flowering or anthesis stage formed when pollens are released by anthers for pollination. Pollination is commonly fast, the duration of pollination in a single head is around 4-5 days.
Wheat crop is self-pollinated crop and grains per spike are calculated by the numbers of the flowers those are pollinated Physiologically it is the most sensitive stage and can impacted by temperature variations.
Variations in temperature and water stress in this stage can reduce overall yield by reducing numbers of grains. The heading stage initiates from the appearance of the tip of the head from the sheath of flag leaf to fully emerged head but still flowering not started. The occurrence of fertilization and pollination completed in this stage.
f) Dough Stage
Dough stage started after the flowering completion and this is the initial kernel formation step. Dough stage consists milk, soft dough and hard dough. During dough stage mostly grain dry weight protein and starch contents accumulated. Hard dough stage expressed the maximum dry weight with around 30% moisture contents.
Dough stage is also called physiological maturity. Nitrogen impacts on formation of green leaf, protein and size of grain and phosphate for remobilization of dry matter for yield enhancing and boron play a vital role in viability of pollen. Initially grain development starts during dough stage.
The size of grain become increase during dough stage and grain formation become completed. The movements of food from stems, leaves and spike to the kernel completed after hard dough stage, at this stage kernel contains almost 30% of the water.
During this period plant turns into yellow straw color and the seed become hard and the moisture level of seed at that time around 13 to 14 %.
Critical Growth Stages
Efficient cultivation of a crop depended upon management on its critical sensitive growth stages. So, we can get maximum yield by understanding behavior of a crop. The sensitivity of wheat crops against different stresses varies with verities like some verities have more resistance against salinity and water stress as compared to other verities.
The scientists have produced combination of verities by crossing that have a wide range of adaptations in different environments. So, to understand the responses of crop on growth stages can help to modify crop management for better yield.
Wheat Grain yield = (number of heads) x (grains per head) x (grain weight)
The numbers of spikes depended on number of seedling and tillers that are produced. Tillering formation is suitable under moist, warm weather and soil fertility and level of nitrogen fertility.
Tillering production must be balanced for a better yield. The formation of tillers and its development depend on environmental characteristics. Stem elongation and booting stage is critical stage for drought and heat stress and by effecting it increase mortality rate of tillers.
For example, almost 250,000 number of tillers dead in winter per day per acre due to drought and heat stress in 1988 at Saskatoon. After the severe stress condition of environment only the main stem remained. If crop phase environmental stress during the flag leaf appearance can affect spikelets.
The main aspect of yield losses starts when there will loss of tillers at the start of stem elongation. Drought stress on all stages cause grain yield loss. During stem elongation stress has more sensitivity as compared to other stages. Salinity effect on booting stage is more sensitive for yield and growth of wheat.
The understanding of different growth stages is very important for cultural practices and experimental work because every growth stage required different inputs like irrigation, nutrients and environment conditions for proper growth.
Crop nutrients absorbing ratio is also vary with growth stages. So, it is necessary to apply inputs according to the requirement of crop on different stages. We can increase inputs application efficiency by applying on certain stage and can study the effects of different stress on stages of crop.
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5. Bauer, A., D. Smika, and A. Black. 1983. Correlation of five wheat growth stage scales used in the Great Plains. USDA-ARS, Peoria, Ill.
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Muhammad Roman, Abdul Rehman, Muhammad Ali, Sarwan Khan , Yousaf Yahya Ali Sewar
School of Soil and Water Conservation, Beijing Forestry University, China.