First report of Rhizoctonia zeae on Lolium perenne and Festuca sp. in Hungary

In August of 2002, brown patches were observed on turf grasses in parks and gardens at four locations within Budapest (Fig. 1). Twenty-five samples of Lolium perenne and Festuca sp. showing disease symptoms were collected. The symptoms observed were necrotic lesions on the roots and stems, as well as brown lesions on the leaves. The infected tissues were surface sterilised and plated on potato dextrose agar (PDA). The isolates were cultured at 22°C with a 12 h photoperiod. Most of the isolates produced fast growing, buff-coloured colonies, with dark brown sclerotia of irregular shape, not differentiated into a rind and medulla, with size range of 0.2 to 3.0 mm. These were identified as Rhizoctonia solani (Roberts, 1999; Sneh et al., 1991). Colonies from three samples were uncoloured-to-buff coloured, fast growing, with small, ball-shaped, reddish coloured sclerotia, 0.5 to 0.9 mm in diameter (Fig. 2). These were identified as R. zeae (Roberts, 1999; Sneh et al., 1991). The hyphae of both types of isolates were multiseptate and multinucleate (confirmed by nuclei staining).

Pathogenicity of one R. zeae isolate was determined on a mixture of Lolium perenne, Festuca rubra and Poa pratensis seedlings. Sterilised barley seeds, colonised with R. zeae and covered with pinkish to orange sclerotia of 0.5-2.5 mm diameter, were used as an inoculum (Fig. 3). Seeds of test plants were sown in a sandy loam soil admixed with barley seeds previously infected with the pathogen. Pots were then maintained in a greenhouse kept at a temperature of 16-32oC. Disease symptoms were observed three weeks after germination. Brownish lesions were observed on the infected seedlings at the base of stems and the lower parts of the leaves. Infected roots showed brown lesions and the leaves, on which orange sclerotia were found, were necrotic (Figs. 4, 5 and 6). Control plants grown in pots with uninoculated soil did not develop symptoms. R. zeae was reisolated from the diseased tissues (Fig. 7). In a host range study, our strain proved to be highly pathogenic to germlings of several ornamental and cultivated plants (e.g. Beta vulgaris subsp. vulgaris, Callistephus sinensis, Dahlia variabilis., Daucus carota, Lupinus polyphyllus, Papaver somniferum, Pennisetum glaucum, Phaseolus vulgaris, Sesamum indicum, Solanum melongena, Solanum tuberosum, Sorghum bicolor and Triticum aestivum).

The disease caused by R. zeae was described for the first time by Voorhees (1934) in Florida, as sclerotial rot of corn. This fungus is distributed in the temperate regions causing diseases on many plants, including Agrostis, Beta, Cucumis, Daucus, Festuca, Helianthus, Oryza, Sorghum, Triticum and Zea spp. This is the first report of R. zeae in Hungary.

This work is a part of a study supported by grant NKFP 4/008/2001