Seasional Variation in Crown Rot of GF677 and KID I Peach Rootstocks by «Phytophthora cactorum», «P. citrophthora» and «P. syringae»

Abstract

Seasonal variation in extent of colonization of GF677 and KID I peach rootstocks by P. cactorum, P.
citrophthora, and P. syringae was examined on excised twigs in vitro, and by stem inoculations in the experimental
field of the Pomology Institute, Naoussa, Greece. Shoot segments of the previous growing season were cut and inoculated
in the laboratory in the last ten days of August, 1998, and at monthly intervals thereafter until July 2000. At
the same time, rootstock stems were also inoculated directly with mycelium of the pathogens every month. Disease
severity was assessed 14 days after inoculation. Both P. cactorum and P. citrophthora showed two peaks in the extent
of colonization, one in April-June, and one in September and October. In contrast, no colonization of plants occurred
in July-August or in January-February. P. syringae also had two peaks in its extent of colonization, one in November-
December and one in March. This fungus was inactive during May-October and January. The maximum and minimum
extent of pathogen colonization on plants coincided with maximum and minimum growing temperatures of the
fungi. The identification of seasonal variations in the susceptibility of peach trees to Phytophthora may facilitate the
timing of disease control measures which should coincide with periods when fungal growth is most rapid.