Oryza sativa, commonly known as rice, is a grass species cultivated extensively as a grain worldwide. There are two major subspecies of domesticated rice: indica varieties, which are nonsticky and commonly grown in lowlands; and japonica varieties, which are sticky and commonly grown in upland or temperate areas. Rice is a staple food in many parts of the world and is high in carbohydrates but low in fat and protein. It is also rich in various vitamins and minerals. Rice cultivation began in China and spread throughout Asia and later to other parts of the world. There have been efforts to develop rice varieties with improved traits like drought, salt, and disease tolerance to address environmental and agricultural

2. Kingdom: Plantae
(unranked): Angiosperms
(unranked): Monocots
(unranked): Commelinids
Order: Poales
Family: Poaceae
Genus: Oryza
Species: O. sativa
Classification :
Oryza sativa is a grasswith a genome consisting of 430Mb across
12 chromosomes

3. Classification:
Oryza sativa contains two major subspecies:
1. The sticky, short-grained japonica or sinica variety, and
2. the nonsticky, long grained indica variety.
Japonica varieties are usually cultivated in dry fields, in temperate East Asia, upland
areas of Southeast Asia, and high elevations in South Asia,
while indica varieties are mainly lowland rice, grown mostly submerged, throughout
tropical Asia.
Rice occurs in a variety of colors, including: white, brown, black, purple, and red
Black rice (also known as purple rice) is a range of rice types, some of which are
glutinous rice. Varieties include Indonesian black rice and Thai jasmine black rice.
A third subspecies, which is broad-grained and thrives under tropical conditions, was
identified based on morphology and initially called javanica, but is now known
as tropical japonica.
Examples of this variety include the medium-grain 'Tinawon' and 'Unoy' cultivars,
which are grown in the high-elevation rice terraces of the Cordillera Mountains of
northern Luzon, Philippines.

4. •Debates on the origins of the domesticated rice are numerous.
•In 2011, genetic evidence shows that all forms of Asian rice,
both indica and japonica, spring from a single domestication
that occurred 8,200–13,500 years ago in China of the wild rice Oryza
rufipogon.
• A 2012 study, through a map of rice genome variation, indicated that
the domestication of rice occurred in the Pearl River valley region of
China.
•From East Asia, rice was spread to South and Southeast Asia.
•Before this research, the commonly accepted view, based on
archaeological evidence, is that rice was first domesticated in the
region of the Yangtze River valley in China

5. Beginning in China and the surrounding areas, its
cultivation spread throughout Sri Lanka, and India.
It was then passed onto Greece and areas of the
Mediterranean. Rice spread throughout Southern
Europe and to some of North Africa.
From Europe rice was brought to the New World.
From Protugal it was brought into Brazil and from
Spain to Central and South America.
Journey of Rice

6. Nutrient content of Rice
STAPLE RDA
Rice
(white)[B]
Component (per 100g
portion)
Amount Amount
Water (g) 3000 12
Energy (kJ) 1528
Protein (g) 50 7.1
Fat (g) 0.66
Carbohydrates (g) 130 80
Fiber (g) 30 1.3
Sugar (g) 0.12
Calcium (mg) 1000 28
Iron (mg) 8 0.8

7. Magnesium (mg) 400 25
Phosphorus (mg) 700 115
Potassium (mg) 4700 115
Sodium (mg) 1500 5
Zinc (mg) 11 1.09
Copper (mg) 0.9 0.22
Manganese (mg) 2.3 1.09
Selenium (μg) 55 15.1
Vitamin C (mg) 90 0

8. Thiamin (B1)(mg) 1.2 0.07
Riboflavin (B2)(mg) 1.3 0.05
Niacin (B3) (mg) 16 1.6
Pantothenic acid (B5)
(mg)
5 1.01
Vitamin B6 (mg) 1.3 0.16
Folate Total (B9) (μg) 400 8
Vitamin A (IU) 5000 0
Vitamin E, alpha-
tocopherol (mg)
15 0.11
Vitamin K1 (μg) 120 0.1
Beta-carotene (μg) 10500 0

