Ai có thắc mắc gì thì bỏ vô đây nha
Đi lụm về, ai rảnh xin dịch hộ:
Date: Tue Apr 30 21:08:07 2002
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Agricultural Sciences
ID: 1020142707.Ag
Message:
There are several ways that seedless fruits can arise. They are usually an
exception to the normal fertilization process. Most seedless fruits have what
is termed parthenocarpy, where fruit form without fertilization, but
pollination is sometimes required as stimulation. Seedless banana and seedless
watermelon are both triploid so cannot go through meiosis to form sperm and
eggs. Seedless watermelon development does require pollination from another
watermelon with functional pollen.
Plants with separate male and female individuals, such as persimmon, may form
seedless fruit if the female plant is not near a male plant and cannot be
pollinated.
Pineapples are seedless because they are grown in fields of one variety, and
they are self infertile, meaning they require cross-pollination to set seed.
With cross pollination, they would produce seeded fruit. Many citrus are
seedless for the same reason. The famous 'Washington Navel' orange is a
mutation and does not seem to produce seeds even if cross pollinated.
Many plants can be stimulated to produce seedless fruit by treating the flowers
with plant hormones, such as auxins, gibberellins, or cytokinins. Home tomato
growers often spray their tomato flowers with an auxin to get them to set
fruit.
Seedless grapes are not technically seedless, although they are seedless for
practical purposes. Seedless grapes are different than most seedless fruits
because the seeds initially develop but abort when they are very tiny embryos.
Thus, in seedless grapes, normal fertilization does occur. You can often see
the remains of the aborted seed in the mature fruit. Seedless grape breeders
can remove the tiny embryos before they abort and grow them in tissue culture
to produce a mature plant. This is termed embryo rescue. Seedless grapes have
what is termed stenospermocarpy.
Not all plants are prone to form seedless fruit. Seedlessness has been
exploited in plants where it occurs because it is so desirable commercially.
The underlying reason for seedless fruit appears to be that the tissues that
form the fruit are the parent tissues and can act independently from the seed.
Fruit tissue development does not always depends on successful fertilization or
seed development. Seedless grapes are normally sprayed with gibberellin to
increase the size of the seedless fruit but apparently there is enough
gibberellin or other hormones to make the seedless fruit form in the first
place even after the embryo aborts. A new seedless grape variety, 'Melissa',
does not even require the gibberellin spray to produce large fruit.
Contrary to several reports, there does seem to be an advantage to the plant to
produce seedless fruit under natural conditions. If a plant failed to produce
fruit some years because of poor weather conditions that prevented pollination,
it could lead to starvation or migration of animals that dispresed its seeds.
Therefore, producing seedless fruit could be beneficial to the plant by
maintaining the plant's seed dispersers. In pineapple, the leafy top of the
fruit can root and form a new plant. Thus, even a seedless pineapple may serve
to propagate the plant.
http://www.madsci.org/po...002/1020215334.Ag.r.html