Concept:Gummosis is a plant disease that makes sap or gum ooze out of the bark of affected trees.Explanation:The disease mainly affects fruit trees such as citrus and stone fruits.It is caused by certain fungal pathogens that infect wounds or weak spots on the bark.The infection leads to the formation of sticky, amber-colored gum deposits on the trunk and branches.Because the primary causal agents are fungi, gummosis is classified as a fungal disease.Answer:The correct option is A. fungus.