Hetrosporium

Many species of the genus Heterosporium Klotzsch. can lead a saprophitic lifesyle, but more often they parasitize on the wild and cultivated plants from different botanic families. They affect plants of the genera Allium, Avena, Hordeum, Secale, Beta, Sorghum, Brassica, Zea, Robinia, Dianthus, Lychnis, Saponaria, Freesia, Hemerocallis, Sambucus, Galtonia, Narcissus, Gladiolus, Iris. The fungus Heterosporium gracile Sacc.1 is a causal agent of leaf blotch or leaf spot of different species and cultivars Iris L. both in Europe and America. The characteristic feature of the pathogen is its infecting the leaves of the plant. On their surface there are formed elliptic, light-fulvous, with brown edge and a lighter middle part, drying spots (fig. 1, 2, 3, 4). The area of these spots is constantly growing which causes a considerable damage ща the plant and even its death. In the middle part of the spots there can be formed brown clusters that consist of conidiophores being formed on the hyphae of the submersed mycelium, also of stroma and unripe perithecium (fig. 5, 6, 7, 8, 9, 10). Conidiophores are first straight, than variously flexious, simple or branchy, septate or not, often inflated at the bottom (fig. 6), dark-brown, olive, 20-200 x 6-16 mkm (fig. 11, 12, 13, 14, 15). Conidia are being formed on the conidiophores (fig. 16, 17). They are often solitary (fig. 18, 19, 20, 21), sometimes are formed in the short chains, cylindrical and prolonged, acanthaceous and verrucous, colored from soft to dark brown, 1-5 (mostly 2-3) septate, 20-60 х15-25 mkm, often slightly constricted at the septa (fig. 22, 23, 24, 25, 26, 27, 28, 29). The fungus H. gracile grows well in culture on PDA forming up abundant aerial mycelium (fig. 30). The hyphae of the submersed mycelium are colored from light to dark brown, flexious and septate with more thinner or thicker walls 3-14 mkm in diameter. Stroma is black, is formed out of dense hyphae interlacement. Later typical conidiophores are being formed that can be 500 mkm long, within them there are often generated endogeneous hyphae, and on the surface – conidia (fig. 31). Conidia are very fragile, even when slightly touched they can burst with its content flowing out (fig. 32). 1 McKemy, J.M.; Morgan-Jones, G. 1990. Studies in the genus Cladosporium sensu lato. II. Concerning Heterosporium gracile, the causal organism of leaf spot disease of Iris species. Mycotaxon 39:425-440.