Apple

Apples appear in the background in various media in the How to Train Your Dragon Franchise.

Physical Description
Apples are the fruit of the Apple tree in the Genus Malus. This genus can include the larger sweet apples that are widely cultivated, or other species with smaller more sour fruits referred to as "crabapples". Apple trees are mid-size deciduous trees that actually belong in the rose Family (Rosaceae).

Function
The main function in both reality and the Franchise for the apple is food. It can be eaten raw or cooked and preserved in a variety of ways. Even the wood of the apple tree emits a pleasant smell when burned and is used to impart different flavors to smoked foods. In "How to Start a Dragon Academy", a dragon is seen stealing a bag of apples, indicating that dragons probably like to eat apples, too.

The apple also figures into several cultures' mythologies, including Norse. The Goddess Idunn is said to give out apples daily to the Gods that keep them youthful.

Dragons: Riders of Berk
In the episode, "How to Start a Dragon Academy", the dragons are running amok in the village of Berk, breaking things and stealing food. A Monstrous Nightmare steals a bag of apples from a village man, yanking it from her hands.

Dragons: Defenders of Berk
In "Worst in Show", the Dragon Riders train Terrible Terrors. Fishlegs trains one named Iggy. He is able to show him a picture, which the dragon then retrieves. One of the pictures is of an apple.

In "Zippleback Down", Ruffnut is knocked unconscious by an apple thrown by a Terrible Terror.

Dragons: Race to the Edge, Season 1
Fishlegs, as an alter ego named Thor Bonecrusher, saves a baby from an out of control cart of apples.

Dragons: Race to the Edge, Season 4
In "Midnight Scrum" Hiccup gets chased by various bounty hunters on an Unnamed Island. Astrid and Toothless hear is need for aid. Toothless drops the bucket of apples he had collected and rushes to his rider's side.

School of Dragons
Apples appear in the player quest "Prepare for the Big One!", in which the player must collect apples in the Wilderness area of the School of Dragons Island.