10. Fibrous Root System
The fibrous root system is made
up of thin, stringy roots that all
have about the same diameter.
These roots branch several
times and form a complex mat
under the plant that binds to the
upper soil layers. Fibrous roots
can be found in monocots such
as grasses

11. Stem
THE RICE STEM HAS A STRUCTURE SIMILAR
TO OTHER MONOCOT GRASSES.
Another name for the stem of the rice plant
is the CULM.
The culm consists of several NODES
spaced apart by INTERNODES 1 cm apart
near the base, and further apart towards the
top of the rice plant.
The internodal length can reach 10-30 cm at
the formation of the panicle from the last
internode.

12. LEAF SHEATH Leaf Sheath an elongated, cylindrical structure
that encloses younger parts of the shoot.
Its major function is to protect younger shoots
inside of it and to support the whole plant, which
explains why there are very few chloroplasts
found in the sheath mesophyll.
Leaf Blade flat, elongated, and ribbon like--the
"leafy" part of the leaf
it is usually longer than the sheath
its major function is to perform photosynthesis
Collar a white band at the junction of the blade
and the sheath
Ligule
triangular, papery scale located inside the blade
it looks like a continuation of the sheath
it is absent in some species
Auricle a pair of hairy, sickle-shaped
appendages located in the junction of the collar
and the sheath
it is absent in some species
Collar Auricle

13. Flower structure

14. •There are 6 stamens in each rice flower.
•Each stamen is composed of an anther and a filamen
•An anther includes 4 elongated sacs where pollen
grains are stored.
•The filament is a long, thin stem that holds the anthe
•The vascular bundles in the filament transport
nutrients and water to the anther.
Anthers Pollens
Stamen

15. The carpel consists of the female parts of the rice
flower the Stigma, the style ,and the ovary.
The stigma receives pollen grains, which will then
be transported into the ovary,
where fertilization occurs.
Carpel

16. Lodicule
On a rainy day, or when the temperature is too low or too high
,the lodicules shrink , causing the spikelet to close.
When the floral parts mature, the lodicules will swell and open
the spikelet to expose the mature floral parts.
Lemma and Palea
These are hardened, modified stems that protect the floral
organs.
The lemma is relatively larger than the palea.
When the spikelet is closed, the lemma partly encloses the
palea.
The pointed end on top of the lemma is called an awn.
Sterile lemma
The sterile lemmas are much smaller in size than the lemma,
and they do not bear flower, hence their name "sterile".
Pedicel
A pedicel branches from every node on the secondary rachis
and a flower is produced on top of it.

17. Panicle development occurs in the acropetal
direction for the primary branches.
However, the terminal spikelet matures first
which is basipetal development.
Panicle
Endosperm
Embryosac
The rice grain, otherwise known as the fruit of the
rice plant, develops at the end of a panicle in
a cluster of spikelets.
The outer coating serves as protection to the fruit
that lies inside.

19. Rainfall
Temperature
Rice requires high temperature above 20 °C (68 °F) but not more than 35
to 40 °C (95 to 104 °F). Optimum temperature is around 30 °C (Tmax) and
20 °C (Tmin).
Solar radiation
The amount of solar radiation received during 45 days after harvest
determines final crop output.
Atmospheric water vapor
High water vapor content (in humid tropics) subjects unusual stress
which favors the spread of fungal and bacterial diseases.
Wind
Light wind transports CO2 to the leaf canopy but strong wind cause
severe damage and may lead to sterility (due to pollen dehydration,
spikelet sterility, and abortive endosperms).[

20. Golden Rice was one of seven winners
of the 2015 Patents for
Humanity Awards by the United States
Patent and Trademark Office.
As of 2016, it is still in development

