S. Soylu*, E.M. Soylu and S. Kurt

Department of Plant Protection, University of Mustafa Kemal, Faculty of Agriculture, 31034 Hatay, Turkey.

*soylu@mku.edu.tr

Accepted for publication 19/05/03

In February and November 2002, a severe outbreak of a foliar disease was noted in the major Swiss chard (Beta vulgaris L. var. cicla) fields in the Hatay province of Turkey. In this region, disease was observed in 90 to 95% of fields inspected. Symptoms began as small circular, light brown spots with definite dark brown border on both sides of the leaf. The circular spots increased in size (up to 4-6 mm in diameter), developing into depressed lesions, which were brownish in color and bordered by a purple margin (Fig. 1). As lesions matured, the centre of the spots became whitish grey to black, due to the production of conidia and conidiophores.

Figure 1. Typical leaf spots caused by C. beticola on Swiss chard leaf (Left hand picture), along with a close up of a typical leaf spot (Right hand picture).

Microscopic examination of the whitish-grey lesions revealed the presence of tiny, black stromata within the leaf substomatal cavities. The stromata produced dense fascicles of conidiophores (up to 35 conidiophores per fascicle) that emerged through the stomata (Fig. 2). Conidiophores were simple, 1 to 3 septate, pale brown at the base but subhyaline at the apex, straight (3.5-4.5 x 20-65 µm), unbranched and slightly attenuated towards to apex. Conidia, borne singly, were filiform, hyaline, pluriseptate (5 to 18), non-constricted at the septa, slightly curved, subtruncate at the base, obtuse to subacute at the apex and varying considerably in length (2.5-4 x 40-125 µm). The causal organism was identified as Cercospora beticola Sacc. based on morphological characteristics (Kim & Shin, 1998). A single-spore isolate was cultured on V-8 juice agar. Pathogenicity tests were conducted on 4 week-old chard seedlings (cv. Zilk), by spraying the leaves with a conidial suspension (10⁴ spores per ml). Inoculated plants were kept in a moist chamber (100% RH) at 25 ^oC for 3 days, then moved to a growth chamber at 26 ^oC with a 16 h photoperiod. Many small elongated lesions (1-2 mm wide) were observed on inoculated leaves 5 days after treatment. After 21 days, these developed into lesions similar to those produced on naturally infected leaves. The pathogen was reisolated from inoculated leaves.

Figure 2. Fascicles of conidiophores emerging through stomatal openings and formation of conidia.

This is the first report of C. beticola on Swiss chard in Turkey. Previous reports list C. beticola on Swiss chard in Egypt (El-Kazzaz, 1977) and Korea (Kim & Shin, 1998). C. beticola was also reported on several host plants such as cultivated and wild Beta spp., spinach and lambs quarter (Nyvall, 1989; Rossi et al., 1995).

El-Kazzaz MK, 1977. Cercospora leaf spot disease of chard in Egypt. Egyptian Journal of Phytopathology 9, 81-82.

Kim JD, Shin HD, 1998. Taxonomic studies on Cercospora and allied genera in Korea (II). Korean Journal of Mycology 26, 342-353.

Nyvall RF, 1989. Field crop diseases handbook. New York: Van Nostrand Reinhold.

Rossi V, Racca P, Giosue S, 1995. Geophytopathological analysis of Cercospora leaf spot on sugar beet in the Mediterranean area. Phytopathologia Mediterranea 34, 69–82.

The British Society for Plant Pathology