January 17, 2003
From: British Soc Plant Pathol, New Disease Reports, Vol. 8 [edited]

First report of powdery mildew caused by _Podosphaera phaseoli_ (syn. _Sphaerotheca phaseoli_) on cowpea (_Vigna sinensis_ L.) in Turkey
EM Soylu, S Soylu <soylu@mku.edu.tr>, S Kurt (Department of Plant Protection, University of Mustafa Kemal, Faculty of Agriculture, 31034 Hatay, Turkey).
Accepted for publication 7 Jan 2004.

During the summer of 2003, typical symptoms of powdery mildew were observed in many cowpea fields in Hatay Province, Turkey. White, epiphytic mycelia and conidia, characteristic of a powdery mildew, were present on leaves, stems, and inflorescences. The plant tissue underneath the mycelial patches was purplish in colour.

Mycelial growth was amphigenous, thick, forming irregular white patches, sometimes effused to cover the whole leaf surface and had a poorly developed nipple-shaped single appressorium. Simple straight conidiophores (115-190 x 10-13 micrometers) developed mostly singly from a hyphal cell, arising from the upper part of mother cells, and having the basal septum at the branching point of the mycelium with a sharp constriction.

Each conidiophore had 3 to 8 barrel-shaped conidia formed in a chain. Conidia with fibrosin bodies were 28-42 x 15-18 micrometers in size and germinated below the shoulder by producing a simple germ tube. Dark brown ascomata, found on leaves and stems as embedded in the mycelial felt, were spherical, gregarious to subscattered and measured 85 to 105 micrometers in diameter. Appendages (6 to 15) were myceloid, arising from the lower half of the ascomata, brown, paler upward and 6 to 8 micrometers wide.

The ascomata contained single ascus (65-95 x 55-67 micrometers). The ascus contained 8 ellipsoidal to ovoid ascospores (18-24 x 12-16 micrometers). On the basis of morphological characters of the conidial stage and teleomorph, the fungus was identified as _Podosphaera phaseoli_ [Pp] (syn. _Sphaerotheca phaseoli_) (Braun & Takamatsu, 2000; Shin, 2000).

Pathogenicity tests were conducted on 4-week-old cowpea plants, cv. Libye, by shaking fresh conidia from naturally infected plants onto healthy leaves. Inoculated plants were kept in a moist chamber (100 per cent RH)
for 2 days and then maintained in a growth chamber at 22 ± 2 deg C, 75 per cent RH with a 16 h photoperiod. After 7 to 10 days, inoculated plants developed powdery mildew symptoms similar to those observed on naturally
infected plants.

This is the first report of powdery mildew on cowpea in Turkey. Previous reports list Pp on _Vigna_ spp. in Korea (Shin & La, 1992; Lee et al., 2002). Pp was also reported on several related host plants such as _Phaseolus spp_. and _Rhynchosia volubilis_ (Shin, 2000).

Although bean is one of the alternate hosts of Pp and grown in nearby cowpea plants in the same field, no disease symptoms were observed on bean.

References
Braun U, Takamatsu S. Phylogeny of Erysiphe, Microsphaera, Uncinula (Erysipheae) and Cystotheca, Podosphaera, Sphaerotheca (Cystotheceae) inferred from rDNA ITS sequences - some taxonomic consequences.
Schlechtendalia 2000; 4: 1-33.
Lee SY, Hwang SJ, Lee SB. Occurrence of powdery mildew on mung bean (Vigna radiata L.) caused by Sphaerotheca phaseoli. Research in Plant Disease 2002; 8: 166-70.
Shin HD. Erysiphaceae of Korea. Suwon, Korea: Nat Inst Agric Scie Tech, 2000. Shin HD, La YJ. Addition to the new records of host plants of powdery mildews in Korea. Korean Journal of Plant Pathology 1992; 8: 57-60.

[I could not find any information relevant to this disease or its management. The disease has not been reported previously in ProMED-mail; this piece is being posted for the record. Further information would be welcomed. - Mod.DH]