Phytosanitary monitoring of lavender diseases.
In the period 2008-2009, fungi of the genera Phomopsis, Phoma, Septoria, Phytophthora, Alternaria, Fusarium and Botrytis were isolated from diseased parts of lavender plants (Lavandula officinalis): stems, base of branches and leaves. Based on morphological characteristics, the following species were identified: Phoma lavandulae, Septoria lavandulae, Phomopsis lavandulae (Gabotto) Cif.&Vegni and Phytophthora nicotianae Breda de Haan, syn. Phytophthora parasitica (Dastur, 1913). The last two are new pathogens for lavender in Bulgaria. Phomopsis lavandulae attacks stems and gives grayish discoloration to the leaves. The pathogen forms roundish to pyriform picnidia, sized 87.5-105 µm, in the stem tissues. Conidia are two-celled, ellipsoid, slightly constricted/narrowed in the middle, with pointed ends, sized 8.75-17.5×3.5-4.66 µm. The disease is more harmful in the cases of co-infection with Phoma lavandulae and Septoria lavandulae. Lavender plants infected with Phytophthora show suppressed growth. Grayish water-soaked spots are found at the stem base and cause stem wilt and death. Leaves turn yellow-grey in color and drop off. Phytophthora is isolated from the infected stem base. Fungi sporangia vary in shape from spherical to ellipsoid, with papillae, sized 24.5×24.5 µm. Oogonia are spherical, with smooth walls, sized 25.5×24.5 µm. Antheridia are amphigynous, spherical to oval, sized 10-12×9-10 µm. Oospores are spherical, aplerotic, sized 24.5×24.5 µm. Chlamidospores are terminal or intercalary, sized 13.6×13.6 µm. Fungi from the genera Fusarium and Botrytis are also isolated from infected roots. Fungicides for the control of Phomopsis lavandulae are tested "in vitro".