In general terms, fruit is the protective organ of the seeds. In most cases, without seed formation, there is no development of fruit and without flower, there is no seed. But in some plants, it is known that some parts of the plant get modified by the deposition of starch or the food produced by the green parts of the plant. And we also use the storage parts of plants like fruits and vegetables. So it would not be wrong to say that fertilization is not the only method to develop fruits in plants.