SOURCE SEED (BS, FS & IS )

PRODUCTION OF MAIZE

Jiban Shrestha

Scientists (Plant Breeding and Genetics)

Nepal Agricultural Research CouncilNational Maize Research Program, Rampur, Chitwan, Nepal

Biology of the maize plant:

The maize plant has separate male and female flowers

(Monoecious Plant). The location of the tassel (male

flower) at the top of a relatively tall plant and its

separation from the female flower promotes cross-

pollination between plants. One tassel may produce up to

25 million pollen grains.

How to produce maize seed:

To maintain the genetic purity and characteristics of a

variety cross-pollination between different maize

varieties must be prevented. Isolating the seed

production field from other maize fields helps achieve this.

Seeda link between plant generation

a carrier of gene

a technology most transportable, storable, and

functional unit

Quality seeds central to agricultural production and

productivity

a source of all food with plant origin

Seed is fertilized mature ovule covered by a

protective coat/coats which is viable and can

germinate under favorable environment conditions

Types of seed

1. Nucleus Seed

2. Breeder Seed

3. Foundation Seed

4. Improved Seed

Nucleus Seed

Nucleus seed is also called progenitor

of breeder seed. There is direct

involvement of breeder in nucleus seed

production. Selection is done with

certain rules. Nucleus seed is produced

in very less quantity.

Breeder Seed

The progeny of nucleus seed.

Produced at one place only in the control of breeders

through positive selection process with very strong rouging.

Golden yellow tag is used

To maintain the highest level of purity, the breeder's

seed plot should be small and manageable.

Acceptable Standard deviation can be ±0.7sfor

quantitative traits of plants and ears.

Coefficient variation can be ±3% for qualitative traits

of plants and ears

Ways/Methods of Breeder Seed Production:

1. Isolated mass selection plot

Parental seed should be planted in isolation to obtain

about 8000 plants. The entire field can be stratified in grids of

16 plants each. Before pollen shed, about half of plants in each

grid which do not fit the description of variety are detasseled.

Before harvest 2-3 of most acceptable plants in each grid are

selected and tagged. At harvest ears from only one of the tagged

plants that are acceptable color and kernel texture is selected

from each grid. A total of 500 ears are selected in this manner

from the parental seed. Ears of plants that were not detasseled

and that fit well the definition of the variety provide the breeder

seed to produce the foundation seed. Ears from the detasseled

plants may harvested for commercial gain.

2. Half sib crossing block

It requires isolation and can be

initiated in the first generation of breeder seed increase.

The 500 ears selected from the bulk seed increased are

shelled separately, and planted as individual female

entries in a half sib crossing block, in which every two

female rows are flanked by one male row. Male row

consists of a balanced mixture of an equal amount of

seed from each ear. Before anther dehiscence all plants

in the female rows are detasselled. Roughing of the off

types and the undesirable plants can take place in male

row to leave no less than 70 of the tassels intact to

ensure an adequate pollen supply.

Approximately half the numbers of female rows are selected as

most desirable and representative of the variety. Selection of the

family is aided by the reference male row at its side, which

represents the mean of the variety. From each selected female

row or family, 2-3 of the best ears from the best plants are

selected to recover approximately 500 ears as parents for the next

increases of the breeder seed. Rests of the ears from the selected

female rows are harvested as breeder seed for the production of

foundation seed. Thus the system is maintained.

Because of the utmost important of maintaining the uniformity

of the breeder seed, the seed of origin, it is imperative that this be

done by the breeder in one location only, and the soil condition

and management should be uniform.

Foundation SeedThe progeny of breeder seed.

Produced through negative selection process with strong

rouging.

white tag is used.

Certification process used for the foundation seed.

Up to 10-15% of the off-type plants can be rogued

before flowering. Roguing for ear and seed traits is done

at or after the harvest.

Acceptable Standard deviaton can be ±1.55sfor

quantitative traits of plants and ears.

Coefficient variation can be ±5% for qualitative traits

of plants and ears

Ways of Foundation seed production

The second seed increase serves to

produce foundation seed. Foundation seed is

obtained by planting the breeder seed in

isolation. Selection is not possible nor

desirable at this stage, but of off types plants

should be rouged before pollen shed, and

more pollination is allowed. In any event the

area of production should be uniform to

minimize undesirable variation.

Improved Seed

The progeny of foundation seed.

Produced with medium rouging.

white tag with blue border is used.

Certification and Truthful label process used for the improved

seed.

Up to 5% of the off-type plants rogued before flowering.

Roguing for the ear and seed traits at or after the harvest.

Acceptable Standard deviaton can be 1.96sfor quantitative

traits of plants and ears.