21. Drought-tolerant rice
Drought represents a significant environmental stress for rice production, with 19–
23 million hectares of rainfed rice production in South and South East Asia often at
risk.
Under drought conditions, without sufficient water to afford them the ability to obtain
the required levels of nutrients from the soil, conventional commercial rice varieties
can be severely affected – for example, yield losses as high as 40% have affected
some parts of India, with resulting losses of around US$800 million annually.
The International Rice Research Institute conducts research into developing
drought-tolerant rice varieties, including the varieties 5411 and Sookha dhan,
currently being employed by farmers in the Philippines and Nepal respectively.
 In addition, in 2013 the Japanese National Institute for Agrobiological Sciences led
a team which successfully inserted the DEEPER ROOTING 1 (DRO1) gene, from the
Philippine upland rice variety Kinandang Patong, into the popular commercial rice
variety IR64, giving rise to a far deeper root system in the resulting plants.
 This facilitates an improved ability for the rice plant to derive its required nutrients
in times of drought via accessing deeper layers of soil, a feature demonstrated by
trials which saw the IR64 + DRO1 rice yields drop by 10% under moderate drought
conditions, compared to 60% for the unmodified IR64 variety.

22. Salt-tolerant rice
 Soil salinity poses a major threat to rice crop productivity, particularly along low-
lying coastal areas during the dry season.
For example, roughly 1 million hectares of the coastal areas of Bangladesh are
affected by saline soils.
 These high concentrations of salt can severely affect rice plants’
normal physiology, especially during early stages of growth, and as such farmers are
often forced to abandon these otherwise potentially usable areas.
Progress has been made, however, in developing rice varieties capable of tolerating
such conditions; the hybrid created from the cross between the commercial rice
variety IR56 and the wild rice species Oryza coarctata is one example.
 O. coarctata is capable of successful growth in soils with double the limit of salinity
of normal varieties, but lacks the ability to produce edible rice.
 Developed by the International Rice Research Institute, the hybrid variety can
utilise specialised leaf glands that allow for the removal of salt into the atmosphere.
 It was initially produced from one successful embryo out of 34,000 crosses
between the two species; this was then backcrossed to IR56 with the aim of
preserving the genes responsible for salt tolerance that were inherited
from O.coarctata.

23. Environment-friendly rice
Producing rice in paddies is harmful for the environment
due to the release of methane by methanogenic bacteria.
These bacteria live in the anaerobic waterlogged soil, and
live off nutrients released by rice roots.
Researchers have recently reported in Nature that putting
the barley gene SUSIBA2 into rice creates a shift in biomass
production from root to shoot (above ground tissue becomes
larger, while below ground tissue is reduced), decreasing the
methanogen population, and resulting in a reduction of
methane emissions of up to 97%.
Apart from this environmental benefit, the modification also
increases the amount of rice grains by 43%, which makes it
useful tool in feeding a growing world population

24. Long Grain Brown Rice Medium Grain Brown Rice
Short Grain Brown Rice
Sweet Brown Rice Wehani® Rice Brown Basmati Rice
Himalayan Red Rice Colusari Red Rice Purple Thai Rice Purple Thai Rice

25. Physiological aspects of onion

26. Onion (Allium cepa L.) is an important bulb crop grown
world wide.
Onion (Allium cepa) is a popular vegetable grown for its
pungent bulbs and flavorful leaves
Onion (Allium cepa L) is extremely important vegetable crop
not only for internal consumption but also as highest foreign
exchange earner among the fruits and vegetables.
It occupies an area of 695.1 thousand ha, with production of
9,248.4 thousand tons.
It is an important crop in all condiment and used for
flavouring the food, both at mature and immature bulb stages
besides being used as salad and pickles.
To lesser extent, it is used by processing industry for
dehydration in the form of onion flakes and powder, which are
in great demand in the world market.
Onion(Allium cepa L.)
Introduction

27.  The genus Allium is in the monocot order Asparagales,
family Alliaceae, and includes various economically
important and cultivated species
 The distinctive flavor or odor of the genus is produced
when plant tissues are bruised or cut and the enzyme
alliinase hydrolyzes S alk(en)yl cysteine sulfoxide
precursors to form volatile sulfur compounds
 Onion, garlic, and their relatives, although primarily
grown for food, are also used in traditional medicine,
including the treatment of chicken pox, the common
cold, influenza etc. Antimicrobial characteristics of the
alliums are likely the result of sulfur compounds.

