LEAF SPOTS at first not numerous, single, red brown, 1-2 mm diam, usually vein-limited, later numerous, brown, confluent, and finally frequently transform into large, brown, necrotic areas. On the under leaf side, directly below the spots, small, 172-320 µm diam, elevations form, under which acervuli origin. Severely affected leaves, prematurely fall off.

ACERVULI (a) subepidermal, 270-290 µm diam, 80-100 µm high, composed of a basal wall and of conidiogenous cells lining the upper surface of the wall.

Wall (w) composed of thin-walled, tightly adherent cells.

Conidiogenous cells (cc) hyaline, conical, 5-12 µm high and 2-3.5 µm wide.

CONIDIA (c) hyaline, cylindrical to crescent roll-shaped, narrowing towards their ends, with a sharpened tip and a blunt base, euseptate or sometimes septate.

PLANT HOST AND DISTRIBUTION. Phloeosporella padi occurs on Cerasus avium (L.) Moench, C. fructicosa Pall., C. vulgaris Mill., Prunus insititia L., P. spinosa L., and other Prunus species (Arx 1987; Kochman 1973).

Phloeosporella padi has been reported from many regions of Europe, as well as from USA and Canada (Kochman 1973).

NOTES. The teleomorph of P. padi is Blumeriella jaapii (Rehm) v. Arx. Phloeosporella padi has been originally described as Cylindrosporium padi (Lib.) Karst. However, Arx (1961) found that the acervuli of P. padi develop subepidermally, whereas those of species of Cylindrosporium origin subcuticularlly or intraepidermally. Consequently, he transferred this fungus to the genus Phloeosporella.

Phloeosporella padi is the causal agent of cherry leaf spot or shot hole yellow leaf (Holliday 1989).

During vegetation, P. padi spreads by conidia transported by wind and rain (Kochman 1973). The conidia germinate in water and penetrate into leaves through stomata. At a temperature of 20-25oC, the conidia germinate after ca. three hours.

The fungus overwinters in fallen leaves. The sources of primarily infections are ascospores of B. jaapii formed in dark, leathery or fleshy apothecia (Smith et al. 1988). They are forcibly discharged during any rainy period from that time until 6 or 7 weeks after petal fall. The fungus penetrates through stomata.

REFERENCES

Arx J. A. 1961. Uber Cylindrosporium padi. Phytopathol. Z. 42, 162-166.

Arx J. A. 1987. Plant pathogenic fungi. Beih. Nova Hedwigia 87, 1-288.

Holliday P. 1989. A dictionary of plant pathology. Cambridge University Press. Cambridge, New York, New Rochelle, Melbourne, Sydney.

Kochman J. 1973. Fitopatologia. PWRiL. Warszawa.

Smith I. M., Dunez J., Lelliott R. A., Phillips D. H., Archer S. A. 1988. European handbook of plant diseases. Blackwell Scientific Publications.