GROWTH PHASES AND STAGES OF RICE PLANT
The life cycle of rice plant may be divided into the following three phases:
1. Vegetative phase : From germination to panicle initiation.
2. Reproductive phase : From panicle initiation of flowering.
3. Ripening phase : From flowering to maturity.
These phases may be subsequently divided into different growth stages.
Vegetative phase :
This phase begins with the seed germination, which is signified by the emergence of radicle or coleoptile in the germinating embryo. During the vegetative phase, the plant undergoes the following stages:
I. Seedling stage : This stage follows seed germination and the seedling develops germinal and lateral roots. Seedling stage is generally considered from germination until the plants develop the fifth leaf. During this stage, the seedling absorbs food from the endosperm.
II. Transplanting stage : Only the transplanted rice plants undergo this stage. It covers the period from uprooting of the seedling to full recovery. Direct seeded rice plants do not undergo through this stage.
III. Tillering stage : This stage starts with the appearance of the first tiller from the auxiliary bud in one of the lower most modes. The number of tillers increases, at a point more rapidly (active tillering stage), until the maximum tiller number (maximum tillering stage) is reached. Then some tillers die, the number of tillers declines and levels off. The plant stops tillering after the tertiary tillers have been produced.
Reproductive phase :
During the reproductive phase, the plant undergoes the following stages :
I. Panicle initiation stage : The reproductive phase begins before reaching the stage of producing maximum number of tillers, at about the time of the highest tillering activity or thereafter. This phase is marked by the initiation of the panicle primordial of microscopic dimension on the growing shoot.
II. Booting and internode elongation stage : As the young panicle develops, It becomes visible to the naked eye in a few days. This marks the beginning of the booting stage.
The time of occurrence of internode elongation stage differs among varieties. With late maturing varieties, the accelerated elongation of the upper internodes may begin considerably earlier than the reproductive phase. With early maturing varieties, elongation may begin after panicle initiation.
III. Heading stage : This stage is marked by the emergence of panicle tip out of the flag leaf sheath. Emergence continues until 90% of the panicles are out of the sheaths.
IV. Flowering stage : Flowering or blooming or antheis begins with the protrusion of the first dehiscing anthers in the terminal spikelets on the panicle branches. Flowering continues successively until all spikelets in the panicle bloom. Pollination and fertilization then follow.
RIPENING PHASE :
The rice grain develop after pollination and fertilization. Grain development is a continuous process and the grain undergoes distinct changes before it fully matures.
I. Milk stage : The contents of the caryopsis are first watery but later turn milky in consistency.
II. Dough stage : The milky caryopsis turns into soft dough and subsequently into hard dough.
III. Maturity stage : The individual grain is mature when the caryopsis fully developed in size and is hard, clear and free from greenish tint. This stage is completed when more than 90% of the grains are fully ripened.