28. Medicinal properties of onions
Raw Onions
Nutritional value per 100 g (3.5 oz)
Energy 166 kJ (40 kcal)
Carbohydrates 9.34 g
- Sugars 4.24 g
- Dietary fiber 1.7 g
Fat 0.1 g
- saturated 0.042 g
-
monounsaturated
0.013 g
- polyunsaturated 0.017 g
Protein 1.1 g
Water 89.11 g
Vitamin A equiv. 0 μg (0%)
Thiamine (vit. B1) 0.046 mg (4%)
Riboflavin (vit. B2) 0.027 mg (2%)
Niacin (vit. B3) 0.116 mg (1%)
Vitamin B6 0.12 mg (9%)
Folate (vit. B9) 19 μg (5%)
Vitamin B12 0 μg (0%)
Vitamin C 7.4 mg (9%)
Vitamin E 0.02 mg (0%)
Vitamin K 0.4 μg (0%)
Calcium 23 mg (2%)
Iron 0.21 mg (2%)
Magnesium 0.129 mg (0%)
Phosphorus 29 mg (4%)
Potassium 146 mg (3%)
Sodium 4 mg (0%)
Zinc 0.17 mg (2%)

29. History
Onion have been part of our food from as far back as
3200 B.C. and are cited as important food staples in the
Bible and Koran. The Greeks and Romans wrote about
onion 400 - 300 B.C., and onion was popular in northern
Europe at the start of the Middle Ages. Its medicinal
properties were reviewed in the Indian medical treatise
Charaka Samhita nearly 2,000 years ago.
Cultivation
The bulb onion exists only in cultivation and likely
originated in central Asia. It is now cultivated worldwide
and is commonly found in vegetable markets of most
countries. Local phenotypes vary in shape (tall, round, or
flat), color (white, yellow, pink, or red), firmness,
pungency, dormancy, and solids content.

30. Onions produced for dehydration have a much higher solids
content than the sweet, fresh market type.
Onion is a diploid (2n=2x=16) herbaceous biennial; i.e., it
requires two years per generation. The bulb is a modified stem with
fibrous roots and fleshy leaves. Onion forms about 15 leaves per
growing season but rarely has more than 10 living leaves at any one
time. The plant loses four to five leaves during the growing season to
natural senescence and death. Premature leaf death is associated
with disease or other damage. Bulb formation in onion is affected by
temperature and photoperiod. Onion populations have been
classified on the basis of the length of daylight required to initiate
bulb formation; short day populations need about 12 hr of daylight
and long day types require up to 16 hr. Onion is an insect-pollinated
crop. The seed is formed within a three celled capsule, which usually
contains two black seeds. A cluster of capsules form in the spherical
inflorescence (umbel) at the terminal end of the hollow stalk (scape)
which elongates from the biennial bulb.

31. World scenario
India is the 2nd largest producer of onion, in the world
next only to China but the productivity of onion in India is
very low i.e. 13.3 tons/ ha as compared to China and other
countries like U.S.A, Egypt and Turkey.
Botany/Anatomy of Onion
The onion is a familiar plant with, perhaps, an unfamiliar
anatomy.
 In onion plant, anatomy and physiology are inextricably linked.
The form of an onion plant, whether overall or microscopic, is
intimately related to its function or physiology.
Many complex physiological processes come into play as an
onion plant lives and grows.
The common onion (Allium cepa) is a biennial with large bulbs
that are usually single.

32. Scientific name : Allium cepa L.
Order : Liliales
Family : Liliaceae
Habitat : Probably native of southwest
Asia but is widely cultivated
throughout the world.
An aromatic, common vegetable with round, hollow leaves
and an underground bulb.
Cotyledons : Two.
Leaves : Stipules, Petiole
Blade - Long, round, hollow,
Stem leaves
Stems : Long.
Flower head : At the ends of the stems.
Flowers : Ovary ,Calyx, Perianth,Sepals
Petals, Stamens,Anthers

33. Seeds : Small.
Roots : Fibrous.
Life cycle : Biennial. Seed is planted from
February to September and harvested
2-6 months later depending on variety.
Climate : Cool temperate.
Prefer temperatures from 13-240C.
Soil : Prefers medium to heavy friable clay
loams that are deep and well drained
with a pH of 6-6.5, but they will grow
on a wide range of soils.

