The genus Cucumis has a bunch of useful species. The most familiar one is the common cucumber (C. sativus). That species name indicates that the plant was originally considered a medicinal herb. Cucumber seed can be ground up as a treatment for tapeworms and the leaves were used as a diuretic (though do your own research before attempting these uses). The other most familiar species is C. melo, bred into the rockmelon/cantaloupe/muskmelon but also used as a vegetable in Asia in the form of varieties like the Armenian cucumber, and some African forms are grown for edible seeds. Minor species in the genus include the West Indian gherkin (C. anguria) and the focus of this post, the kiwano from southern Africa (C. metuliferus).
I was never much of a fan of growing cucumbers since they need to be harvested religiously and yield little more than crunchy water for all that effort. I did dabble with storage cucumbers, which could be pickled at my own pace, but again all that work would yield little more than pickled water. My husband is a big fan of rockmelon, and I did a few variety trials looking for any genetics that grew well here but nothing stood out. Watermelon was a much easier way to fill this niche as a sweet summer fruiting cucurbit. So for the last few years I put the genus aside, despite its obvious potential.
This all changed when I learnt about egusi watermelons that produce a large amount of edible oil seeds instead of sweet flesh. This is a much better use for the genus Citrullus. The possibility of growing rockmelons to fill the fruit niche came up again, but the issue of weak growth continued to put me off. So I decided to take a chance on whipping up a mutant melon monster to serve this purpose.
The kiwano melon is the best starting point for this scheme. It grows easily in a similar climate in South Africa and stood out during a small trial many years ago. I bought four different strains of seed to give myself the best broad genetic foundation (all unnamed orange forms- there are white and red skinned ones in circulation overseas as well). They were direct sowed into an awkward bed on the edge of my summer vegetable garden. They got off to a slow start due to the dry weather, but once the rain hit, they took off. I pruned back the vines threatening to swamp their neighbours for a while, but eventually was overwhelmed. This species is phenomenally vigorous compared to its relatives, just what I need to give rockmelons the necessary push toward greater vigour.
As soon as I saw the first kiwano fruit ripening I put on my leather gloves and long sleeve shirt to cut out the plants. I want to avoid rotten fruit self-sowing and causing problems. The vines are incredibly prickly- somehow teleporting their spines through my gloves to lodge in my thumb. The fruit are also covered in spikes like little landmines waiting for unwary feet. Each plant produced about 10 kg of fruit in the end. They took me a few tries to warm up to, but the scooped out seedy green pulp is a refreshing snack on a warm autumn day. The best ones taste like watered down passionfruit with a hint of lime. The four strains showed some moderate variations in fruit shape and plant vigour, so I will keep the four maternal strains separate for future breeding work (though they undoubtedly cross pollinated). Seed needed to be lightly rotted in a colander for a few days, with regular rinsing, until the gel capsules could be squished off by hand so the seed could be dried for storage.
Research indicates that C. melo and metuliferus are not generally cross compatible, though there is a single record of an Indian vegetable form of melo succeeding. Luckily C. metuliferus and anguria cross fairly readily, so I plan to recreate this cross by hand next summer. Often a freshly hybridised strain has lower hybridisation barriers, so it will be worth trying a cross of (anguria x metuliferus) with rockmelon strains of melo the following year.
There is one other way for rockmelons to steal some kiwano vigour. Cucurbits can be readily grafted at the seedling stage, so the first phase will involve variety trials of rockmelon grafted onto kiwano rootstocks. There are two main techniques- either a slicing side graft or drilling into the rootstock to do a plug graft. I’ll experiment with both approaches to see what works best for me. Once I master the technique with bulk rockmelon seed I saved from a store bought fruit I will buy a wider variety of rockmelon genetics to do a grafted variety trial. If I can select varieties that grow through spring to ripen around Xmas time it will fill a particularly empty gap in the fruiting calendar. Muskmelons generally like cooler temperatures and lower humidity than watermelon, so there should be strains that will grow through this dry season provided their rootstocks are vigorous enough.
I don’t want to continue grafting forever, so there is one final technique I hope to try. When different plants are grafted it is possible for heritable traits to be transferred from the rootstock to the scion. The chance of this happening can be increased by a technique called mentor grafting. The trick is to remove the leaves to the scion, while leaving plenty on the rootstock. This encourages sap flow from the rootstock, which increases the chance of it carrying organelles, proteins and nucleic acid sequences (packaged in little vesicles called exosomes) that are absorbed by the recipient plant. Only a small percentage of grafted plants experience any noticeable transformation, and which traits are transferred is unpredictable. I suspect the symbiotic microbes that live inside all plants are also probably transferred under such conditions. Mentor grafting has also been known to lower hybridisation barriers between species. Recently hybridised scions are also meant to be more receptive to absorbing genetic material from the rootstock. Perhaps the reverse is also true and I plan to try using metuliferus x anguria as rootstocks as well.
All of this is a long shot project, aimed at a crop that will produce sweet and smelly water if all goes well. Usually, I wouldn’t bother in such cases, but my husband has been so critical in making my lunatic dreams come true. The least I can do is create a new species in return.
PS- In other news, recording of the audiobook of Taming the Apocalypse is complete, so the final stage in production should be done in coming weeks. Paid subscribers to my substack will get access, both to the ebook in blog post format, and the audiobook as a series of podcasts. Distribution through other channels will follow shortly .
I'll be really interested in the crosses you end up with from this. Hopefully you get something sufficiently vigorous and tasty that it just seemingly comes back on its own to treat you and hubby each season.
Hope the donkeys are still settling in well also. Loved the recent podcast about tuberous peas as well.
Even if it's just pleasantly smelly sweet water, I have a soft spot for delicious fruit that requires 0 effort. I'm forever grateful to the cockatoos and bats that shit out passionfruit and guava seeds all over the place so I only need to walk down the road to the creek to pick passionfruit in February and again now until June + guava from March all the way through to the end of the crop in early May.
Guavas picked just as they start showing yellow and ripened inside on the bench have extremely low rates of fruit fly larvae in my experience and are just as sweet as tree ripened. Now we're getting cooler nights most of the ripe yellow fruit that hangs on the later fruiting trees have no larvae so I can be even lazier picking them + the bats and birds have moved on so the vertebrate pressure has subsided. I don't know why people bother netting them in SEQ.
The Surinam cherries have been slow to flush properly again since Christmas, just sporadic fruiting here and there whereas last year there was a solid 2 crops after new years. I found one tree, which from it's placement is obviously bat or bird planted, that has sweet, red, low resin fruit even when not quite fully coloured up. It's near the local shops so I don't always get to it at the perfect time but even slightly immature fruit are great. The winter crop is a fruit fly free, aromatic delight. Better even than a fully ripened black variety. I've started a few seedlings from it.
I have some slender celery (cyclospermum leptophyllum) seed for you and I could also send some seed from the sweet Surinam if you're interested.