Stenospermocarpy
Encyclopedia
Stenospermocarpy is the biological mechanism that produces seedlessness in some fruits, notably many table grapes. In stenospermocarpic fruits, normal pollination
Pollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...

 and fertilization are still required to ensure that the fruit 'sets', i.e. continues to develop on the plant; however subsequent abortion of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 that began growing following fertilization leads to a near seedless condition. The remains of the undeveloped seed are visible in the fruit.

The fruit of seedless grapes is smaller than normal because the seeds produce the plant hormone
Plant hormone
Plant hormones are chemicals that regulate plant growth, which, in the UK, are termed 'plant growth substances'. Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved...

 gibberellin
Gibberellin
Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence....

, which causes fruit enlargement. Most commercial seedless grapes are sprayed with gibberellin
Gibberellin
Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence....

 to increase the size of the fruit and also to make the fruit clusters less tightly packed. A new cultivar, 'Melissa', has naturally larger fruit so does not require gibberellin sprays.

Grape breeders have developed some new seedless grape cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...

s by using the embryo rescue technique. Before the tiny embryo aborts, it is removed from the developing fruit and grown in tissue culture
Tissue culture
Tissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar...

 until it is large enough to survive on its own. Embryo rescue allows the crossing of two seedless grape cultivars.

Seedless grape cultivars

Seedless grapes are divided into white, red and black types based roughly on fruit color. The most popular seedless grape is known in the United States as 'Thompson Seedless', but was originally known as 'Sultana'. It is believed to be of ancient origin. It is considered a white grape, but is actually a pale green. Other white cultivars are 'Perlette', 'Menindee Seedless', 'Interlaken', 'Himrod', 'Romulanus', 'Lakemont', 'Fayez', and 'Remailey Seedless.' The most popular red seedless in the U.S. is 'Flame Seedless'. Other red cultivars are 'Crimson Seedless', 'Ruby Seedless', 'Suffolk Red', 'Saturn' and 'Pink Reliance'. Some black cultivars are 'Black Beauty', 'Black Monukka', 'Concord Seedless', 'Glenora' and 'Thomcord.'

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