Seedlessness in grapes is not due to triploidy although that seems to
be a common misconception. Most seedless grape cultivars are not even
parthenocarpic, as are most other species or cultivars that produce
seedless fruit. Parthenocarpic species or cultivars produce fruit
without fertilization so the fruit are truly seedless. 'Black
Corinth'is considered a parthenocarpic grape.

Most seedless grapes are stenospermocarpic, which means the seeds
start to develop after normal pollination and fertilization but abort
before maturity. The remains of the aborted seed(s), called seed
traces, can be seen in the "seedless" fruit.

Grape breeders now use tissue culture to prevent the tiny embryos from
aborting. This technique is called embryo rescue. It allows two
seedless grapes to be crossed and produce viable offspring. Embryo
rescue had been a major reason why there are so many new seedless
grape cultivars.

References

Table Grape Berry Growth and Development: A Review
http://cetulare.ucdavis.edu/pub/Grape0302.PDF

SEEDLESS GRAPE: Use of biotechnology to find new seedless cultivars
http://www.biotecnologia.com.br/bio/10_gi.htm

Trio of New Seedless Grapes on the Way to Consumers
http://www.ars.usda.gov/is/pr/1999/990618.htm



ose (Sean Houtman) wrote in message ...



More often when plants have triploids, the result is no seeds in the fruit.
Examples are seedless grapes and seedless bananas.

Sean

Most seedless grapes are stenospermocarpic, which means the seeds start to
develop after normal pollination and fertilization but abort before maturity.
The remains of the aborted seed(s), called seed traces, can be seen in the
"seedless" fruit.
Grape breeders now use tissue culture to prevent the tiny embryos from
aborting. This technique is called embryo rescue. It allows two seedless grapes
to be crossed and produce viable offspring. Embryo rescue had been a major
reason why there are so many new seedless grape cultivars.

Will it work with bananas? Somebody told me all the banana plants in the world
are dying of an incurable disease. And of course the commercial bananas are
seedless.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)

In article , (Iris Cohen) wrote:
Most seedless grapes are stenospermocarpic, which means the seeds start to
develop after normal pollination and fertilization but abort before maturity.
The remains of the aborted seed(s), called seed traces, can be seen in the
"seedless" fruit.
Grape breeders now use tissue culture to prevent the tiny embryos from
aborting. This technique is called embryo rescue. It allows two seedless grapes
to be crossed and produce viable offspring. Embryo rescue had been a major
reason why there are so many new seedless grape cultivars.

Will it work with bananas? Somebody told me all the banana plants in the world
are dying of an incurable disease. And of course the commercial bananas are
seedless.

Seedless bananas are sterile because they are triploids, so I would be
surprised if embryo rescue would work. (But I'm always happy to be
surprised. :-)


Cheers, Phred.

--
LID

I'm not aware that any banana species have stenospermocarpy. If genes
for stenospermocarpy can be identified in other species, maybe bananas
could be genetically engineered to be stenospermocarpic.

The prediction that existing cultivars of seedless banana will be
extinct within a decade unless they are genetically engineered for
disease resistance is just a prediction. Researchers may come up with
new pesticides that can control the serious pests and diseases
threatening the seedless banana crop.

There is probably a political motive for the dire prediction because
many nations are strongly opposed to genetically engineered crops. The
story came from a Belgian scientist and banana expert, Dr. Emile
Frison. Dr. Frison is the Director of the International Network for
the Improvement of Banana and Plantain. He favors genetically
engineered crops even though banana producers don't:
http://www.cbc.ca/stories/2003/01/16...bananas_030116
http://www.ipgri.cgiar.org/institute/press270103.htm

It would be an interesting test case for nations that have banned all
genetically engineered crops if Dr. Frison proves correct and the
only seedless bananas available in ten years are genetically
engineered cultivars.