34. STAT
E
JA
N
FE
B
MA
R
AP
R
MA
Y
JUN JUL AU
G
SEP OC
T
NO
V
DE
C
MS
Guj
Bihar
Kar
AP
MP
Raj
Har
UP
Harvesting season of crop in leading states
Lean season Peak season

35. Physiology :
1) Optimum temperature for growth 13-240C.
2) Frost tolerant.
3) Cool temperatures before bulbs are formed improves
yields.
4) Prefer dry conditions at harvest.
5) Flowering induced by temperatures below 100C when
seedlings are greater than 6 mm diameter.
6) Bulb formation initiated by day lengths of 12-16 hours
and bulb growth is faster at higher temperatures.

36. Morphology of Onion
Roots
Onion have a fibrous root system consisting of a fairly dense
mass of smaller individual roots. The onion has a fibrous type of root
system. Onion roots carry out functions typical of many plants. They
have an internal microscopic structure of conducting tissue, termed
xylem and phloem, that serves both as structural support and to
transport water and nutrients throughout the plant.
Fibrous root system of onion, 3.5 months old.An onion 8 weeks after the seed was planted.

37. Early root Development.--The onion develops a primary
root which, under very favorable conditions, may reach
a length of 3 to 4 inches 10 days after the seed is
planted. In the meantime the cotyledon comes from the
ground in the form of a closed loop. By the time the
first foliage leaf emerges from the base of the cotyledon,
several new roots make their appearance near the base
of the stem.
TABLE- RATE OF ROOT GROWTH OF ONION
Age Lateral spread Working depth Maximum depth,
days inches inches inches
55 4 10 12
106 12 20 27
133 12 32 39

38. Stem
The onion stem is considerably reduced. The stem is very
small and insignificant during vegetative growth. After
vernalization at temperatures below 10°C, the stem elongates
rapidly, eventually producing compound umbels. But despite its
different form, the onion stem's physiology and function is like
the stems of other plants in that it conducts water and nutrients
to other parts of the plant.
Leaves
The green leaves above the bulb are hollow and arise
sequentially from the meristem at the innermost point at the
base of the bulb.They are highly modified leaves, but still leaves
nevertheless. Those modified bulb leaves serve as nutrient
storage structures for the plant. At the top of the onion's
underground parts , the roots and bulb , is a continuation of the
onion's set of leaves.

39. The onion's above-ground leaves, though, are
tubular and green. Their physiological role is to absorb
light energy and carry out photosynthesis. This
physiological process manufactures the sugars that
nourish the onion plant, including the bulbous leaves
below.
Flowers and Seeds
Although the gardener who grows onions may not be
interested in the onion plant's flowers or seeds, the onion is a
flower and seed-producing plant. It generates flowers that
botanists classify as umbels. An umbel is a flower head of
multiple individual flowers that resembles an umbrella.
Onion flowers, once pollinated, develop and mature into
seeds. When the onion's seeds encounter a suitable
environment, they germinate, mature, flower and fruit and
thereby continue the onion plant's life cycle.

40. The bulb is composed of concentric, fleshy, enlarged leaf
bases or scales. The outer leaf bases lose moisture and become
scaly and the inner leaves generally thicken as bulbs develop.
Cultivars differ substantially with respect to the threshold
daylength required for bulbing. Other factors such as temperature
may interact with daylength to modify the bulbing response. In all
cultivars, bulbing is accelerated with increasing temperature.
Temperature extremes not only affect the rate of bulbing, but also
affect the bulb shape. Thick and elongated necks are common in
plants exposed to 6° or lower.
Bolting in Onion
Bolting has been reported to be related to the length of day.
However, long days do not induce reproductive growth but tend to
accelerate development of the seedstalk once it has been initiated
by vernalization. Temperature has a major role in inducing bolting.
Bulbing in Onion

