Sporulation in Alternaria cichorii is controlled by a blue and near ultraviolet reversible photoreaction

Sporulation in Alternaria cichorii Nattrass was induced by near ultraviolet irradiation (< 340 nm) and inhibited by blue light. The inhibitory action of blue light could be reversed by near ultraviolet irradiation. Induction by near ultraviolet could be annulled by subsequent exposure to blue light. Sporulation during a sequential exposure to blue–near ultraviolet light was always determined by the quality of the last irradiation applied. A series of alternating doses of blue–near ultraviolet light ending in near ultraviolet promoted sporulation whereas a series ending in blue light inhibited sporulation. This is considered strong evidence for the existence of an interconvertible pigment system absorbing at the blue and near ultraviolet regions of the spectrum which controls sporulation in A. cichorii.