EVOLUTION OF CROPS:

RICE
What is
Rice?
Rice is one of the oldest cultivated crop. It
is a seed of a semi-aquatic grass (Oryza sativa) that
is cultivated extensively in warm climates in many
countries, including the United States, for its edible
grain. It is a staple food throughout the world.
 1. Flag leaf: The flag leaf is the uppermost leaf of the rice
Parts Of Rice plant. It is called the flag leaf because it is usually the first
leaf to emerge and it "flags" or droops over the rest of the
plant.
2. Branch: A branch in a rice plant refers to a smaller stem
that grows out from the main stem. It can bear leaves,
flowers, or grains. Branches help in distributing nutrients
and water throughout the plant.
3. Secondary branch: A secondary branch is a smaller
branch that grows out from a primary branch. It further
enhances the distribution of nutrients and water within the
rice plant.
4. Main panicle axis: The main panicle axis is the central
stalk or stem of the rice plant's panicle. The panicle is the
flowering structure of the rice plant that contains multiple
spikelets. The main panicle axis provides support to the
spikelets and helps in their development.
5. Panicle base: The panicle base is the lower part of the
main panicle axis where the panicle attaches to the stem of
the rice plant. It serves as the point of connection between
the panicle and the rest of the plant.
6. Pedicel: A pedicel is a small stalk that attaches the
spikelet to the main panicle axis. It supports the spikelet
and allows for its movement and development.
7. Spikelet: A spikelet is the basic unit of the rice
inflorescence or panicle. It consists of one or more florets
enclosed by glumes (leaf-like structures). Each floret can
potentially develop into a rice grain.
1. Awn: refers to the long bristle-like structure that
extends from the hull or lemma of the rice plant.
2. Anther - is the male reproductive part of the rice
flower.
3. Filament- is the slender stalk that supports the anther.
4. Apiculi- are small projections or tips found on the rice
leaf blades.
5. Stigma- is the female reproductive part of the rice
flower.
6. Lemma- is the outermost bract or husk that covers the
rice grain.
7. Palea- is the inner bract or husk that covers the rice
grain, situated between the lemma and the grain.
8. Ovary- is the part of the rice flower that contains the
ovules. After fertilization, the ovary develops into the rice
grain.
9. Sterile Lemmas- are modified bracts that do not
produce flowers or seeds. They are usually present
above the fertile florets.
10. Rudimentary Glumes- are small, undeveloped
bracts that protect the developing florets. They are
located at the base of the spikelet.
11. Pedicel- refers to the stalk or stem that connects the
spikelet (cluster of flowers) to the main stem of the rice
plant.
Mode Of Pollination Benefits Of Rice
The mode of pollination in rice is primarily self-pollination. The rice has numerous benefits. Here are a few:
Rice plants have both male and female reproductive organs, 1. Staple Food: Rice is a staple food for more than half of
which are located in the same flower. The male reproductive the world's population. It provides a significant portion of
organ, called the stamen, consists of anthers and filaments the daily calorie intake for many people, especially in
that produce and release pollen. The female reproductive Asia.
organ, called the pistil, consists of a stigma, style, and 2. Nutritional Value: Rice is a good source of
ovary. During self-pollination, the rice plant's pollen is carbohydrates, providing energy for the body. It also
transferred from the anther to the stigma within the same contains essential vitamins and minerals such as vitamin
flower. This can occur through natural means, such as wind B, iron, and magnesium.
or gravity, or with the help of pollinators like insects. The 3. Versatility: Rice can be prepared and consumed in
pollen then travels down the style and fertilizes the ovary, various ways, making it a versatile ingredient in many
leading to the development of seeds. Self-pollination is cuisines. It can be steamed, boiled, fried, or ground into
advantageous for rice plants because it ensures a higher flour for different types of dishes.
rate of successful pollination and seed production. It 4. Economic Importance: Rice cultivation is a significant
reduces the dependence on external factors, such as economic activity in many countries. It supports
pollinators, and enhances reproductive efficiency. livelihoods for millions of farmers and contributes to local
and national economies.

These are just a few of the benefits of the rice plant.

