Triploid apples

[FB.]

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Here are a random selection of pictures of apples known to be triploid, which haven't already been shown in my two previous topics.


Pictures from NFC will follow in subsequent posts (limited to four pictures per post).
Golden Delicious - a very fertile diploid widely used for breeding new varieties and has been used for producing seedling rootstocks - is included in every set of pictures to contrast with the known triploids.

What do you notice about the core and the seeds?

How many of the fine triploid varieties still being grown have produced lots of good seedlings?
Not many.

Why?
Probably because the abnormal genetics of triploids (which makes them poor pollinators of others) probably means genetic abnormalities in the offspring produced from those same triploids (abnormal pips/seeds) which would be expected to result in a very low proportion of high-quality seeds and lots of low-quality seeds.

So while a diploid might produce a full ten seeds which are all healthy in each fruit, a triploid might produce no truly healthy seeds in its fruit.
Clearly it's going to take a lot longer to produce lots of good-quality offspring from a triploid than a diploid.

So while triploids are valuable for their health, vigour and longevity (often growing where ordinary diploid apples cannot survive); triploids are not good pollinators or breeding partners.
Triploids are almost a kind of genetic dead-end.

[FB.]

[FB.]

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[FB.]

Bump up for this topic before letting it drift into the archives.

I thought a discussion of the potential for identifying triploids by visual clues (seeds, leaves, fruit, blossoms, growth habits) might appeal, but maybe there are less tree-fruit enthusiasts on here than I thought?

[Qzy]

I am quite interested in it but I really don't have the knowledge to add much to be honest!

[boundtothesoil]

I thought a discussion of the potential for identifying triploids by visual clues (seeds, leaves, fruit, blossoms, growth habits) might appeal, but maybe there are less tree-fruit enthusiasts on here than I thought?

I'm really interested in the topic, but I think that your list of visual diagnostics for triploids (in this or related posts) probably covers the subject pretty comprehensively.

Looking at the posted photos of the proven and suspected triploids, there don't seem to be (m)any that 'look' like the refined modern supermarket desert apples on sale these days. I guess this is to be expected.

In my small scale apple crossing efforts last year (2013), I included a number of crosses with Annie Elizabeth as the male parent, and all failed. However, two out of five crosses using Bramley's as female parent have produced healthy looking pips, although they are not necessarily the result of my intended male parent.

I've also decided to investigate how poor the germination and early seedling growth of open pollinated Ashmead's Kernel and Annie Elizabeth pips are, although I've only saved around 30-40 reasonable pips of each. They've already had 6 weeks in the fridge to stratify them and I'll be sowing them into pots held in a cold frame this week. I usually manage > 50% germination rates with the best diploid parents, but I'm not hopeful with these two varieties.

In the four years I've been crossing, I've only ever produced 4 seedlings from triploid varieties used as female parents, and two of these produced three cotyledon 'leaves' instead of the usual two, then died! The other two were stunted for a year or two then got chucked.

[FB.]

In the four years I've been crossing, I've only ever produced 4 seedlings from triploid varieties used as female parents, and two of these produced three cotyledon 'leaves' instead of the usual two, then died! The other two were stunted for a year or two then got chucked.

Most likely those which germinated but didn't thrive were aneuploid (in-between diploid and triploid with considerably more chromosomes than diploids but considerably less than triploid - often making a normal life difficult just as a Down's Syndrome child is aneuploid because of three copies of chromosome 21).

If we take half a diploid's chromosomes, that's 34/2 = 17.
Half a triploid's chromosomes is 51/2 = 25 or 26.

Combine diploid and triploid pollen and flower and you get 17+25 = 42 or 43 chromosomes on average. But the triploid parent could end up contributing more or less, depending on how its odd number of chromosomes managed to divide themselves.

[boundtothesoil]

Here's a link to an animated tutorial describing how a triploid situation can arise during meiosis.
It's quite long and complicated, but worth sticking with in my opinion

http://wps.pearsoncustom.com/wps/med...als/18_A02.swf

[FB.]

I'm really interested in the topic, but I think that your list of visual diagnostics for triploids (in this or related post) probably covers the subject pretty comprehensively.

Looking at the posted photos of the proven and suspected triploids, there don't seem to be (m)any that 'look' like the refined modern supermarket desert apples on the sale these days. I guess this is to be expected.

In a little while I'll post the names of the varieties in the pictures in the earlier topics.
The names might be very eye-opening and cause a number of "NO! IT CAN'T BE TRUE!" type of comments because many of those with freakish looking pips and cores are still listed as diploid and sometimes self-fertile or as good pollinators (but many also happen to be old, tough varieties and we know that a lot of old varieties are turning out to be triploid when researchers actually get around to testing them).

