Ecology of larch black leaf rust in Russian Far East

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Larch black leaf rust was known to occur on Larix species in northeast China and adjacent areas. The rust was found on L.gmelini in the Primorski District, Russia in 1994. The disease incidence was sever and indicated that the causal fungus has potential to devastate larch stands, which are the major component of the Taiga vegetation, whenever environmental conditions favor the fungus to spread and infect. Nevertheless, virtually nothing is known as to its life cycle, host specificity and primary inoculum in nature, all of which are indispensable in order to develop the ecology-based effective control measures of the disease. In this context, field observations were carried out in Vladivostok, Ussuriski and Sikhote-Alin Nature Reserves, and Mt. Livadiskaya in the Primorski District and Yakutsk in 1995. The rust was only found on L.gmelini in the Sikhote-Alin Nature Reserve where the rust seemed to persist steadily. As to life cycle of the causal fungus, its uredinial stage was found for the first time in nature, indicating that the fungus multiplies and widely disperses by the vegetatively reproducing urediniospores. Inoculation experiments proved this presumption ; the urediniospores formed on L.gmelini was successfully infected L.gmelini and L.kaempferi reproducing uredinia first and then telia on both species. Further inoculation experiments are now being made to find out entire life cycle of the larch black leaf rust fungus.