Host range of Rhizoctonia zeae in Iran.
In summer and autumn 1998 and 1999, during a survey for diseases of Gramineae in the central regions of Mazandaran province (Iran), a seemingly new disease was observed in sugarcane (Saccharum officinarum) fields at Babol, Babolsar, and Sari, with an incidence of up to 90%. Cream-to-light brown lesions with a purple-to-dark brown border, surrounded by a deep orange-to-red halo were observed on leaf sheaths and stems up to 50 cm above the ground. A second broad orange halo was present at the periphery of the lesions on the leaf sheath. A loose web of fungal hyphae occurred under the sheath and, sometimes, lateral stems were rotten. An orange multinucleate Rhizoctonia was consistently isolated from the infected tissue, which produced minute reddish orange sclerotia on and within potato dextrose agar (PDA), after 10-14 days of growth. Based on cultural, morphological, and growth characteristics, this fungus was identified as Rhizoctonia zeae [Waitea circinata]. The same fungus was also isolated from the soil and from sheath and culm tissues of Zea mays, Sorghum bicolor, Sorghum vulgare var. sudanense [Sorghum drummondii], Sorghum halepense, Cynodon dactylon, Saccharum ravennae and Eragrostis barrelieri. Pathogenicity tests were conducted and within 1 week from inoculation, lesions began to appear in all hosts, from which the fungus was consistently reisolated. This is thought to be the first report of R. zeae from Iran. All plant species mentioned above, except for of Z. mays and Sorghum halepense, are new hosts (matrix nova) for R. zeae.