Calcium chloride as a major component contributing to aphid resistance ofNicotiana benthamiana.

Substances with antiaphid activity were extracted from the leaf surface of aphid-resistantN. benthamiana and purified. Sugar esters and diacyl glycerols were isolated from the chloroform extract, but only diacyl glycerols showed significant activity. However, the major activity was found in the water extract rather than in the chloroform extract. From the water extract calcium chloride was isolated as the most abundant active substance. Only calcium chloride showed significant activity among several calcium salts and chlorides of several metals that are abundant in plants. Calcium contents per unit area of leaf surface ofN. benthamiana and aphid-resistantN. gossei were almost equal to each other and 10-100 times higher than that of aphid-susceptibleN. tabacum.