First Report of Peronospora farinosa f. sp. spinaciae Causing Downy Mildew on Spinach in Egypt

Downy mildew, caused by Peronospora farinosa f. sp. spinaciae (= P. effusa) is an economically important disease in most areas where spinach is grown. This disease has become increasingly important in intensive production fields for pre-packaged salad mixes where plant densities typically are very high (2). However, little is known about race diversity of the downy mildew pathogen of spinach in smaller (<1 ha) production areas. Small (~0.1 ha) spinach production fields in Fayoum, Egypt, often intercropped with lettuce, were examined in February 2013. Downy mildew was observed in three spinach fields in the Fayoum area. Most of the cultivars being grown were traditional cultivars commonly grown from locally produced open pollinated seed. Disease incidence was relatively low with only about 10% of the plants showing symptoms of infection. Symptoms of downy mildew were observed on the cultivar Meky, and included chlorotic spots with blue-gray sporulation on the underside of the symptomatic leaves. Microscopic examination revealed sporangia, measuring 20.2 × 30.5 μm, and monopodial sporangiaphores of 180 to 330 μm length matching the description of P. farinosa f. sp. spinaciae (1). In addition, the pathogen was identified by examination of the nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS) sequence, which had 100% identity to a 762-bp ITS sequence in GenBank of P. farinosa f. sp. spinaciae (Accession No. DQ643879.1). The Fayoum area of Egypt gets relatively low annual rainfall, typically <10 to 15 cm annually, often concentrated in the winter months of November to February, followed by very hot, dry summer months. Although downy mildew of spinach has been reported in Israel, adjacent to Egypt, the disease apparently is relatively rare in the arid Middle East (3). This is the first known report of downy mildew of spinach in Egypt. References: (1) Y. Choi et al. Mycol. Res. 111:318, 2007. (2) J. C. Correll et al. Eur. J. Plant Pathol. 2011. (3) T. Rayss. Palest. J. Bot. Jerusalem Ser. 1:313, 1938.