Natural Fungicide May Blast Global Rice Disease

Rice blast, the most important fungal disease of rice plants worldwide, and other diseases may some day be controlled by a natural fungicide produced by a specially fed bacterium collected from a central Illinois hog farm.

The U.S. Department of Agriculture has applied for a patent on the bioconversion process developed by Agricultural Research Service scientists at the National Center for Agricultural Utilization Research (NCAUR), Peoria, Illinois. ARS is USDA’s chief scientific research agency.

The bacterium, a strain of Pseudomonas aeruginosa, was found in hog manure. The strain converts ricinoleic acid to the new fungicidal compound, 7,10,12-trihydroxy-8 (E)-octadecenoic acid (TOD). Ricinoleic acid is a major component of imported castor oil, but someday it may be economically made from oil of genetically modified oilseeds such as U.S-produced soybeans. Castor beans are produced primarily in India.

In a laboratory batch process, the P. aeruginosa strain converted up to 45 percent of ricinoleic acid into TOD. Scientific collaborators of a major chemical company sprayed rice plants with a dilute--5 parts per million--solution of TOD and inoculated the plants 24 hours later with Pyricularia grisea, the fungus that causes rice blast. Five days after the inoculations, sprayed plants had only about 29 percent as much fungal growth as unsprayed plants.

Now the scientists are researching ways to scale up production of TOD for further experiments on P. grisea and other fungi and insect pests of crops and stored products. Laboratory tests, using the dilute solutions, so far have also shown inhibition of fungi that cause rice sheaf blight and peach blossom blight.

The P. aeruginosa strain is one of more than 80,000 microbial strains of potential agricultural and industrial importance maintained in the ARS Culture Collection (NRRL) at NCAUR in Peoria.

Scientific contacts: Ching T. Hou and Tsung Min Kuo, ARS National Center for Agricultural Utilization Research, Peoria, Ill.; phone (309) 681-6263, fax (309) 681-6686, houct@ncaur.usda.gov, kuotm@ncaur.usda.gov.