l Faculty of Forestry, University of Belgrade, 11.030 Belgrade, Yugoslavia

Background and objectives
During 1992, in region of Durmitor and Bjelasica, a new disease of fir needles (Abies alba Mill.) was observed, which only occurred on trees above 1700 m altitude. Recently (during 1997) in the region of Durmitor this fungus was observed also on the needles of Abies borisii regis Mattf. On Durmitor, the damage was especially noticed in silver fir stands above Lake jablan (altitude between 1750 and 2000 m). These trees occur along the upper limit of the natural range of silver fir in this region. The symptoms of the disease were observed on needles of all ages and on some trees more than 80% of needles were necrotic. Long term infection, associated with other adverse factors, caused the death of trees at some places. Examination of needles showed that necrosis was caused by a fungus belonging to the genus Tiarosporeila, which could not be assigned to a known species, but is very close to Tiarosporelia abietis which occurs on Abies species in Canada [2]. The fungus is described as a new species and the results of patogenicity tests are presented [1].

Materials and methods
Since 1992, when this fungus was recognized for the first time, the material has been collected several times in silver fir stands in the region of the National Park Durmitor and in the region of the National Park Biogradska Gora. The identification of the fungus as Tiarosporeiia sp. was made on the basis of the morphology of the pycnidia and the conidia. The effect of temperature on the growth of the fungus was tested on MEA and PDA. The following temperatures were tested: 00, 50, 100, 120, 140, 160, 200, and 250. A series of experiments was made with artificial inoculations of Abies alba and Picea abies seedlings. For infection, 4 and 5-year-old nursery plants were used. The plants were inoculated by spraying with a water suspension of conidia from the pycnidia formed on fir needles.

Results and conclusions
The fungus Tiarosporelia durmitorensis is very similar to T. abietis but forms larger conidia. It also differs morphologically and ecologically from other Tiarosporella species on conifers. Therefore, it is described as a new species. Morphologically very similar to T. durmitorensis is the fungus T. parca. However, these two fungi differ by their host plants, in that T. parca occurs on the species of the genus Picea, while T. durrnitorensis infest A. alba. On mount Durnitor firs and spruces occur together. A severe attack of T. durmitorensis was observed on fir needles only, and there were no cases of spruce needle infection.
The culture of the fungus T. durmitorensis was very slow growing. The average radial growth of the colony, at the optimum temperature of 14'C amounted to 0.5 mm daily on MEA. The growth occurred between 00 and 200C. The conidia germinated at temperatures between 00 and 200, the optimum temperature for for germination being between 120 and 140C.
Experiments with artificial inoculations (conidia suspension) of fir seedlings in controlled conditions showed that this fungus is a very aggressive parasite.Needle infections were successful on all the silver fir plants held in incubators at 100 and 160C. The percentage of infected needles on the fir seedlings was almost 100%. Conversely, all attempts to infect needle of spruce seedlings with the conidia of T. durnitorensis were unsuccessful. This is a clear indication that T. durmitorensis is adapted only to fir needles.
For the time being, it can be stated that T. durmitorensis is a very aggressive pathogen colonizing fir needles of all ages. Together with other fungi, it leads to tree death, but only in the alpine region at the border of the natural range of silver fir and a places where the snow stays throughout the winter.

1. Karad2id D, 1994. Plant Protection Today and Tomorrow, Beograd, pp. 137-144. 2. Whitney HS, Reid J, Pirozynski KA, 1975. Can. J. Bot. 53, pp.3051-3063.