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Vegetative Phase

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The growth period is subdivided into germination, early seedling growth and tillering. Germination and seedling development start when seed dormancy has been broken, the seed absorbs water and the temperature is between 10 and 40°C. Under anaerobic conditions, the coleoptile emerges first, the roots developing once the coleoptile has reached aerated regions of the environment. After the coleoptile emerges, it splits and the primary leaf develops.

Each rice stem is made up of a series of nodes and internodes, with nodes varying from 13 to 16. The internodes vary in length, depending on variety and environmental conditions, although internode length usually increases from the lower to the upper part of the stem. Each upper node bears a leaf and a bud, which can grow into a tiller.

Tillering

The tillering stage starts as soon as the seedling is self-supporting, generally when there are five leaves. This first tiller develops between the main stem and the second leaf. When the sixth leaf emerges, the second tiller develops, between the main stem and the third leaf. Tillers growing from the main stem are called primary tillers and may generate secondary tillers, which may in turn generate tertiary tillers.

Although the tillers remain attached to the plant, at later stages they are independent because they produce their own roots. Thus, the tillering stage is characterised by active tillering, a gradual increase in plant height and leaf emergence at regular intervals. Tillering generally finishes at panicle initiation.

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Varieties differ in their tillering ability, which is also affected by environmental factors such as spacing, light, nutrient supply and cultural practices. Indeed, some tillers are ineffective because they do not bear panicles, the number of tillers and the percentage of ineffective tillers depending on the variety and growing conditions. Although a high percentage of ineffective tillers may appear undesirable, a high tiller number per plant can provide crop tolerance and compensation for dead tillers caused by insects or diseases.