<i>Ustilaginoidea virens</i> Infection of Rice in Arkansas: Toxicity of False Smut Galls, Their Extracts and the Ustiloxin Fraction

Abstract

Cool, wet conditions in the southern US during the maturing stages of rice in 1998 contributed to outbreaks of false smut caused by Ustilaginoidea virens. Water extracts of false smut galls in Asia have been reported to contain ustiloxin toxins, cyclic peptide antibiotics that interfered with microtubule function and caused "lupinosis"-like lesions in mice. Cell-free extracts from false smut galls on rice grown in Arkansas were fractionated by a published procedure for the purification of ustiloxins. The ustiloxin fraction was phytotoxic to Lemnapausicostata (duckweed) at ≥19 µg/ml, but the host plant, rice, was much less susceptible, exhibiting phytotoxic effects in germinating seeds at ≥1000 µg/ml. The aqueous extract of rice false smut galls showed no cytotoxicity to mammalian cell cultures at 200 µg/ml, but the ustiloxin fractionwas cytotoxic at 10 -100 µg/ml. However, rice false smut galls were not toxic when fed to mice at 10% of chow, but caused feed refusal at higher concentrations. We conclude that for 1) the U. virens which causes false smut in southern USA differs from Asian isolates in that does not produce detectable ustiloxins; and 2) false smut affects the appearance, but not the food safety of rice in the United States.

Seed Germination and Grain Quality of Rice as Affected by False Smut Disease

“…It is established that smut balls produce mycotoxins known as ustiloxins (Koiso et al, 1992). Ustiloxins are cyclic peptides, which are toxic to plants and animals by interfering with microtubule function, thereby inhibiting mitosis (Koiso et al, 1994;Abbas et al, 2014). Scientists, thus, raised concerns on direct impact of RFSm on seed germination and grain quality.…”

“…In addition, published reports indicate impact of the disease on seed quality attributes such as reduction in individual grain weights (Singh et al, 1992;Hegde and Anahosur, 2000;Srivastava et al, 2014). Abbas et al (2014) showed that variation in germination of the disease contaminated seeds was specific to rice varieties. There has been no report on the effect of seed germination in the RFSm contaminated seeds in Bangladesh.…”

Research on Advance of Rice False Smut Ustilaginoidea virens (Cooke) Takah Worldwide: Part II. Studies Progress on the Pathogen and Its Toxin of U. virens

“…Ustiloxins could inhibit the mitosis of garlic root tip cells, but it did not inhibit cell elongation . Abbas et al (2014) demonstrated that the extract of U. virens from Arkansas, USA, had almost no effect on rice seed germination, but it did exhibit toxicity to duckweed.…”

Development of rice conidiation media forUstilaginoidea virens

“…Frequently, sclerotia can be observed on the surface of false smut balls. In addition to yield losses, U. virens produces ustiloxins that are toxic to human and animals and can inhibit radicle and plumule growth in plant seedlings (Abbas 2014; Meng et al 2015; Wang et al 2017).…”