1979 Volume 45 Issue 1 Pages 9-16
Citrus melanose and citrus stem-end rot are caused by the same pathogenic fungus, Diaporthe citri (Faw.) Wolf. Melanose occurs on leaves, twigs and fruits, while stem-end rot does damage the fruit during storage. As a part of experiments on the mechanisms by which these diseases develop, the following results were obtained.
Conidial germination was stimulated in 0.1, 1, and 10% aqueous solutions of sucrose, glucose and fructose, the main sugars of citrus.
Germ tube elongation was greatest in a 5% solution of fructose among various concentrations of these three sugars.
Among various pH values tested, 2.2 and 8.13 inhibited conidial germination. At any pH value, conidial germination was stimulated by addition of sugars with the order of fructose, glucose and sucrose.
Of the aqueous solutions containing sugars or organic acids and adjusted pH values to those equivalent to the fruit sap in September, October, November and December, only the solution corresponding to September arrested conidial germination and germ tube elongation.
Oil gland juices obtained from the exocarp of mature fruit were tested for their effect on conidial germination and on germ tube elongation at concentrations of 25, 50, 75, 80, 90 and 100%. The 90 and 100% of oil grand juice completely inhibited conidial germination but no visible effects were found at 25 and 50%.
Inhibition of conidial germination and germ tube elongation by aceton and n-butanol extracts from pericarp suggest the presence of inhibitory substances in pericarp.