■ Oryza sativa rice was first domesticated in the Yangtze River basin in China Most of the world’s rice is grown in tropics which
13,500 to 8,200 years ago. Cultivation, migration and trade spread rice around include countries of South and South East Asia, West Africa,
the world—first to much of east Asia, and then further abroad, and eventually to Central and South America. About 90% of the world crop lands
the Americas as part of the Columbian exchange. The now less common and production of this crop is concentrated in Asia, about 3% of
Oryza glaberrima rice was independently domesticated in Africa around 3,000 the areas under rice are in Africa (2.2% of world rice grain
years ago. Other wild rice species have also been cultivated in different production), 6% in America (6% of world production). Only 1% of
geographies, such as in the Americas. world rice crop land is found in Europe. The average productivity
of rice is the highest in Egypt i.e., 9.84 t/ha as against world’s
average of 4.05 t/ha.
Center Of Diversity Among the various rice growing countries of the world, India has
the largest area under rice and in case of production it stands
■ The center of diversity of the rice plant Oryza sativa is located in the Asia- next to China. In India, rice is the most important and extensively
Pacific region, specifically in the countries of China, India, Indonesia, grown food crop, occupying about 43 million ha of land.
Bangladesh, and Myanmar. These regions have a rich history of rice cultivation
and are home to numerous traditional rice varieties. In China, the Yangtze River
valley is considered one of the centers of diversity for Oryza sativa. India, being
one of the largest rice-producing countries, also has a significant contribution to
the genetic diversity of rice. Indonesia, with its diverse agroclimatic conditions,
has a wide range of rice varieties. Bangladesh and Myanmar also have a
diverse collection of traditional rice landraces.
Ancestors Of The Crop: Rice
Morphological Changes Of rice from before to now
The rice plant, scientifically known as Oryza sativa, has a rich history with
a long line of ancestors. The wild ancestor of cultivated rice is believed to The rice plant, Oryza sativa, has undergone several morphological
be either Oryza rufipogon or Oryza nivara, both of which are wild grass changes from its early domestication to modern cultivated varieties. Here
species native to Asia. These wild species are still found today in various are some of the key changes:
regions, particularly in Southeast Asia. Over time, humans selectively bred
and cultivated rice plants with desirable traits, leading to the development 1. Plant Height: Traditional rice varieties were generally tall, with long
of different rice varieties and subspecies. It's fascinating to explore the stalks that were prone to lodging (falling over) under the weight of the
evolutionary journey of the rice plant and the impact it has had on human grains.
civilization. 2. Tillering Capacity: Tillers are the side shoots that emerge from the
main stem of the rice plant. Traditional varieties typically had fewer
tillers.
3. Grain Quality: Over time, breeders have focused on improving grain
Chromosome Number: quality traits. As a result, modern rice varieties exhibit enhanced
nutritional value, better taste, and improved resistance to biotic and
abiotic stresses.
The rice genome (Oryza sativa; AA genome) is composed of
4. Root System: The root system of rice plants has also undergone
12 chromosomes (2n = 24) and has a total length of 430 Mb
changes. This allows the plants to access water and nutrients more
(megabase, a nucleotide length of 1000 000 base pairs)
efficiently, leading to improved growth and yield potential.
corresponding to about 1500 cM (centiMorgan, a genetic
unit of length measured by the crossing ‐over frequency in
genetic recombinations at meiosis). Rice has a relatively
small genome (430 Mb) compared with that of other
common cereals.
 Factors that contributed to the evolution
Comparison Of The Ancestor
The evolution of the rice plant, Oryza sativa, has been influenced
When comparing the ancestors of the rice plant, Oryza sativa, to the modern by several factors. Some of the key factors include:
cultivated varieties, there are several notable differences.
1. Genetic Diversity: The ancestors of Oryza sativa exhibited a higher level of 1. Natural selection: Over time, the rice plant has undergone
genetic diversity compared to modern cultivated varieties. Wild natural selection, where certain traits that were advantageous
2. Grain Size and Shape: The wild ancestors of rice had smaller and more for survival and reproduction were favored. This includes traits
varied grain sizes and shapes. such as disease resistance, drought tolerance, and seed
3. Yield Potential: Modern cultivated rice varieties have been bred to have a production.
higher yield potential compared to their wild ancestors. 2. Human cultivation: Rice has been cultivated by humans for
4. Disease and Pest Resistance: Wild rice species possess natural thousands of years, and this has played a significant role in its
resistance to a range of diseases and pests. Through breeding programs, evolution. Through selective breeding, humans have favored
modern cultivated rice varieties have been developed with enhanced traits such as high yield, desirable grain quality, and early
resistance to specific diseases and pests that are prevalent in different maturity. This
regions. 3. Genetic diversity: Rice has a high level of genetic diversity,
5. Adaptation to Cultivation Practices: Wild rice species are adapted to which has allowed for adaptation to different environmental
grow in diverse natural habitats, such as marshes, swamps, and riverbanks. conditions.
Modern cultivated rice varieties have been bred to adapt to specific 4. Environmental factors: Environmental factors, such as
cultivation practices, including flooded paddy fields and upland conditions. climate, soil conditions, and pest pressure, have also
influenced the evolution of rice.
These are some of the key comparisons between the ancestors of Oryza sativa
and the modern cultivated varieties. The These factors have collectively contributed to the evolution of
Oryza sativa, resulting in the diverse range of rice varieties that
exist today.
 Characteristics of current varieties
of the crop
Wild Relatives: The characteristics of the current varieties of the rice plant
Oryza sativa can vary based on the subspecies. Here are
The wild relatives of the cultivated rice plant, Oryza some general characteristics:
sativa, play a crucial role in the genetic diversity and 1. Japonica or Sinica Variety:
evolution of this important crop. - Sticky texture: The grains of Japonica rice are
1. Oryza rufipogon: Also known as the Asian wild known for their stickiness when cooked, making them
rice, Oryza rufipogon is considered the primary suitable for dishes like sushi.
wild ancestor of Oryza sativa. It is native to - Short grains: Japonica rice has shorter grains
Southeast Asia and possesses a wide range of compared to other varieties.
genetic diversity. - Mild flavor: It has a mild and slightly sweet flavor.
. - High moisture content: Japonica rice tends to have a
2. Oryza nivara: Another wild relative of Oryza higher moisture content.
sativa, Oryza nivara, is found in India and other
parts of South Asia. It is found growing in 2. Indica Variety:
swampy areas, at edge of pond and tanks, - Non-sticky texture: Indica rice grains are less sticky
beside streams, in ditches, in or around rice when cooked, making them suitable for dishes that require
fields. separate grains like biryani.
- Long grains: Indica rice has longer grains compared
3. Oryza glumaepatula: This wild rice species is to Japonica rice.
native to Central and South America. It is - Nutty flavor: It has a nuttier and more aromatic flavor.
considered a distant relative of Oryza sativa but - Lower moisture content: Indica rice generally has a
shares some genetic similarities. It is found in lower moisture content.
deep and sometimes in flowing water.
These characteristics can vary within each subspecies and
may also be influenced by factors such as growing
conditions, soil type, and cultivation practices.
REPORTED BY:
MR. ANGELO A. TAGUPA
&
MR. LYDIO LUZANO FUERTES JR.