Biology and Control of Rice False Smut Caused by Ustilaginoidea virens (Teleomorph Villosiclava virens)

Rice false smut (FS), a disease caused by Ustilaginoidea virens (Cke.) Takahashi (1896), was first reported in northeastern Arkansas counties in 1997. The first objective of this research was to establish a collection of U. virens isolates from geographically diverse regions of Arkansas. Three U. virens isolates and chlamydospores from 'Templeton' and 'Clearfield-151' rice cultivars were used to determine the effects of temperature and pH on mycelial growth and germination. A nested-PCR protocol and histological methods were used to determine if U. virens infects and colonizes rice seedlings and spikelets on panicles. The sensitivity of three U. virens isolates was tested to analyze the inhibition of mycelial growth in vitro and to establish inhibitory concentrations to six technical and five analytical grade fungicides. Field and greenhouse tests were conducted to determine if fungicide seed treatments using technical grade fungicides could effectively reduce the incidence of U. virens rDNA in seedlings as measured by nested-PCR. Finally, field tests were conducted using fungicide seed treatments to control FS at two locations and disease was assessed by a visual disease assessment.;We have an established collection of 190 isolates obtained from nine cultivars in seven counties of Arkansas, USA. Mycelial growth and germination of chlamydospores occurred between pH levels from 5.5 to 8.0. Mycelial growth and germination of chlamydospores occurred at temperatures from 18° to 34°C and from 18 to 26°C, respectively. Nested-PCR tests indicate the protocol is specific and sensitive for detecting U. virens in rice. Ribosomal DNA of U. virens was detected using nested-PCR from seedlings within three days after emergence from the soil and in 27.5 to 75% of spikelets in booted panicles before exsertion. Selected isolates of U. virens were sensitive to fungicides in vitro but results from using nested-PCR in the greenhouse and field to screen seedlings for U. virens rDNA indicated a significant reduction in the incidence of U. virens in some seed treatments compared to controls. Seed treatments did not significantly reduce FS disease compared to controls in the field plots when measured by visual disease assessments.