41. The onion crop cycle
The onion cycle has 10 development stages, from planting to bulb
maturity. Learning to recognize each stage is essential to
implement an efficient crop management program
Seed
Seed in soil after planting
Pre-emergence
Underground germination
before emergence of the
cotyledon.
After the underground
germination, the
cotyledon appears. It
looks like an arch.
First leaf
When the first leaf emerges [1],
the plant is still in the flag stage.
Cotyledon fall
After a progessive drying out and the
emergence of leaves 2 and 3, the cotyledon falls.
Germination

42. Bulb forming
The bulb starts to form; the 2nd and 3rd
leaves dry out while leaves 8 to 13 appear;
the plant is at its maximum development.
Bulb thickening
Beginning of the regression of the vegetative
phase.
Laying down plant
The vegetative phase is over; The leaves lay
down on the soil and start to dry out. The
bulb has almost reached its final size
Bulb maturity
The tunic is finished. The leaves and the
neck are completely dry. When
harvested, the bulb, completely closed,
is seperated from the aerial part.

43. Figure 1
Figure 3
Figure 2
Figure 4
Pre-Bulb Growth Stages
1 . Radical and flag leaf emergence (10–30 days post seeding) Fig.1
2 . One to two true leaves (30–50 days)
3 . Three to four leaves (50–70 days) Fig.2
4 . Five to seven leaves (70–90 days) Fig.3
5 . Eight to 12 leaves, bulb initiation (90–110 days) Fig.4
Growth Stages of Onion

44. Figure
5
Figure
6 Figure
7 Figure 8
Post-Bulb Growth Stages
1 . Bulb diameter of 2.5 to 4.0 cm (110–130 days)
2 . Bulb diameter of 4.0 to 7.5 cm (130–150 days) Fig.5
3 . Bulb diameter greater than 7.5 cm (150–170 days.)
4 . Bulb enlargement complete, greater than 50% cropped to dry
down (more than 170 days.) Fig.6
5. Bulb will then produce a scape or seed stalk Fig.7
6. Umbel stage [Fig. 8] which produces true seed after fertilization.

45. Physiological aspects of Onion
 Yield of Onion crops depends on relationships between
their growth and development rates and environmental
variables, like temperature and day length
Fundamental Determinants of yield
The attainment of high yield of high quality is the end
results of growth and development. Well established
principles determine the yield of onions. The yield of a crop
is determined by:
1. The quality of light absorbed by its leaves while
harvestable dry matter is being produced
 The quantity of light absorbed depends on the quantity
of light radiating on the field, the percentage absorbed
by the leaves, & the duration of growth of yield –
bearing components.

46.  Therefore, a high yielding crop must produce a leaf
canopy with a high percentage absorption of incident
light during a season of high solar irrradiation.
 The longer the duration over which such a leaf canopy is
transferring photosynthate to harvestable material, the
higher is the yield.
The leaf canopy development is controlled by
physiological responses to environmental conditions.
2.The efficiency with which the absorbed light is
converted by photosynthesis into sucrose
It is affected by the temperature and water status of the
leaves.
If temperatures are above or below the optimum for
photosynthesis, efficiency will be reduced.
Similarly ,if leaves are water stressed to the extent that

47. Stomata are closed & the diffusive resistance to CO2
entry is increased,then this too will reduce photosynthetic
efficiency
Therefore photosynthesis & growth the crop must have
adequate supplies of water and mineral nutrients &
suitable tempereture.
3.The proportion of photosynthetic output transferred
to the harvested fraction of the plant
At the optimum time of harvesting 80% plant have soft
necks i.e. about 80% of the shoot weight is in the bulb.
Bulb weight will continue to increase after this stage and
the percentage of total weight in the bulb will increase.
Bulb onions ,therefore have a high harvest index
(the proportion of total yield in harvested material)

48. 4. The conversion coefficient between photosynthetic
sucrose and the biochemical constituents of the
harvested material
 The weight of dry matter stored in the structural and the
storage tissues of the plants depends primarily on
biochemical composition.
 A lower weight of lipid, protein or lignin is produced
per unit of sucrose utilized in biosynthesis than is the
case for structural or storage carbohydrates.
5.The weight loss due to respiration and decay after the
above photosynthetic and biosynthetic processes have
occurred.
The ceiling of yield reached when dry matter gains from
photosynthesis are equaled by dry matter losses due to
respiration & tissue senescence.

