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Accessible Science: May 9

Each day we are presented with a plethora of options in the Caf. Being able to pick and choose what to eat may create a sense of independence or empowerment. However, we would be silly to think we are the only ones chosing our food. Thousands of decisions made over hundreds of years by people across the world are behind every food item in the caf. Be it rice, beans, carrots or fruit, they all have been carefully cultivated for us.

Apples are perhaps one of the most recognizable fruits worldwide. While the ancestors of apples originated in the mountains of Kazakhstan, they are now found thriving in faraway places such as New Zealand and Minnesota. The apple’s ability to thrive in many different environments is a testament to their great amount of genetic variability; there are thousands of varieties in the world. Genetic variability is made possible by the crossing over and mixing of genes through sexual reproduction. For plants, this occurs when the pollen of a male flower fertilizes the ovule of the female flower.

We depend on new combinations of genes to create new and desirable types of apples. However, once a specific cultivar is identified, orchardists can only ensure a consistent fruit by using a technique called grafting.

Grafting is a form of vegetative reproduction in which, unlike sexual reproduction, no mixing of genes occurs. This means that each generation maintains the desired traits of the previous generation. Orchardists graft apple trees by clipping buds from the mother apple tree and implanting them into a young stock tree. With special care the tissues of the two trees fuse together. Thus, when you see a fully grown apple tree you can know that the fruiting branches are actually from a tree different than that of the trunk and roots. This is how orchardists ensure the same crunch and sweetness for each generation of apples.

Oranges are also grown on grafted trees, although they are not optimized to grow in as many places as the apple. The oranges, which we enjoy year round, are usually from California or Florida and are the result of one genetic mutation that was discovered in the early 1800s. This mutation caused the development of a second ovary embedded within the original orange. The secondary ovary grows and protrudes from the larger one giving the appearance of a belly button.

This mutated fruit was selected for further cultivation because it produced fewer seeds and is sweeter than other varieties. It also has a thicker rind making is ideal for transport. The rind, although tough and bitter, is what gives oranges their irresistible smell. The aromatic oils contained in the rind burst when peeled and are actually quite flammable.

Perhaps the most coveted fruit in Stav Hall is the banana, another fruit produced via asexual reproduction. This exotic fruit is only available at breakfast and has the potential to disappear from shelves forever as a result of their genetic uniformity. Having the same genes provides them with the same defense, or lack of defense, against pests and disease. While the pests are evolving and getting stronger, the banana plants stay the same, requiring heavier use of pesticides. The concern is that a fungal disease called the Black Sigatoka could damage so many plants that cultivation and production will become economically unviable.

The large majority of bananas that we eat today are the Cavendish banana. It’s predecessor, the Gros Michel, was wiped out by Panama disease in the 1950s. Should the Black Sigatoka knock out the Cavendish, we may not see bananas for several years until producers find a viable replacement.

Many of us consider fruits a simple food. What we see on the tree ends up on our plates. However it’s important to appreciate the deliberate and long history of cultivation that has made our apples, oranges and bananas available to us on a daily basis.

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