The wart-like protuberances on the pumpkin fruit below have a physiological (abiotic) cause. Edema has been seen rarely, and mostly on the side of the fruit in contact with the ground. Conditions under which it occurs are air being cooler than the soil, high soil moisture, and high relative humidity. Low plant transpiration rates combined with an increase in water absorption by roots from the soil leads to increased cell turgor pressure, resulting in eruption of epidermal cells as the inner cells enlarge. Protrusion of the inner cells causes epidermal cells to die and discolor, resulting in a warty appearance.