49. Factors influencing the yield of bulb Onions
1. Plant density 2. Sowing date 3.Cultivar
Table: The effect of plant density on bulb yield and light
interception for Onion
Plant Density( plants m-2)
25 100 400
Bulb yield
(Kg m-2 of dry matter)
0.46 0.71 1.02
Leaf Area Index during bulbing 0.82 1.5 2.3
Percentage light interception by
leaf canopy during bulbing
30.0 46.0 59.4
Maturity date 14 Aug. 2Aug. 24
July

50. Table: The effect of sowing date on bulb yield and light interception
Sowing date
15 March 21 April
Bulb yield
(Kg m-2 of dry matter)
1.04 0.73
Leaf Area Index during bulbing 3.7 1.5
Percentage light interception by leaf
canopy during bulbing
69 45

51. Leaf growth & leaf canopy development in Onion
 Leaf growth rate is strongly dependent on temperature
 For onion relative growth rate(RLGR) increases linearly
over the range 6-200C and this can be summarized by the
simple equation i.e. RLGR=0.0108( T- 6) , where RLGR is
in day -1 and T is temperature in 0 C and 6 0 C represents
the base temperature below which leaf growth ceases.
 Onion yields are strongly dependent on the percentage of
light intercepted by the leaf canopy during bulbing
 If bulb initiation occurred earlier, a lower LAI would be
achieved and high yields would be possible only by using
high plant densities,hence resulting in a small bulb size

52. The Control of Bulbing by Photoperiod and
Temperature
 The timing of bulb initiation in relation to leaf canopy
development is critical in determining yields in bulb-
forming alliums
 Garner and Allard (1920) first showed that onion s
develops bulbs in response to long photoperiods.
 Further research showed that, in a given daylength
bulbing was faster, the higher the temperature.

53. Physiology and environmental control of flowering
 Flowering is an essential prerequisite of seed production
and its importance is self evident for all but purely
vegetatively propagated alliums.
 Understanding of flowering and how it interacts with
vegetative growth and bulbing is important for
successful food crop production as well as seed
production
There is a sequence of stages in the life cycle from seed
germination to seed repining in the life cycle of onion.
Each stage of this cycle has different environmental
requirements

54. Seed -Emergence
Seedling
Juvenile plant
Post Juvenile plant
Vernalization - Devernalization
Inflorescence induced
Inflorescence initiated
Inflorescence visible
Umbel
Anthesis
Florates
Seed development
Juvenile phase
Thermo phase
Competition phase
Completion phase
Bulbils(Topsets)
Set or Bulb
Fig: Stages in the life cycle of Onion plants with reference to
flowering

55. The stages can be grouped into four broad phases :
1. Juvenile phase 2. Thermo phase
2. Competition phase 4.Completion phase
The stages within each phase have similar
environmental requirements, but different phases
have different requirements.
During the juvenile phase onions cannot be induced
to flower. They must reach a critical weight or leaf
number before they can enter the thermo phase in
which they can be induced by low temperatures to
initiate inflorescences.
Once the inflorescences are visible, the completion
phase is favored by higher temperatures than the
previous two stages.

56. Table : Temperature requirements and other important factors for
the various phases of the life cycle of Onions relevant to
inflorescence development
Stage of development(Phase)
Temperature (0C) Other important factors
Optimum Range
Germination ( Juvenile) 25 0-37 Water, aeration
Emergence( Juvenile) 20-25 3-37
13-28
( For > 70%
emergence
Water, aeration
Vegetative growth ( Juvenile) 20-25 10-35 Light, water, Nutrients,
photoperiods shorter than
for bulbing
Vernalization 7-12 2-17 In growing low N, high
soluble carbohydrates, long
photoperiods

57. Inflorescences
development within bulb
or plant
( Competition)
15-17 10-18 In growing plant
normal N, long
photoperiod
Anthesis (Completion) 25-30 15-40 Florets open in day
light
Pollination(Completion) 27 15-43 Relative humidity<
70% increases
pollen shedding
Seed
development(Completion)
25-30 15-43 500 C is lethal

