Formation of fruits and seeds:

Simultaneously with the development of embryo and endosperm, ovary enlarges in size. Sepals, petals, stamens, style and stigma fall off and ovary changes into fruit.

Ovary wall changes into pericarp (fruit wall) which may or may not be differentiated into epicarp, mesocarp and endocarp.

Pericarp is initially green in colour and on ripening becomes orange, red, purple, yellow etc.

Each ovule in the ovary also enlarges in size.

Outer integument becomes thick and hard outer seed coat, called testa.

The inner integument changes into thin, inner seed coat, called tegmen.

Thus small, sot and succulent ovule becomes dry and hard seed after fertilization.

 

Parthenocarpy:

Mostly, the fruits are formed ater fertilization, but there are some species in which fruits develop without fertilization.

This is called parthenocarpy and such fruits are called parthenocarpic fruits, e.g. Banana.

Parthenocarpic fruits are without seeds and hence are preferred by consumers.

Parthenocarpy can be induced through application of growth hormones like gibberellins, e.g. seedless grapes.

 

Apomixis and polyembryony:

Seeds are the products of fertilization. In some species of family Asteraceae and some grasses seeds are produced without fertilization. This is called apomixis and such seeds are called apomictic seeds.

Apomixis is a form of asexual reproduction that mimics sexual reproduction.

In some species, diploid egg cell is formed without reduction division (meiosis) and it develops into an embryo without fertilisation and thus apomictic seeds can be formed.

In many Citrus varieties, some of the nucellar cells near the embryo sac start dividing, protrude into the embryo sac and develop into the embryos.

Ovule in such species contain many embryos, this is called polyembryony.

More and more Indian farmers have started using hybrid seeds for increase in the productivity and other benefits.

However, there is one problem with hybrid seeds, that is, they are to be produced every year and the production is costly.

If the seeds collected from hybrids are sown, the characters segregate in the progeny.

The hybrid seeds are expensive for farmers to buy every year.

If these hybrids are made into apomictics, there will be no segregation of characters in the progeny.

Farmers can keep on using hybid seeds year after year and need not buy hybrid seeds every year.

Active research is going on in many laboratoies around the world to understand the genetics of apomixis and to transfer the apomictic genes into hybid varieties.