Do parthenocarpic fruits perpetuate the plant species? How?

Question

i can't really understand parthenocarpy. How do these kind of fruits develop, and how could they reproduce without seeds. I don't understand the concept of spores either. So far, they're the only structures I know for asexual reproduction. Does this relate to parthenocarpy? Please, help. Thank you very much... I will appreciate if you give an answer and an explanation why, of course.

Answer 1

PARTHENOCARPY

In botany and horticulture, parthenocarpy (literally meaning virgin fruit) is the natural or artificially induced production of fruit without fertilization of ovules. The fruit is therefore seedless. Parthenocarpy occasionally occurs as a mutation in nature, but it is usually considered a defect, as the plant can no longer sexually reproduce, but may propagate by asexual means.

However, parthenocarpy of some fruits on a plant may be of value. Up to 20% of the fruits of wild parsnip are parthenocarpic. The seedless wild parsnip fruit are preferred by certain herbivores so serve as a "decoy defense" against seed predation. Utah juniper has a similar defense against bird feeding.Being able to produce seedless fruit when pollination is unsuccessful may be an advantage to a plant because it provides food for the plant's seed dispersers. Without a fruit crop, the seed dispersing animals may starve or migrate.

In some plants, such as seedless watermelon, pollination or other stimulation is required for parthenocarpy. This is termed stimulative parthenocarpy. Banana exhibits stimulative parthenocarpy because it is a triploid -meaning it is the result of a diploid and a tetriploid parent and therefore cannot produce seeds. Plants that do not require pollination or other stimulation to produce parthenocarpic fruit have vegetative parthenocarpy. Cucumber is an example of vegetative parthenocarpy.

Plants moved from one area of the world to another may not always be accompanied by their pollinating partner and the lack of pollinators has spurred human cultivation of parthenocarpic varieties. Some parthenocarpic varieties have been developed as genetically modified organisms.

SEEDLESS FRUITS

Seedless fruits is something of an oxymoron, as fruits are usually defined in a botanical sense as mature ovaries containing seeds. Among the widely grown seedless fruits are grapes, numerous Citrus fruits (oranges, lemons, limes, etc.), and bananas. Seedless watermelons have only recently been developed by a Japanese professor Kihara. Seedless fruits are commercially valuable as seeds are considered a nuisance by consumers and seedless fruits are easier to eat and thus preferred over otherwise similar seeded fruits. Most commercially produced seedless fruits have been developed from plants whose fruits normally contain numerous relatively large hard seeds that are distributed throughout the flesh of the fruit; there would be little commercial benefit to a seedless peach or apple.

Seedless fruits can develop in one of two ways: either the fruit develops without any fertilization (parthenocarpy), or pollination triggers fruit development but the ovules or embryos abort without producing mature seeds (stenospermocarpy). Seedless fruits of banana and watermelon are produced on triploid plants, whose three sets of chromosomes prevent meiosis from taking place and thus do not produce fertile gametes. Such plants can arise by spontaneous mutation or by hybridization between diploid and tetraploid individuals of the same or different species. Some species produce seedless fruit if not pollinated but seeded fruit if pollination occurs, e.g. pineapple and cucumber.

A common question is how, if they do not produce seeds, such plants can be propagated. In most cases the plants are propagated vegetatively from cuttings, by grafting, or in the case of bananas, from "pups" (offsets that grow near the parent plant). In such cases the resulting plants are genetically identical clones. Oddly enough, seedless watermelons are grown from seeds. These seeds are produced by crossing diploid and tetraploid lines of watermelon, with the resulting seeds producing sterile triploid plants. Fruit development is triggered by pollination and these plants must be grown alongside a diploid strain to provide pollen.

One disadvantage of most seedless crops is that, as genetically identical clones, a pest or disease that can harm one individual can harm every individual of that clone. For example, the vast majority of commercially produced bananas come from a single clone, the 'Cavendish' cultivar, which is currently threatened worldwide by a newly discovered fungal disease to which it is highly susceptible.




Commercial Importance

Seedlessness is a very desirable trait in edible fruit with hard seeds such as pineapple, banana, orange and grapefruit. Parthenocarpy is also desirable in fruit crops that may be difficult to pollinate or fertilize, such as tomato and summer squash. In dioecious species, such as persimmon, parthenocarpy increases fruit production because staminate trees do not need to be planted to provide pollen. Parthencarpy is undesirable in nut crops, such as pistachio, where the seed is the edible part. Horticulturists have selected and propagated parthenocarpic cultivars of many plants, including fig, cactus pear (Opuntia), breadfruit and eggplant. Some plants, such as pineapple, produce seedless fruits when a single cultivar is grown because they are self-infertile. Some cucumbers produce seedless fruit if pollinators are excluded. Strange as it seems, seedless watermelon is propagated by seed. The seeds are produced by crossing a diploid parent with a tetraploid parent to produce triploid seeds.

