Title: Ustilaginoidea virens infection of rice in Arkansas: Toxicity of false smut galls, their extracts and the Ustiloxin fraction Authors
|Shier, Thomas -|
|Cartwright, Rick -|
|Sciumbato, Gabe -|
Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2014
Publication Date: N/A
Interpretive Summary: A disease called false smut occurs on grain crops such as rice under cool, wet conditions in US and Asia. This disease is caused by a mold called Ustilaginoidia virens. In Asia, the false smut galls produce toxins called ustiloxins which cause are toxic to plants, animals and possibly humans; therefore, this disease decreases the value of rice or other grains because of potential toxicity to people and animals, and reduced value due to discoloration. We determined that the strain of this mold of false smut found in US did not contains these toxins. This is reassuring to the US population and shows that even contaminated rice crops are not dangerous to use as food and feed in this country and abroad. This information will be useful to farmers and industry when they are confronted with an outbreak of this disease in rice.
Technical Abstract: Cool, wet conditions in the southern U.S. 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 Lemna pausicostata (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 fraction was 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 (i) the U. virens which causes false smut in southern USA differs from Asian isolates in that does not produce detectable ustiloxins; and (ii) false smut affects the appearance, but not the food safety of rice in the United States.