David R. Hershey



(Iris Cohen) wrote in message ...
Most seedless grapes are stenospermocarpic, which means the seeds start to
develop after normal pollination and fertilization but abort before maturity.
The remains of the aborted seed(s), called seed traces, can be seen in the
"seedless" fruit.
Grape breeders now use tissue culture to prevent the tiny embryos from
aborting. This technique is called embryo rescue. It allows two seedless grapes
to be crossed and produce viable offspring. Embryo rescue had been a major
reason why there are so many new seedless grape cultivars.

Will it work with bananas? Somebody told me all the banana plants in the world
are dying of an incurable disease. And of course the commercial bananas are
seedless.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)

I sent David's posting to my favorite grape geneticist and got this
reply (posted with her permission):

In article ,
David Hershey wrote:
Seedlessness in grapes is not due to triploidy although that seems to
be a common misconception. Most seedless grape cultivars are not even
parthenocarpic, as are most other species or cultivars that produce
seedless fruit. Parthenocarpic species or cultivars produce fruit
without fertilization so the fruit are truly seedless. 'Black
Corinth'is considered a parthenocarpic grape.

Most seedless grapes are stenospermocarpic, which means the seeds
start to develop after normal pollination and fertilization but abort
before maturity. The remains of the aborted seed(s), called seed
traces, can be seen in the "seedless" fruit.

There are apparently two stenospermocarpic mutations which account for
almost all seedless grape cultivars. There is no reason to believe that
this exhausts the possibilities, since the cultivars in the two groups are
either clones of each other or in some cases parent/offspring pairs. Many
of these clones have been propagated so long that enough somatic mutations
have accumulated to consider them unique individuals, not just sports.

For more information about these groups, see "Simple Sequence Repeat
Analysis of a Clonally Propogated Species: A Tool for Managing a Grape
Germplasm Collection", by GS Dangl, ML Mendum, BH Prins, MA Walker, CP
Meredith, and CJ Simon, GENOME 44: 432-438 2001. Don't know if it's
available on the web or not.


Grape breeders now use tissue culture to prevent the tiny embryos from
aborting. This technique is called embryo rescue. It allows two
seedless grapes to be crossed and produce viable offspring. Embryo
rescue had been a major reason why there are so many new seedless
grape cultivars.

The other reason is the institution of several breeding programs, at UCD
and among some commercial companies. It helps that DNA fingerprinting
(available through the Meredith lab previously, shortly to be offered
through the Foundation Plant Material Service when Bud finishes making the
transition) can now positively identify patented individuals, making it
much harder to steal the fruits of a breeding program, if you'll parden the
pun.

Previously, grape varieties were identified through ampelography: sight
identification through leaf and cluster characteristics, mostly.
Unfortunately, grapes show a wide variation in these characteristics
depending on climate and other conditions, and there are darned few really
good ampelographers out there. (The aforementioned Andy Walker is one, and
there's a guy in France with an unspellable name, Jean-Micheaux Borsechot,
or something similar.)

The DNA fingerprinting is a lot cheaper, a lot surer, and much, much easier
to learn.

One nice thing about this thread is that I learned two new words. Since
my spouse also likes new words, I thought I'd try them out on him:

Me: Here's a new word for you: ampelography.
Him: Hmm. "Enough writing"?
Me: Bah! How about stenospermocarpic then?
Him: [long pause] "Male note taker with sore wrists"?

While I have not seen an actual report of a chromosome count, it is widely
reported that 'Thompson Seedless', the best-known, historically most important
seedless grape in the US, and from which a major percentage of the fresh grape
market, virtually all raisins, and virtually all processed grapes are produced
in this country, is triploid. Is it the odd exception to stenospermocarpy, or
are such reports in error, I wonder?

Me: Here's a new word for you: ampelography.
Him: Hmm. "Enough writing"?
Me: Bah! How about stenospermocarpic then?
Him: [long pause] "Male note taker with sore wrists"?

lolrog. Love it.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)

It is a widespread misconception that 'Thompson Seedless' grape is
triploid. I have even seen that misconception in biology textbooks.
Several university websites also say 'Thompson Seedless' grape is
triploid:
http://www.biology.arizona.edu/cell_...iosis/04q.html
http://www.bol.ucla.edu/~bredelin/RDGenes/week3.html
http://fybio.bio.usyd.edu.au/vle/L1/...ems/Unit09.htm

However, they are in error.

