Scanning Electron Microscope reveals spined conidia of Ustilaginoidea virens.

Abstract

False smut of rice is caused by a fungal pathogen, Ustilaginoidea virens (Cooke) Takah. The disease has emerged as an increasing concern for rice production and pathologists since the widespread cultivation of hybrid rice and heavy application of nitrogenous fertilizer (Zhou et al 2008). The fungus transforms the infected grains into a yellowish smut ball, which gradually changes to yellowish orange, green, olive green and finally to greenish black. The smut balls are often enclosed by sclerotia that ultimately fall to the ground, leaving plenty of powdery chlamydospores. False smut balls on rice panicles are the typical symptom of the disease. The chlamydospores are almost smooth when young, and become warty when mature. Under bright-field light microscopy, the conidia are round to elliptical but under scanning electron microscopy, the globose to irregularly rounded conidia are ornamented with prominent spines. The spines are pointed at the apex or irregularly curved, and approximately 359.9-994.5 nm long (Baite et al 2014).