First report of rubbery rot of potato caused by Geotrichum candidum in the Krasnoyarsk region

The purpose of the study is to identify pathogens of rot of unknown etiology that affected potato tubers imported from the Astrakhan Region in 2022, as well as potatoes produced in the Minusinsk District of the Krasnoyarsk Region. In both cases, the cause of the rot was the causative agent of potato rubber rot, the fungus Geotrichum candidum Link, belonging to the kingdom Fungi, division Ascomycota, class Saccharomycetes, order Saccharomycetales, family Dipodascaceae, genus Geotrichum. This is the first case of identification of this phytopathogen on potatoes in the Krasnoyarsk Region. According to literature data, even planting tubers slightly affected by rubber rot lead to a 20-30 % reduction in yield and 15 % yield loss during storage. The fungus reproduces using rectangular (less often round) arthrospores measuring 5.0-12.6 × 3.0-5.5 µm, which in model experiments at a temperature of 25 ± 1 °C are formed 13-14 hours after artificial infection of the tissue tubers. Due to the fact that the symptoms caused by G. candidum on potato tubers are similar to the symptoms caused by a number of other phytopathogenic fungi, a biological method should be used to reliably diagnose the pathogen. As a diagnostic sign, we recommend using the formation of arthrospores of G. candidum on the affected tissues in situ or after 14-24 hours of incubation in a humid chamber, as well as the germination of arthrospores by mycelium with characteristic dichotomous branching of individual hyphae and rapid fragmentation of hyphae into arthrospores.