Farmer's Weekly (South Africa)
What are cucurbits?
Cucurbits belong to the Cucurbitaceae family. Often, when I mention cucurbits to friends and clients, they think I’m referring to cucumbers. But cucurbits are a very large family embracing 118 genera and 825 species.
The species important to us are:
• Cucurbita pepo, which includes gem squash and marrows, as well as Halloween pumpkins, which readily cross with the first two. A pumpkin cultivar of this species, Lady Godiva, produces the green, edible seeds often sold in health shops;
• C. maxima, which includes pumpkins and Hubbard squash;
• Butternut squash ( C. moschata);
• Watermelons ( Citrullus lanatus);
• Cucumbers ( Cucumis sativus);
• Melons ( C. melo).
This family of vegetables is one of the most important in the world, and includes the oldest vegetables to be cultivated by humans.
original wild cucurbits had a bitter taste, but this trait was bred out
The varieties used today are very different from the original wild species. For one, the latter had a bitter taste to reduce damage by insects and animals, a characteristic bred out by careful selection. Interestingly, some of the wild species still grow in the drier areas of South Africa.
Farmers often ask me if they can plant different species alongside one another, thinking this might affect the fruit produced or they won’t be able to use the seed for planting again. They need not worry; different species will not cross with one another by conventional breeding.
Sometimes, we see a photograph of a gigantic gem squash in a local newspaper and wonder how that could have happened. This is usually a cross between a gem and a Halloween pumpkin, which are simply different cultivars of the same species. Bees often travel considerable distances, and can bring pollen from a Halloween pumpkin planting that the gem squash grower is unaware of.
Another example of this is when a marrow seed pollinates a gem squash; in this case, the larger fruit in the next generation is usually oval.
C. pepo is native to the higher elevations of Mexico and Central America; C. maxima originated in Uruguay and Argentina; and C. moschata came from the subtropical areas of Mexico and South America. Those who grow cucurbits will have noticed that this species is more heat-resistant than gems, marrows and pumpkins.
Watermelons
The Cucumus genus is divided into two groups: C. sativus (cucumbers) from India, and C. melo (melons) from Africa and Asia. Citrullus lanatus (watermelon) originated in India and Africa. The watermelon is the most widely grown of all the Cucurbitaceae. The seedless variety is produced by a chemical process that doubles the chromosomes of one parent.
The ‘normal’ watermelon has 22 chromosomes. When sex cells are formed at cell division, the pollen and egg each has 11 chromosomes. At fertilisation they come together to produce 22 chromosomes again. This is called a diploid.
When a plant with doubled-up chromosomes (44), called a tetraploid, is crossed with a diploid, the seed will have 33 chromosomes. This is called a triploid. With this ‘unnatural’ cross, no seed is formed in the fruit and no pollen produced. A fertile plant has to be planted with it to produce fruit.
More on this later when we discuss watermelon production. • Bill Kerr is a vegetable specialist and a breeder of a range of vegetables. Email him at farmersweekly@ caxton.co.za. Subject line: Vegetable production.