The University of California seedless grape review link I posted
earlier mentions that seedlessness in grapes in caused mainly by
stenospermocarpy. It does not even mention the term triploid:

Table Grape Berry Growth and Development: A Review:
http://cetulare.ucdavis.edu/pub/Grape0302.PDF

'Thompson Seedless' grape cannot be triploid (3n) because it has been
used as a parent in breeding of other seedless grape cultivars.
Triploids cannot produce viable pollen or eggs because meiosis
requires an even ploidy number such as 2n or 4n. 'Himrod' seedless
grape is a cross between 'Ontario' and 'Thompson Seedless':

Seedless grapes:
http://www.nysaes.cornell.edu/hort/f...abletext3.html

Embryo rescue would not work with 'Thompson Seedless' if it was
triploid. However, 'Thompson Seedless' has been used as both male and
female parent in embryo rescue research:

http://www.actahort.org/books/528/528_99.htm


David R. Hershey




(MMMavocado) wrote in message ...
While I have not seen an actual report of a chromosome count, it is widely
reported that 'Thompson Seedless', the best-known, historically most important
seedless grape in the US, and from which a major percentage of the fresh grape
market, virtually all raisins, and virtually all processed grapes are produced
in this country, is triploid. Is it the odd exception to stenospermocarpy, or
are such reports in error, I wonder?

David Hershey wrote:
It is a widespread misconception that 'Thompson Seedless' grape is
triploid. I have even seen that misconception in biology textbooks.
Several university websites also say 'Thompson Seedless' grape is
triploid:
http://www.biology.arizona.edu/cell_...iosis/04q.html
http://www.bol.ucla.edu/~bredelin/RDGenes/week3.html
http://fybio.bio.usyd.edu.au/vle/L1/...fTestAnswers/L
+ivingSystems/Unit09.htm

However, they are in error.

The University of California seedless grape review link I posted
earlier mentions that seedlessness in grapes in caused mainly by
stenospermocarpy. It does not even mention the term triploid:

Table Grape Berry Growth and Development: A Review:
http://cetulare.ucdavis.edu/pub/Grape0302.PDF

'Thompson Seedless' grape cannot be triploid (3n) because it has
been used as a parent in breeding of other seedless grape cultivars.
Triploids cannot produce viable pollen or eggs because meiosis
requires an even ploidy number such as 2n or 4n.

I do not know what the situation is in this grape cultivar, but it is
not generally true that triploid plants are incapable of parenthood.
In fact, there are biologists who study the so-called 'triploid
bridge' that enables (a low rate of) gene transfer in wild
populations between diploid and tetraploid 'species'.

The following sort of situation has been observed (for example in
dandelions). During meiosis in the triploid, two of the three
complete sets of chromosomes pair with each other, and the remaining
set of chromosomes end up in varying numbers in each of the two
products of that first meiotic division. In effect, the gametes from
the triploid contain numbers of chromosomes that cover the entire
range of numbers between 1n (half the diploid number) and 2n (half
the tetraploid number). It is thus possible for a triploid to produce
a very small number of offspring either from crossing with a diploid
or from crossing with a tetraploid, or even (a much lower number of
offspring) from crossing with a similar triploid (if pollen
self-incompatibility in the stigma and style don't prevent this).

My favourite 'Lexia' raisins occasionally contain a seed, and I have
even managed to germinate these, but have not yet produced a strong
plant that doesn't get mildew. I had assumed that 'Lexia' was a
triploid grape that is also parthenocarpic (since the fruit don't
abort even if there are no mature seeds), but I don't actually know
if this is the case.

