Brown patch (Rhizoctonia blight) of bristle basket grass in Mazandazan, Iran

Subject Areas : دو فصلنامه تحقیقات بیماریهای گیاهی

M.A Aghajani ¹ (استادیار پژوهش، بخش تحقیقات گیاه‌پزشکی، مرکز تحقیقات کشاورزی و منابع طبیعی استان گلستان، گرگان، ایران.)

Received: 2012-04-06 Accepted : 2012-09-12 Published : 2013-05-22

Keywords: Oplismenus hirtellus, bristle basket grass, Brown patch, Rhizoctonia blight, Rhizoctonia solni, AG1-IA,

Abstract :

"> The symptoms of brown patch or Rhizoctonia blight of bristle basket grass (Oplismenus
hirtellus) were observed in the summer of 2004 in a citrus orchard in Babolkenar region,
South of Babol, Mazandaran province. The individual plant symptoms consisted of blighted
spots, which gradually expanded to encompass the entire surface of the leaf. Patches of
affected grass had a diameter of approximately 20 to 100 cm. Dark brown sclerotia were
abundantly produced on the diseased plants and in soil.Plants started to recover and resumed
growth from the centre of the patch outward at the end of summer (because of the cooling of
the air), producing a ring pattern in the affected area. A multinucleate Rhizoctonia sp. was
consistently isolated from blighted tissues. Based on colony and mycelial characteristics, the
fungus was identified as Rhizoctonia solani, and the anastomosis group (AG) for most of
these isolates was determined as AG 1 by anastomosis testing. On the basis of cultural and
sclerotial characteristics, subset of the isolates was determined as AG 1- IA. The hyphal
diameter of the isolates was 7.0 5m, and the mean number of nuclei was 6.4 per hyphal cell.
The colony was light brown on potato dextrose agar after 2 weeks of growth, and dark brown
sclerotia measuring 0.7 to 4 × 1 to 4.5 mm were abundantly produced on the medium.
Cardinal temperatures for growth of this isolate were 10, 28, and 35°C. The linear growth rate
at the optimum temperature was 34 mm per day. Pathogenicity of the AG 1-IA isolate was
confirmed by placing 8-mm disks from the margins of an actively growing colony on the
leaves and sheaths of the host plant. Symptoms observed were the same as those in the field,
and the fungus was reisolated from the blighted tissue. To our knowledge, this is the first
report on the occurrence of brown patch disease of O. hirtellus in Iran. The bristle basket
grass is introduced as a new host for R. soloni in Iran.

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