Significance of wounds on citrus fruit peel in the infection process of Penicillium digitatum Saccardo
1987
Kawai, M. | Homma, Y. | Arimoto, Y. (Riken, Hirosawa, Wako-shi, Saltama (Japan))
Wounds on citrus fruit peel caused by Penicillium digitatum are the usual sites of invasion by this fungus. The role of wounds in the infection process was studied in detail. This fungus hardly caused infection through the wounds of fruit peel which was cut by a blade and immediately washed with distilled water ("washed wounds"). This suggested that the infection was affected by the cell sap exuding from wounds of fruit peel. The extract obtained from the cell sap of fruit peel was effective in inducing hyphal penetration into the plant cells. Also, the conditions of both the citrate concentrations of 2.5 x 10 to the negative third power -5 x 10 to the negative second power M and the ranges of pH 3.1-3.8 induced the infection through the "washed wounds" and hyphal penetration into the plant cells as similar as the extract of fruit peel. However, no induction occurred in the other citrate concentrations and/or pH ranges. Fruits at harvest time are readily invaded by this fungus, whereas unripe fruits before that time are hardly invaded. The seasonal changes in the wound infection by P. digitatum were intimately related to the seasonal changes in both the citrate and pH conditions of fruit peel. Furthermore, the wound infection through these unripe fruits was promoted, when under the optimum conditions in both citrate and pH, conidia of P. digitatum were inoculated. Thus, the present results would indicate that the wounds of fruit peel contributed toward supplying both the optimum citrate concentrations and pH conditions controlling wound infection by P. digitatum.
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