On the promotion of senescence in Brassica oleracea var. capitata by Alternaria brassicicola and by Botrytis cinerea

Abstract

Alternaria brassicicola and Botrytis cinerea stimulated ethylene production in closed culture with floating leaf discs from cabbage (Brassica oleracea var. capitata). Production with A. brassicicola had an observed maximum at 18 °C and was speeded by preculturing the fungus on media containing cabbage components, but which contained little or no methionine.In the absence of cabbage tissue, both organisms demonstrated a latent capacity to generate ethylene from closed shake cultures of Czapek's medium containing L-methionine. With A. brassicicola in a modified Czapek's medium (minus ferrous sulfate) containing 10−3 ML-methionine, there was a stimulation of ethylene production at 18 °C by the addition of Fe2+, Fe3+, Cu2+, ca. 8% carbon dioxide, or the potassium salt of gibberellic acid (GA3). With B. cinerea, 4% carbon dioxide was stimulatory, 29% carbon dioxide was inhibitory, whereas less than 4% oxygen arrested the production of ethylene completely for 48 h.Results suggest that the nature of parasitism of A. brassicicola and B. cinerea on cabbage is characterized by a latent capability to cause the production of, and to produce, the plant-senescing hormone ethylene.