When sprayed on flowers, any of the plant hormones, gibberellin, auxin and cytokinin, can often stimulate the development of parthenocarpic fruit. This is termed artificial parthenocarpy. Plant hormones are seldom used commercially to produce parthenocarpic fruit. Home gardeners sometimes spray their tomatoes with an auxin to assure fruit production.

Some parthenocarpic cultivars have been developed as genetically modified organisms.

Some parthenocarpic cultivars are of ancient origin. The oldest known cultivated plant is a parthenocarpic fig first grown at least 11,200 years ago.

In some climates, normally seeded pear cultivars will produce mainly seedless fruit.

Misconceptions
Most commercial seedless grape cultivars, such as 'Thompson Seedless' are not seedless because of parthenocarpy, but because of stenospermocarpy.
Parthenocarpy is sometimes claimed to be the equivalent of parthenogenesis in animals. That is incorrect because parthenogenesis is a method of asexual reproduction, and parthenocarpy is not, except in rare cases such as pineapple. The plant equivalent of parthenogenesis is apomixis.

SPORES

In biology, a spore is a reproductive structure that is adapted for dispersion and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many plants, algae, fungi and some protozoans.

Spores are usually haploid and unicellular and are produced by meiosis in the sporophyte. Once conditions are favorable, the spore can develop into a new organism using mitotic division, producing a multicellular gametophyte, which will eventually go on to produce gametes. Two gametes fuse to create a new sporophyte. This cycle is known as alternation of generations. Haploid spores produced by mitosis (known as mitospores) are used by many fungi for asexual reproduction.

It is useful to contrast spores with gametes: spores are the units of asexual reproduction as a single spore develops into a new organism; gametes are the units of sexual reproduction as two gametes need to fuse to create a new organism.

The term spore may also refer to the dormant stage of some bacteria or archaea, however these are more correctly known as endospores and are not truly spores in the sense discussed in this article. The term can also be loosely applied to some animal resting stages. Fungi that produce spores are known as sporogenous, and those that do not are asporogenous.

The term derives from the ancient Greek word for seed.

Classification of spores

By function
Diaspores are dispersal units of fungi, mosses, ferns, fern allies, and some other plants. In fungi, chlamydospores are thick-walled resting spores, and zygospores are thick-walled resting spores (hypnozygotes) of zygomycetous fungi which are produced by sexual gametocystogamy and can give rise to a conidiophore ("zygosporangium") with asexual conidiospores.

By spore-producing structure
In fungi and fungus-like organisms, spores are often classified by the structure in which meiosis and spore production takes place, such as a telium, ascus, basidium, or oogonium, which produce teliospore, ascospores, basidiospores, and oospores, respectively. Since fungi are often classified according to their spore-producing structures, these spores are often characteristic of a particular taxon of the fungi, such as Ascomycota or Basidiomycota.

By origin during life cycle
Meiospores are the product of meiosis (the critical cytogenetic stage of sexual reproduction), meaning that they are haploid, and will give rise to a haploid daughter cell(s) or a haploid individual. An example is the parent of gametophytes of the higher vascular plants (angiosperms and gymnosperms)—the microspores (give rise to pollen) and megaspores (give rise to ovules) found in flowers and cones; these plants accomplish dispersal by means of seeds.

A mitospore (conidium, conidiospore) is an asexually produced propagule, the result of mitosis. Most fungi produce mitospores. Mitosporic fungi are also known as anamophic fungi (compare teleomorph or deuteromycetes).


By motility
Spores can be differentiated by whether they can move or not. Zoospore can move by means of one or more flagellum and can be found in some algae and fungi. Aplanospore cannot move, but may potentially grow flagella. Autospore cannot move and do not have the potential to ever develop any flagella. Ballistospore are actively discharged from the body of a fungal fruit (such as a mushroom). Statismospore are not actively discharged from the fungal fruit body, similarly to a puffball.

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Answer 2

In the superstore, fruits are usually selected far too soon. Some are rocks, many are wrong. Some of the fresh vegetables are right (zucchini, onions, garlic, lettuce, greens, and a few others) so I'd have to go with vegetables.