What process wilts a plant as a result?

There are many possible reasons. Here are a few:

1. not enough sunlight, or too much sunlight (relative to each plant)

2. root rot: this happens when the plant is getting too much water. the roots of the plant are sitting in stagnant water and begin to rot, which kills the plant. make sure to give the plant enough water, but don't soak the soil.

3. nutrient deficient soil: some soils simply lack the nutrients the plant needs. you can add compost, seaweed liquid fertilizer (which is totally organic), or even urine ( i know it sounds gross but it contains alot of nitrogen)