A cracked tongue may indicate an oral yeast infection, or oral thrush. Oral thrush is caused by the accumulation of the candida fungus in the lining of your mouth. In addition to cracks, symptoms of oral thrush include pain, loss of taste and lesions on the tongue and other areas in the mouth. A weak immune system, diabetes, cancer and vaginal yeast infections are all causes of oral thrush, according to MayoClinic.com.