[FB.]

So after the two related threads:

http://www.growfruitandveg.co.uk/gra...ure_76277.html

http://www.growfruitandveg.co.uk/gra...two_76287.html

I'm going to consider the following varieties to be triploid (therefore poor pollinators of diploids) rather than diploid, in alphabet order:

Adams Pearmain
Alfriston
Annie Elizabeth
Arthur Turner
Brownlees Russet
D'Arcy Spice
Dumelow's Seedling
Ecklinville
Grenadier
Liberty
Lord Derby
Newton Wonder
Northern Greening
Peasgood's Nonsuch
Pinova
Reverend Wilks
Scotch Dumpling
White Transparent


Plus some others which weren't featured in the two topics:

Bountiful
Cockle Pippin
Cornish Gilliflower
Crawley Beauty
Emneth Early (Early Victoria)
Herring's Pippin
Howgate Wonder
Lane's Prince Albert
Laxton's Epicure
Monarch
Norfolk Beauty
Wolf River

Take a look at them in the National Fruit collection:
Search NFC

Most of them have abnormal looking cores and small or deformed pips suggestive of something not quite right such as a genetic abnormality. Combine abnormal cores and pips with notable disease resistance and/or tolerance of harsh conditions and/or attractive blossom and/or large fruit and/or mis-shapen fruit and it seems as if there's a good chance the variety might be triploid.

That's not to say that they're all definitely triploid because we'll have to wait and see if they ever get genetically tested. Some of them are probably diploid but the sample apple just happened to be an unusual one; if another apple had been chosen it might have been normal looking.

Could the abundance of triploids be telling us that "normal" apples just can't be grown on the scale humans demand without being overrun by diseases? That those with extra genetic material (triploids) are selected-for because the extra genes give them an advantage in disease resistance, vigour, survivability and longevity?

So if all the above might be triploid or otherwise genetically unusual resulting in lowered fertility, perhaps we have part of the explanation why so few apples are used in modern breeding programmes.
Breeders need to produce a lot of seeds to improve their chances of finding a good apple. So using low-fertility apples such as triploids dramatically reduces the number of good seeds and dramatically increases the time taken to produce any good quality seedlings.

A quote from the forum member "boundtothesoil" supports the case for breeders not spending too much time and effort with using triploids as parents:

"...In the four years I've been crossing, I've only ever produced 4 seedlings from triploid varieties used as female parents, and two of these produced three cotyledon 'leaves' instead of the usual two, then died! The other two were stunted for a year or two then got chucked...."

.

[orangepippin]

In 2012 Defra published research on ploidy levels in the Brogdale apple collection. This confirmed many suspected triploids, and Defra were apparently surprised at the high proportion of triploids present in the collection.

However the research was slightly flawed because they did not test the whole collection, instead they tested "A list of accessions which appeared not to be diploid following analysis of the microsatellite data was produced for confirmation through cytometric analyses."

As a result they appear not to have tested a large number of varieties that have some triploid attributes (as defined by FB) but which did not show up in their initial microsatellite analysis. However some other authorities have found genetic evidence supporting FB's list, e.g. Adam's Pearmain and Liberty.

It seems to me that the triploid condition is both a genetic and morphological state, and moreover is not a yes/no thing, but has a range of expressions.

A "full" triploid such as Bramley has all the visible characteristics and growth attributes noted by FB, and has the 3 alleles at the genetic level.

However there are some, such as Liberty and Adams Pearmain, which may be genetically triploid but don't seem to have many of the visible characteristics we associate with triploidy (Adams P. is a notably weak grower). And conversely there are also several varieties on FB's list which have all the visual characteristics of being triploids, but for which we don't yet have confirmation at the genetic level. Perhaps FB will consider contacting Defra to see if they will put some of these on their list for future testing?

[FB.]

Hi Orangepippin.

Maybe next spring we can get access to the National Fruit collection and spend a few days experimenting with the pollen from many of the varieties listed.

I would think that it would be possible to use a microscope to examine the pollen from those varieties to see:
1. How much pollen is produced.
2. What proportion of the pollen is within normal size ranges.
3. What proportion of the pollen is of a normal shape.
4. How much of the pollen germinates in a weak sugar solution.
5. Measure germination rates at three or four temperatures - e.g. 5'C, 10'C, 15'C, 20'C to examine whether some varieties have better pollen performance in cold or hot spring weather.

I would expect a triploid to produce pollen with a greater variability (in terms of the difference between the largest and smallest pollen grains) and to produce more abnormally-shaped pollen, and to produce pollen with lower germination rates (or where it looks abnormal after germination).

[FB.]

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I reckon we'd see something like this:


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[FB.]