Mycobiota of Castanea sativa Mill. in Azerbaijan - WSL

406 Dilzara N. Aghayeva
A drying process has been observed in chestnuts in forests, plantations and private plots in
the Great Caucasus. The intensity of dieback is 45 to 50%. The purpose of this study was to
investigate the mycobiota involved in chestnut dieback.
2 Materials and methods
The fungi were isolated from drying chestnut trees in mixed forests or chestnut plantations that
were 30 years old or older. Leaves, dead and living branches and xylem from trees attacked by
bark beetles were observed under the microscope (MBR-3). Specimens in which it was suspected
that species of Ceratocystis were growing, but not yet sporulating, were placed in a damp chamber.
Fungal isolations were made by transferring spore masses to MEA (20g malt extract, 20g agar per
L water). Identification was made according to POTLAYCHUK and SHEKUNOVA (1985). Mor -
phological traits in culture, optimum pH and temperature optimum were determined according to
BILAY and ELLANSKAYA (1982). The growth of the fungus was studied in liquid glucose-mineral
medium with the pH ranging from 4.5 to 7.0 at 28 °C. The growth was measured by weighing the
dry biomass. Optimum growth temperature was defined on MEA by measuring the diameter of
the colonized area (in mm). The effect of humidity on the germination of spores was studied
according to KHOKHRYAKOV (1976) in the exsiccator with humidities of 50, 60, 70, 80, 90 and
100%. Spores on the dry glass slide were placed in the exsiccator at the optimal temperature of
28 °C. All experiments were performed three times. The carbohydrate and nitrogen requirements
of the fungus were studied on Czapek’s agar (20g sucrose, 2g NaNO 3, 1g KH 2PO 4, 0.5g MgSO 4
7H 2O, 0.5g KCl , 0.01 g FeSO 4 per L water) with a minor modification (BILAY 1978): Sucrose was
replaced by 20g maltose, glucose, cellobiose or cellulose each. 0.4% of NaNO 3, NH 4NO 3,
(NH 4) 3PO 4, urea or asparagin were used as nitrogen sources. Media without any carbohydrate
and nitrogen sources served as controls. The growing temperature was 28 °C.
3 Results
The first symptoms of chestnut drying appeared in June. Leaves became red, gradually
turned yellow, dried out and fell off. Drying began from the top of trees. At first thin, one to
two year old summer branches died back, then the thicker branches. The process of drying
spread down along the crown gradually. Dark brown lines and dark or brownish wood
elements were noted under the bark of the drying trees. Chestnut drying is chronic in nature
and complete drying out of trees can be observed within 4 to 10 years. This drying has been
noted since 1981 in Great Caucasus. The following fungal species were recorded on the
affected chestnut wood, twigs and leaves: Ceratocystis castaneae (Vanin et Solov.) C.
Moreau, Sphaeropsis castaneae Togn., Diplodia castaneae Sacc., Phoma endogena Speg.,
Cylindrosporium castaneae (Lev.) Krenner., Coryneum kunzei Cda., Cladosporium sp., and
Mycosphaerella sp. Cryphonectria parasitca was noted only once in 1942 in Azerbaijan. Since
then it has no longer been found (unpublished data).
Ceratocystis castaneae was found under the bark of drying chestnuts in the Gabala forest
for the first time in 1981 and again in 1994 (GUSEYNOV and AGHAYEVA 1997). Since 1994 it
has been observed in other forests too (mainly in Great Caucasus). Perithecia develope
abundantly on xylem. In culture, colonies are fast growing, covering a petri dish in 15 days at
25 to 30 °C. In the beginning the colonies are white, later becoming white to grey. Both
Sporothrix (Hektoen et Perkins) and Graphium (Cda.) types anamorphs have been recorded.
The conidiophores of Sporothrix anamorphs are clearly branched, hyaline, septate, 33.6–47.6
(42.9) x 2.5–2.8 (2.4) µm. The conidiogenous cells arise terminally on conidiophores as
sympodial denticles. Conidia are holoblastic, hyaline, thin-walled, unicellular, oblong to
ellipsoidal, clavate, 2.8–5.6 x 1.1–1.5 µm. They are formed singly, later becoming aggregated
in a slimy mass. The coremia of the Graphium type are brown, black, pale brown or subhya-