chlorosis, symptom of plant disease in which normally green tissue is pale, yellow, or bleached. It results from failure of chlorophyll to develop because of infection by a virus; lack of an essential mineral or oxygen; injury from alkali, fertilizer, air pollution, or cold; insect, mite, or nematode feeding; gas main leaks; compaction or change in soil level; and stem or root rot. Severely chlorotic plants are stunted, and shoots may die back to the roots. Control is aimed specifically at the causal agent of the disease.