Coefficient variation can be ±8% for qualitative traits of

plants and ears

Ways of Improved Seed Production

In the third seed increased improved seed is produced

from foundation seed in the same manner as described

above. Again selection is neither necessary nor desirable,

but roughing is essential. An appropriate area to produce

sufficient seed for current demand, plus necessary carry

over stock, is planted with foundation seed in isolation

and open pollination is allowed. Obvious off types plants

are roughed before dehiscence to maintain the integrity of

the variety.

Because of the greatly increased area needed to produce

the necessary quantity of seed at this phase it will be

necessary to use several different locations, farmer

participation as contract growers is essential. The close

collaboration of the research staff and the farmers

during variety evaluation and verification trials is

especially helpful here since it will allow the

researchers to identify the most reliable farmers for this

valuable function. The integrity and the quality of seed

for the commercial planting will depend on the integrity

and quality of these farmers, the producers of improved

seed.

Isolating a seed production field:

Isolation of a seed crop can be done in four ways:

1. By space or distance - maintain a distance of at

least 200 meters between the seed crop and any

other maize field.

2. By time - plant your seed crop 20 – 25 days

earlier or later than neighboring maize fields.

3. By certified seed barrier (Boarder rows)– a barrier of

genetically pure seed of the same variety may be planted

within the isolation distance of the seed production field.

For example:

Area (ha) of the seed field No. of

boarder rows

of the Male

Parent

4 8 12 16

Isolation Distance in meter

200 190 180 170 1

150 140 130 120 5

50 40 30 20 13

4. By natural barriers – seed production plots can be

established on land isolated by natural or artificial

forests.

Distance and time isolation are most commonly used.

The goal is to have no other maize variety shedding

pollen nearby when the seed production field is

flowering.

Wind may carry pollen further than 300 meters. Thus,

if there are constant strong winds in one particular

direction, the distance to the next maize field should be

at least 400 meters.

How to select a suitable field:

• Check with neighbors when and where they will

plant their maize so that you can select a field that

is isolated.

• Choose a field where no maize has been grown

during the previous year to reduce the possibility

that last year’s maize crop may germinate and

cross-pollinate your seed maize.

• Farming communities may want to produce the

seed of one variety for the entire community in one

single field. (eg. CBSP).

How to manage your seed production field:

• Prepare the soil in your field at least two weeks prior

to planting. If there are any grains from previous

maize crops left in the soil, they may germinate in

these two weeks and you should remove them when

you plant your maize seed crop.

• If possible, plant your maize seed crop early.

• Use 10 - 15 % less plant population than maize grain

production plot.

• Planting in straight rows will help facilitate various

seed production operations.

• Remove weeds in time.

Rouging

During the season, carefully examine your maize seedcrop:

Plants that look very different ( taller, very dwarf,diseased, weeds) or flower much earlier or later than themajority of plants in the field. These plants are calledoff-types and they should be removed (Rouged out)before pollen shedding starts.

If off-type maize plants are detasseled, seeds from suchplants should not be used.

Number of

plants per

hectare

Row width in cm

50 60 70 75

Spacing between plants (in the same row in cm)

35,000 57 48 41 38

40,000 50 40 35 33

45,000 44 35 31 30

50,000 40 30 28 26

55,000 36 37 25 24

60,000 33 25 22 21

65,000 31 22 20 19

70,000 28 21 19 18

Row width and spacing between the plants in the

row according to the desired density

In seed production, 75cm × 30 cm spacing or 45,333 plant population/ha or Seed rate-17kg/ha is needed

Standards for maintaining varietal uniformity

Maize seed should meet the following standards

Minimum field standard

Minimum crop standard

Minimum seed standard

Minimum field standard

Land requirement:Free fromVolunteer Plants

-Crop rotation to minimize volunteer maize

plants and reduce the need for roguing.

Maintaining isolation distance or time

Isolating a seed production field:

1.By space or distance

2.Bytime-plant your seed crop 20-25 days earlier

or later than neighboring maize fields.-Silking

period should not coincide with corn in near by

fields

Minimum number of field inspections

First inspection-Before flowering

Verification of seed source, isolation distance and

suggestion for rouging.

Second inspection-After complete flowering

Counting, field certification/rejection

Third inspection-Cob inspection at threshing

floor

Minimum crop standard off-type plants

Less than 10-15 & 5% off-type plants in foundation and

improved seed respectively

No any designated diseases and weed plants

S. N. Parameters

Standards

Foundation

Seed

Improved Seed

1 Pure seed (Minimum) 98.0 % 98.0 %

2 Inert matter (Maximum) 2.0 % 2.0 %

3 Other crops seed (Maximum) 5/kg 10/kg

4 Other varieties seed

(Maximum)

10/kg 20/kg

5 Weed seed (Maximum) 0 0

6 Germination (Minimum) 85 % 85 %

7 Moisture (Maximum) 12.0 % 12.0 %

Minimum Seed Standard

Seeds hould be obtained from reliable source and seed replacement

should be done every year to ensure good quality seed production

Thank you