The kids were eating a seedless watermelon today and I found a single black seed in it. I am confused.
I have a reasonable understanding of how a seedless watermelon is made. Diploid cross with Tetraploid creates a sterile Triploid. In theory all of the seeds in a seedless watermelon should abort early leaving you with those white empty non-viable seeds.
Occasionally seedless watermelons have a few normal looking black seeds like this. They are not hollow and certainly appear to be normal seeds. What is the story with these? I would love someone to explain it to me. Is it the loss or addition of a chromosome or something else entirely? How does it only occur to one or two seeds in every few watermelons?
I assume they are viable, but can someone confirm this please? If they are viable, what would be needed to pollinate them (diploid, tetraploid, self pollen)?
Idk but my curious son (10 years old) wants to know as well so he threw 2 of those black seeds from seedless watermelons into a pot and these are them…
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Thanks @Courtney, now I know they are viable!
If possible can you please update us as your son’s two plants grow. Let us know if they flower and if they set fruit or if it aborts please? Do you grow any other type of watermelon this year (if not we will know if they need a pollinator or if they are self fertile)?
It is winter here, so I plan to save the seed I have until spring. I normally grow some diploid (seeded) watermelons and plan to grow them again, so they should act as pollinators if my plant does grow.
Hopefully someone with a lot of knowledge can chime in and explain this.
I will try to keep them alive and see what will happen. I am in NJ for this week but will return at the end of this week. One other one that I have picture of is my Sugar Baby, growing in pots.
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I have 1 melon on each plant. There lots of flowers on both plants but only 1 melon/plant coming. They are very small so I don’t know if they will abort yet.
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I can perhaps shed a bit of light on the “seed” in a seedless watermelon. At the pachytene pairing stage of cell division, a triploid cell does not have enough chromosomes to pair properly. Under some conditions, the cell will double making it hexaploid, then undergo meiosis to produce a triploid embryo. If that embryo is fertilized by normal haploid pollen, the result is a tetraploid seed which is capable of growing and reproducing. There is an alternative where the triploid cell instead of doubling to hexaploid can lose a set of chromosomes making it diploid. It can then go through normal seed formation resulting in a diploid watermelon seed.
I simplified this a ton. Hopefully a plant geneticist won’t read it and call me on the details. I do happen to know the details. 
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Thanks @Fusion_power!
I have so many questions and wish I knew more. What are the chances of each of those scenarios happening? Is one more likely than another? What are the possible ploidy levels of the plants that @Courtney is currently growing?
Am I correct in assuming that any black viable seeds in a seedless watermelon are infrequent as it needs to be pollinated at a precise stage in order to occur?
Do you happen to have any links to a paper I cold read on this topic? I would ask you to write the non-simplified version but have a feeling that it would be rather lengthy, so links to something would be awesome. I would love to spend an evening or two trying to get my head around it.
I don’t have a link to anything documented. I delved into this question for a different plant species which is why I have some background. Tetraploid is far more likely than diploid. If it turns out to be tetraploid, apply pollen from a diploid and make your own triploid seed.
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Interesting…the seedless seed is still going strong today…not sure for how long but here’s a pix from today. The vines still look good!
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I find this topic fascinating and have been learning a lot both here and elsewhere.
While we are on the topic of fertile seeds from triploids, @Fusion_power (or anyone) could you explain to me how diploid apples produce seeds? Is it similar as the watermelon example above? Triploid apples pollinated with a diploid produce many seeds which are often viable. If I grow them out what ploidy level would I likely expect?
diploid is what we consider normal. 1 set from the pollen 1 set from the ovum. Triploid trees usually produce sterile pollen but the ovum are receptive and when pollenated apple tree will produce seeds. These resulting seeds are alloploid meaning they contain a mismatch of chromosomes not a simple doubling, tripling etc. These seeds grow with various degrees of success. But when you process thousands of triploid apples for juice, sause etc you have 10’s of thousands of chances for success.
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I have also been reading a little in here: Horticultural Reviews: Wild Apple and Fruit Trees of Central Asia - Google Books
It said “the crossing of triploid species with diploid apple varieties gave mostly triploid hybrids, but seldom tetraploid. Apomixis was a dominant factor in F1 progeny”.
Here is the latest on that seedless seed. I had to cut it as the vines are dying.
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Not bad considering it should have hold on for another few days! It was a nice dwarf sized considering I didn’t expect much of nothing😂
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