58. Role of growth regulators on physiology of Onion
 Several classes of plant growth regulators affects
physiological activities of the Onion plant.
 Abscisic acid has been reported to induce senescence on
onion plant and prolonged bulb dormancy
Gibberellic acid has been reported as a anti bulbing
harmone because it stabilizes microtubules in cells. If
microtubules remain intact, cell do not increase in size &
bulbs are not formed.
IAA & kinetin promoted leaf growth in laboratory
condition and also affects carbohydrates metabolism,
stimulates bulb growth and and increases bulb
marketability after 4.5 months in storage
Maleic acid hydrazide has been used for many years as an
anti-sprouting agent when applied prior to harvest

59. Preharvest application of Maleic hydrazide - a sprouting inhibitor
Maleic hydrazide (MH) is a growth regulatory substance that
disrupts cell division ( Isenberg et al.,1974). If applied to onion
leaves while they are green and actively exporting
photosynthesis,MH is thanslocated to the shoot apex where it
prevents cell division. In stored bulbs this suppress sprout and root
growth.
The increase in cytokinin and other growth promoting substances,
and decrease in growth inhibitors associated with sprout
development does not occur
In untreated bulbs respiration rates increase rapidly as they
approach sprouting, whereas this increase is much lower in MH
treated bulbs.
A minimum concentration of 20 ppm MH at the centre of bulb is
required to reliably suppress sprout growth. The MH needs to
accumulate at the growing point when bulbs are nearly mature
and have therefore completed the cell division required to form
bulb

60. Scales and sprout leaf initials, but it must be applied while the
leaves are still green and actively translocating.
A period following spray application of at least 10 h without
rainfall is needed for MH absorbtion.
The best results of MH applied is observed when all plants in
the crop are at the same stage of development.
Physiological Changes During Onion Storage
The onion bulb is a natural food store for the plant, but it
is a living system undergoing a process of development towards
sprouting, and subjects to decay by various disease causing
organisms.
The object of safe storage is to maintain the bulb for as
long as possible, to provide a bulb which has a shelf life, after
removal from storage of several weeks to allow for transport and
marketing before deterioration, therefore knowledge of the
physiology of dormancy and the epidemiology of storage disease
indicates the requirements for long term storage.

61. The favorable conditions in store can be maintained by using the
physical principals of temperature and humidity control.
It is necessary to maintain the store temperature as low as
possible but above that causing freezing damage(-20 C) and to
exploit the high temperature dormancy of onion bulbs and to try
to maintain stores close to 300C
The physiological and pathological processes that proceeds
within a store of onion bulbs interact with the physical processes
of heat and water vapour exchange so as to mutually influence
the environment within the store.
Within time,sprouting and internal root development proceed
within the bulbs. These change bulb shape, tension the skins and
cracks skins.This will increase the conductivity of skins to water
vapour and therefore,the rate of water loss from the bulbs.
As sprouting proceeds, respiration will increase with increased
outputs of heat, carbon dioxide and water vapour by bulbs.
Bulb deterioration due to disease will also increase respiratory
outputs

62. Outside temperatures and solar radiation also influence the
rate of loss or gain of heat by conduction and radiation, and
this will be influenced by the design and insulation of store.
The onion skin has a pivotal role in the physical and
physiological processes in store as it is the main barrier to
water loss and to Co2 exchange.
A relative humidity in store around 65-70% is desirable to
maintain the skin fairly flexible and elastic.
At lower RH the skin becomes very brittle and easily cracked,
notably when skin moisture content falls below 20%.
However ,several studies have shown that the rate of loss of
water from onion bulbs does not decline progressively as
vapour pressure deficit between bulbs and atmosphere
increases.
Below an ambient RH of 75%,the lower vapour conductivity of
skin decreases ( Matos,1986) .

63. Good Agricultural Practices (GAP)
• Use of hybrid seeds
• Nutrient and water management
• Plant protection
• Weed management
• Better post harvest management