First report of Phloeospora leaf spot on mulberry caused by Phloeospora maculans (=Cylindrosporium maculans) in the eastern Mediterranean region of Turkey

Mulberry (Morus spp.) is an increasingly important crop in the Hatay province of Turkey, mainly as a food source for silkworm. In 2002, a severe outbreak of a foliar disease was noted in almost all significant mulberry orchards. Initially, symptoms consisted of small (less than 1 mm wide) dark-brown, vein-limited spots. With time, these spots enlarged (up to 6 mm wide), often surrounded by a diffuse chlorotic halo. In severe attacks, leaves yellowed, withered, and dropped prematurely. Typically spots were more severe on mature leaves and progressed to younger leaves.

Microscopic examination of necrotic spots revealed clustered conidiophores in discoid white or pale acervuli produced subepidermally in concentric circles on both leaf surfaces. Conidiophores were simple, nonseptate, and short, slightly wider at the base than at the apex. Conidia were hyaline, filiform, straight or curved, mostly 3-6 septate, 25-58 µm long and 3-5 µm wide and were formed singly on conidiophores. The causal organism was identified as Phloeospora maculans (Bérenger) Allescher (=Cylindrosporium maculans) based on morphological characteristics (Sutton, 1980). The organism has been reported on mulberry in India (Pandey & Singh, 1989), Japan (Negi et al., 1992) and the US (McRitchie 1990). Pathogenicity tests were conducted on five mulberry seedlings (Morus alba cv. 'Beyaz Dut') with previously wounded (softly scratched with a sterile needle) or nonwounded leaves spray-inoculated with conidial suspension (5 x 10⁴ spores/ml). Inoculated plants were kept in a moist chamber (100% RH) at 25 °C for 3 days, then moved to a growth chamber at 22 °C with a 16 h photoperiod. Many small sunken necrotic lesions (1-2 mm wide) were noticed on inoculated leaves 5 days after treatment. These developed into lesions similar to those observed on naturally infected leaves, occurring on both wounded and nonwounded leaves 15 days after inoculation. The pathogen was reisolated from inoculated leaves. No symptoms developed on control plants.

We suspect that Phloeospora leaf spot has been present in the region for a few years, based on unconfirmed reports from silkworm farmers, but it has attracted little attention. Both mild winter temperatures and frequent spring rains during 2002 may have encouraged the epidemic outbreak of the disease. To our knowledge, this is the first confirmed report of Phloeospora maculans on mulberry in Turkey.