Studies on the dissemination of peach anthracnose II.

Abstract

The twig of peach infected by anthracnose fungus, Gloeosporium laeticolor, usually dies till March, and conidia may be formed on these killed twigs in April. On the twig, conidiophores develop sparsely and not mucilaginous, giving quite different appearance from acervuli on the fruits.Primary infection occurs on the trichomes of young peach fruit. Spore, stuck on the trichome, germinates within about 12 hours, and forms appressorium at the apex of germ tube and penetrates the cell wall. About 2 days later, acervuli develop over the surface of the trichome. Affected trichomes turn brown in colour. They are easily detatched and blown off by the wind. Accordingly these infected trichomes play an important role as a source of initial secondary infection. In addition, the fungus may invade into the young fruit tissue through the affected trichomes.The anthrachose fungus can also invade both young peach leaf and nectarine fruit, without forming appressorium at the entry point.On the young fruit, acervuli are formed 48 hours after inoculation. Acervuli on the leaf are faded brown in colour and pulverlent, while the acervuli on the young fruit are light brown or light salmon in colour and mucilaginous.Peach fruits may be infected at any time during their growth period from May to August, if the weathers are favorable to the dissemination of the pathogene. The conidia are hardly blown off by the wind unaccompanied with rain. But if it rains, conidia will be suspended in the rain droplets, which will be splashed by the wind. This infections of fruits on a peach tree spread conically, in a form of “Infection cone” (DUNEGAN, 1932). The conidia fallen on the soil surface may remain alive for about 7 days in summer.