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To start off, humans are interacting greatly with watermelons. Not only do we plant them, and selectively breed them, but we eat them! After the flower produces the fruit, we open it up and eat the sweet tasting flesh. You can learn all about how we use them for food under food/facts.


There are many organisms that are involved in a mutualistic relationship with the Citrullus lanatus. Mutualistic relationships are very positive, as other organisms benefit in some way. Organisms considered mutualists with the watermelon are also known as pollinators. There are a number of insects involved in pollinating the watermelon, but the honeybee is the most common.
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As talked about on the reproduction page, the honey bee plays a large part in pollinating the Citrullus lanatus, as it is their primary pollinator. Like all bees, honeybees have basket-like structures on their hind legs in order to store pollen they collect from male flowers and use it as nutrition for them. Pollen that remains on the bee outside the baskets falls onto the female flowers when they land on them, benefitting the plant by allowing it to reproduce.

Unfortunately, the watermelon serves as a host to a number of parasites. A parasitic relationship involves one organism while the other organism (in this case the watermelon) is harmed. Both fungi and bacteria are very common organisms that create symbioses with plants. When they are parasitic, they are commonly known as a pathogens. A popular fungus that causes disease to the Citrullus lanatus is the Didymella bryoniae, also known as the gummy stem blight. In addition, a common bacterial pathogen involves the disease, bacterial fruit blotch.  

Gummy stem blight, photo used with permission, UGA - McGregor Lab ( Stem Blight
This organism does well in warm, wet weather, which happens to be the exact same weather watermelons do well in. By living within the watermelon, the gummy stem blight benefits by stealing nutrients and having a safe place to live. By creating lesions on it, the watermelon suffers with negative effects in growth and reproduction. The Didymella bryoniae reproduces on crop residue. Physical symptoms of this pathogen includes indefinite-shaped lesion on the leaf, stem, or vine, lesions being chocolate brown, water-soaked stems, and the plant tissue appearing woody.

Bacterial fruit blotch
The organism that creates this watermelon disease is the Acidovorax avenae. This disease can cause the watermelon to completely stop growing, or slow down its growth, depending on the stage in the watermelon life it begins to infect. The bacteria benefits from the nutrients. It can be seen on the seedling transplants and/or the mature leaves and fruit. If the vines are infected, they do not drop their leaves negatively effecting growth and photosynthesis resources. This bacterium is identified as being small, dark, and angled.

The Citrullus lanatus is a victim of a number of different predators. A predator is an organism that harms another organism while benefiting itself. In many cases, the predator kills the other organism. Some predators of the watermelon include aphids, flea beetles, red spider mites, root-knot nematodes, whiteflies, and Epilachna beetles.
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Aphids…one of plants most common predators. Aphids are small herbivorous animals that feed via a structure called a stylet on the sugars, directly from an individual sieve tube member within the phloem cells, which is discussed on the nutrition page. The cotton aphid (Aphis gossypii) is the common aphid interacting with the watermelon. They are normally found on the lower leaf surface. This predatory relationship benefits the aphids while it provides them with direct nutrients. They harm the watermelon directly by stunting shoots and leaves, and transmitting virus diseases while they feed from one plant to another. Indirectly, the aphids harm them by leading on the growth of sooty mould from creating honeydew, which attracts fruit flies, another harm to the fruit.

Flea Beetles
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The flea beetles (Podagrica spp.) are tiny 1.5-3 mm long beetles that feed on the roots or the leaves of the watermelon. They have adapted well-developed hind legs in order to quickly jump if disturbed. As larvae, the flea beetles feed on the roots of the watermelon. As adults these beetles chew and feed on the leaves, creating holes; or they feed directly from the fruit. Often times, young watermelon plants can’t handle the predation, and it leads them to death. However, adult watermelon plants can normally handle the stress, and live through it if it’s not an excessive amount.

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Red spider mites (Tetranychus spp.) are tiny as well, being 0.6mm long and harm the leaves of the watermelons. These predators are most harmful in very dry and hot conditions. They cause young watermelon plants to die, and the adult watermelon plant to have stunted growth and a reduced fruit.
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Root-knot nematodes
Root-knot nematodes (Meloidogyne spp.) are a problem in multiple crops. They are animals that wilt the plants, distorting the roots. The distorting of the roots causes them to rot, and eventually kill the plant entirely.
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Whiteflies (Bemisia tabaci) are major transfers of disease. Much like aphids, they carry diseases from one plant to another by sucking plant sap and creating honeydew, and eventually the growth of moulds. This affects the growth of plants as well, leading to damage. Whiteflies attack many other cucurbits as well, such as the cucumber.
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Epilachna Beetles
Epilachna beetles (Epilachna chrysomelina) are 6-8mm long. Both their larvae and adult forms feed on the leaves of plants, including the watermelon. This causes the leaves to shrivel and dry up, and/or kill the plant entirely, especially young plants. These animals are also known as the African melon ladybird.


Now that you are aware of who is involved with the Citrullus lanatus, click here to learn some very interesting facts!