hybrid seed production

History of hybrid seed

                Hybrid seed began with maize in the 1920s, and became extended to vegetables and flowers; and more recently, rice and some forage crops.

What are Hybrid Seeds?

—  hybrid seeds are a variety of seeds which are created by cross-pollination of plants.

—  Hybrid seeds are produced from naturally out-breeding crops, from which inbred lines are produced by repeated self-pollination.

—  The established inbred lines are crossed to produce first generations (F1) hybrid seeds.

What is heterosis?

—  The phenomenon of heterosis, also referred to as 'hybrid vigor,'underlies much of the improvement in crop yields achieved in the twentieth century.

—  Heterosis can result in a large increase in yield over the inbred lines.

—  The precise basis of heterosis is still unclear, but epistasis and over-dominance are thought to be involved.

—  Epistasis is the interaction between different genes

—  Over-dominance is a condition where the heterozygotes (genes represented by two different versions) are superior to either homozygotes (gene represented by the same versions).

—  The F1 hybrid seed is heterozygous in many genes.

Why use Hybrid Seeds?

—  Better Yield

—  Greater Uniformity

—  Disease Resistance.

Many cucurbit genes for disease resistance are dominant, and F1 hybrids with resistance to some diseases may be developed from crosses with only one resistant parent.

Production of Melon hybrid seed

—  Inbred lines without serious depression of vigor have been developed for melon and watermelon.

—  Some cucurbit inbred lines, however, have reduced vigor and yield.

—  Inbreeding may be defined as any system of mating that will lead to an increase in

  homozygosity.

Hand emasculation and hand pollination

—  This technique is frequently used for melon hybrid seed production.

—  In this species, andromonoecious lines are common and they must be emasculated and hand pollinated if used as the female parent for producing hybrid seed.

—  This technique is applicable for limited scale production, since lot of trained labour are required for pollen collection and hand pollination.

Watermelon flowers

Male flower 

Female flower 

Hand emasculation and pollination by insects

—  The male flowers from female lines are pinched off day before of anthesis regularly.

—  The Male and female parents are grown in adjacent rows in the field in 1:3 or 1:4 ratio.

—  The fruit set on female lines are of hybrid and harvested for seed extraction.

Pollination by insects

Use of genetic male sterility system

—  Genetic male sterility system has been utilized for commercial hybrid production in muskmelon.

—  The genetic male sterility in muskmelon is controlled by single recessive gene (msms).

—  For hybrid seed production, the male sterile line is used as female parent.

—  The female and male are grown in 4:1 ratio.

—  It is also advised that female line seedling should be raised in polythene bags and transplanted at flower appearance in order to avoid the fertile plants in female rows.

—  The pollination is done by honey bees and 1 to 2 medium sizes hives are good enough to ensure the good pollination and fruit set at female row.

—  The male sterile line is maintained in heterozygous form by crossing with maintainer line under adequate isolation distance or under cover.

Use of gynoecious sex form

—  The gynoecious sex form has been commercially exploited in hybrid seed production of cucubits.

—  For hybrid seed production female and male rows are planted in 4:1 ratio.

—  The female (seed parent) bear only female flowers and pollination is done by insect (honeybee).

—  The parental lines i.e. male parent maintained by selfing.

—  Rouge out undesirable plants before contamination take place.

—  The female lines i.e. gynoecious lines maintained by inducing the staminate flower through the sprays of silver nitrate 200 ppm at two to four true leaf stage and then selfing is carried out.

—  It was observed that 10-11 male flowers appear per 100 nodes.

Hybrid seed production through chemical sex expression

—  Hybrid seed can also be produced in cucurbits by the application of chemicals for attaining the sex of cucurbits.

—  Specific chemicals are known to induce femaleness and maleness as desired.

—  The spraying of ethrel (2-choloro-ethyl­phosphonic acid) 200-300 ppm at two and four true leaf stage and another at flowering is useful for inducing the pistilate flowers successively.

—  The row of male parent is grown side by the side of female and natural cross pollination is allowed.

—  In the absence of insect, hand pollination is possible when two sexes are separate.

Isolation

Melons are highly cross pollinated crop. Hence, the minimum recommended isolation distance for pure seed production is 1000m

Roguing

v  Thorough roguing is carried out in male parent before pollination.

Roguing in female parent is done at all stages  of crop growth on the basis of phenotypic characters

Harvesting

v  Normally the fruits mature after 30-35 days of pollination and the seeds turn from brown to black.

v  Fully mature fruits can be confirmed when the tendrils have withered on the node bearing the fruit.

v  There is a change in the colour of fruit part touching the ground from green to yellow and on thumping the metallic sound of rind changes into ruffled dull or dead sound.

Seed extraction

v  The flesh along with seeds is removed   from the rind and kept for fermentation for one day.

v  The seeds, which settle down, will be separated from juice and flesh and washed thoroughly with water.

v  Machines are also used for large-scale seed extraction.

v  Yield: 225 –280 kg/ha.

Seed drying

Soon after extraction seeds are first dried in shade by spreading on a mounted nylon net then under sunlight. Seed moisture should be brought down to 7% for open storage and to 6% for moisture proof storage.