==
Nadia Talent / .
Department of Botany / University of Toronto
and Centre for Biodiversity and Conservation Biology / Royal Ontario Museum

I was speaking about cultivated plants where triploidy is used to
prevent seed formation, such as in triploid watermelons, triploid
marigolds and a hypothetical triploid grape. Even such triploids may
rarely produce a seed but they are seedless for practical purposes.

Technically, meiosis requires an even chromosome number. A triploid
dandelion producing a mix of 1n to 2n gametes doesn't really fit the
definition of meiosis. Meiosis is defined as a cell division that
produces four cells, each with half the chromosome number of the
beginning cell.

I don't know how the idea that 'Thompson Seedless' was triploid got
started. Assuming a seedless fruit is triploid is not a good bet. Most
commercial seedless fruit are not triploid. They are seedless for
other reasons such as lack of pollination or lack of compatible
pollen.

The assumption that 'Lexia' grape is triploid and parthenocarpic
because most 'Lexia' raisins don't have seeds may be a bad assumption.
'Lexia' is one of many synonyms for 'Muscat of Alexandria' or
'Muscatel' grape:
http://www.psgrill.net/Wine/Varietal...er/muscat.html

Raisins made from Muscat grapes often have their seeds removed during
processing:
http://www.internationalrecipesonlin...ionary.pl?5637
http://www.ams.usda.gov/standards/raisin.pdf

Therefore, 'Lexia' may not be a seedless grape. Occasional seeds in
'Lexia' raisins may just be seeds not removed during processing.


David R. Hershey


(Graeme Hirst) wrote in message ...
David Hershey wrote:
It is a widespread misconception that 'Thompson Seedless' grape is
triploid. I have even seen that misconception in biology textbooks.
Several university websites also say 'Thompson Seedless' grape is
triploid:
http://www.biology.arizona.edu/cell_...iosis/04q.html
http://www.bol.ucla.edu/~bredelin/RDGenes/week3.html
http://fybio.bio.usyd.edu.au/vle/L1/...fTestAnswers/L
+ivingSystems/Unit09.htm

However, they are in error.

The University of California seedless grape review link I posted
earlier mentions that seedlessness in grapes in caused mainly by
stenospermocarpy. It does not even mention the term triploid:

Table Grape Berry Growth and Development: A Review:
http://cetulare.ucdavis.edu/pub/Grape0302.PDF

'Thompson Seedless' grape cannot be triploid (3n) because it has
been used as a parent in breeding of other seedless grape cultivars.
Triploids cannot produce viable pollen or eggs because meiosis
requires an even ploidy number such as 2n or 4n.

I do not know what the situation is in this grape cultivar, but it is
not generally true that triploid plants are incapable of parenthood.
In fact, there are biologists who study the so-called 'triploid
bridge' that enables (a low rate of) gene transfer in wild
populations between diploid and tetraploid 'species'.

The following sort of situation has been observed (for example in
dandelions). During meiosis in the triploid, two of the three
complete sets of chromosomes pair with each other, and the remaining
set of chromosomes end up in varying numbers in each of the two
products of that first meiotic division. In effect, the gametes from
the triploid contain numbers of chromosomes that cover the entire
range of numbers between 1n (half the diploid number) and 2n (half
the tetraploid number). It is thus possible for a triploid to produce
a very small number of offspring either from crossing with a diploid
or from crossing with a tetraploid, or even (a much lower number of
offspring) from crossing with a similar triploid (if pollen
self-incompatibility in the stigma and style don't prevent this).

My favourite 'Lexia' raisins occasionally contain a seed, and I have
even managed to germinate these, but have not yet produced a strong
plant that doesn't get mildew. I had assumed that 'Lexia' was a
triploid grape that is also parthenocarpic (since the fruit don't
abort even if there are no mature seeds), but I don't actually know
if this is the case.

==
Nadia Talent / .
Department of Botany / University of Toronto
and Centre for Biodiversity and Conservation Biology / Royal Ontario Museum