Sclerotium hydrophilum newly reported on rice in Turkey

In 2003 and 2005, routine disease surveys were conducted in rice (Oryza sativa) fields in Artvin and Samsun provinces, Turkey. In total, 41 fields were sampled from four districts. Distinct symptoms consisting of brown to black lesions that expanded and girdled the sheath were observed in one of the five fields surveyed in the Yusufeli district (Artvin), and two in each of the series of eight, 12 and 16 fields surveyed in the Alaçam, Terme and Bafra districts (Samsun), respectively.

Infected leaf sheaths were surface disinfected for one minute in 1% NaOCl, plated on potato dextrose agar (PDA) and incubated at 25° C. Colonies of pure cultures on PDA were white at first and then turned light brown or brown with increasing age. Four days after sub-culturing, large numbers of round or oval shaped sclerotia formed on the surface of the PDA, completely covering the culture (Fig. 1). The sclerotia were initially white, turning reddish brown to black upon maturity and measuring 276-597 (413) x 249-483 (352) µm (n=50). Two nuclei per hyphal cell were observed when the mycelium was stained with a mixture of Saffranin O and 3% KOH (Bandoni, 1979). Hyphal diameters ranged from 3.2 to 7.6 (5.1) µm. The fungus was identified as Sclerotiumhydrophilum Saccardo based on its micro-morphology and cultural features (Cedeno et al., 1997; Aye et al., 2009).

To satisfy Koch’s postulates, four week-old rice sheath tissues(cv. Osmancık)were inoculated with 4 mm diameter plugs of five-day-old cultures on PDA that contained mycelium and sclerotia. Sterile, noncolonized PDA plugs were used as controls. The plugs were covered with parafilm and the plants were maintained in a greenhouse. Symptoms, similar to those originally observed in the field, began to appear on the leaf sheaths after 14 days at 25º C (Fig. 2). No symptoms developed on control plants. The fungus was successfully re-isolated from the symptoms of artificially inoculated plants. Histological observations revealed brownish runner hyphae, and lobed hyphopodia were produced on the surface of infected leaf sheaths by S. hydrophilum(Fig. 3, 4). S. hydrophilum has been recorded previously on ricein Venezuela (Cedeno et al., 1997), in Australia (Lanoiselet et al., 2002) and in Myanmar (Aye et al., 2009). This is the first report of S. hydrophilum from Turkey.