Breeding: Perennial Tetraploid Watermelon

[oxbowfarm]

Very interesting paper just got brought to the attention of the Plant Breeding for Permaculture Facebook group. Very relevant to Joseph's perennial Watermelon project. Basically indicates that you can create interspecies polyploids using approach grafting and then inducing shoot initiation at the graft union. There apparently is nuclear genome transfer at the cellular level in the graft region which creates polyploid cells, then you need to trick those cells into initiating a new shoot. In terms of this melon project, I'd try attempting some grafts with the diploids while you are creating your tetraploids, multiple approaches to the same goal?

[Joseph Lofthouse]

oxbowfarm: Thanks. I attempted inter-species grafts of seedlings a month ago. It wasn't successful. I'll plan on doing approach grafting of older plants next season. I attempted the grafts working under the speculation that inter-species grafting would make inter-species pollinations more likely due to RNA and chemicals shared between the rootstock and the scion.

[philagardener]

That is a very interesting paper; so far the effect has been observed between tobacco species (which regenerate quite easily in tissue culture) but there is potential.

[raymondo]

I recall reading that someone (Michurin? apples and pears?) doing interspecies grafts used older rootstock on which was grafted very young scion stock, or perhaps it was vice versa. I wonder of briony/watermelon grafts might work similarly.

[Joseph Lofthouse]

raymondo: Thanks! Bryony has a perennial root, and is a very cold hardy plant in this area. It starts growing months before it is safe to plant watermelon outdoors. So it might make sense to graft watermelon seedlings onto year old bryony plants. How about using that particular graft as a means of producing an earlier crop??? I wonder what would happen if watermelons were grafted -- after danger of frost -- onto those huge tap roots that have already been actively growing for months? Followed by pruning away the bryony foliage. Huge amounts of energy could be devoted to growing watermelon vines in June instead of taking months to grow a big enough root system to finally start sending out vines in August. One problem I foresee with this scheme is the need for constant pruning of the root to prevent bryony shoots from re-sprouting. I also wonder how much poison would be transmitted through the watermelon vines to the fruits.

[nicollas]

If i remember correctly, there are more chances that the rootstock influence seeds than the fruits on the vines, so it could be a very useful (though labor intensive) procedure. To best have chances to influence seeds with hope to transmit perennialty from rootstock you should prune all but the last 2-3 leaves of the scion every weeks or so, like Michurin was doing in his Mentor grafting technique. From scientific literature it seems that sometimes the changes appear when selfing the plant obtained from sowing the seeds taken on the scion of the grafted plant.

[raymondo]

Aug 3, 2014 21:36:58 GMT -5 oxbowfarm said:

Very interesting paper just got brought to the attention of the Plant Breeding for Permaculture Facebook group. Very relevant to Joseph's perennial Watermelon project. Basically indicates that you can create interspecies polyploids using approach grafting and then inducing shoot initiation at the graft union. There apparently is nuclear genome transfer at the cellular level in the graft region which creates polyploid cells, then you need to trick those cells into initiating a new shoot. In terms of this melon project, I'd try attempting some grafts with the diploids while you are creating your tetraploids, multiple approaches to the same goal?

oxbowfarm: I wasn't able to read the entire article, only the abstract. How did they go about getting shoots from the graft region?

[nicollas]

Full paper here : libgen.org/scimag/get.php?doi=10.1038%2Fnature13291

[raymondo]

Thanks nicollas.

[Joseph Lofthouse]

I didn't remove the tetraploid flowers reliably in the diploid/tetraploid crossing block. But the plants grew and produced melons. Here's what that looked like. I'm looking forward to planting these next year to see if any seedless triploids show up.



Unfortunately, one of the diploid melons wasn't as striped as I would have liked. Might make it hard to tell which seeded and which is seedless just by looking. Perhaps the shapes will be different enough to tell. Since stripes are dominant, a striped fruit showing up in the tetraploid row is harvested as "seedless".



Overall, it was a bad year for watermelons. Progress on the perennial part of this project amounted to growing out a larger population of bryony close to home so that I don't have to go searching for flowers, roots, or seeds. I have them on hand now. I attempted to pollinate melon flowers with bryonia pollen, but none of the fruits grew.

[Joseph Lofthouse]

I planted the seed today from the Seedless Watermelon part of this project... Growing them in the greenhouse for a few weeks.

I saved sibling group seeds from 5 fruits in the crossing block. 2 diploids, and 3 presumably tetrapoids. I'm intending to keep records and make labels this year to try to definitively answer whether any of these are polyploids.

I'm intending to plant the seeds of the round non-striped melon separately. It doesn't have the traits I want for the diploid mother.

I have plants from a more genetically diverse strain of B. alba growing in the garden.

[avishay]

Hi Joseph. Amazing project.
Triploid melons fail to make meiosis, and therefor cannot make pollen (If they could, we wouldn't need a pollinator to induce fruit development in the seedless melon fields).
You can scan your plants for the presence of pollen in the male flowers, and that can give you a good early hint for their ploidity.
Good luck!

[Joseph Lofthouse]

So here's what the seedless watermelon attempt looked like before I planted them this spring.



The pot all the way to the right is the diploid Charleston Gray that I started out with.
The pot in the middle is the suspected tetraploid of Charleston Gray with possibly some triploids mixed in.
The pot on the left is from the striped diploid line. (Possibly contains some triploids).

I planted the seeds fruit-to-hill.

There was one batch of seeds from the suspected tetrapoid in which the leaves were not as large as expected, so I planted that one in a separate field. One of the round diploid fruits wasn't striped, so I likewise planted that in other field. I'm interested in seeing if any seedless melons show up, but they didn't conform to specs so they basically got consigned to the food-only field.

[Joseph Lofthouse]

I've been watching the plantings of the diploid watermelon and the possibly tetraploid, and measuring leaf sizes to see if I can get an early indication of what I might expect... Some of the results were hard to interpret in the greenhouse, so I made small plantings in 3 different fields.

I can't discern any plants among the possibly tetra population that I think might be seedless triploids.

However, among the diploid/triploid population there are large-leaved plants and small-leaved plants. Possible that the large-leaved might be seedless triploids?

Anxiously waiting...

Sibling group: Diploid mother, possibly selfed, or possibly pollinated with pollen from tetraploid plants.

[Joseph Lofthouse]

A few watermelon fruits are starting to grow.

Here's what the parents of the cross looked like. The oblong light green fruit is the presumed tetraploid, and is the mother of the cross. The presumed pollen donor produced the striped diploid fruit.



Here's what one of the offspring looks like: Shape mid-way between that of the two parents. It is lightly striped. Perhaps this will be a seedless melon?