Ethephon, blast field resistance in rice

For the last several years Paul Counce has been part of a team studying blast resistance in rice.

“Research has shown when a variety very susceptible to blast — like Newbonnet — is flooded deeply and continuously, it becomes resistant to blast for the season,” says the rice physiologist at the Rice Research and Extension Center in Stuttgart, Ark. “By keeping it flooded, you're increasing resistance. Fleet Lee (a rice disease specialist heading the research) calls this ‘field resistance.’”

Some varieties tested with blast spores in the greenhouse are very susceptible. However, when carried to the field and flooded, the same varieties gain resistance. Cypress is one example.

“Our research group wanted to know why this is the case,” says Counce. “It turns out when you flood rice it must be able to feed oxygen into the roots. It does this by using ‘ethylene.’ When a flood is put on, the substance builds up and some of the cells in the roots begin dying. Those dead cells leave hollow tubes that allow air to reach the roots.”

Researchers wondered what would happen if ethylene was applied to rice. “Turns out, when we put ethephon (the active ingredient in cotton's Prep) on rice, it stimulates the plant and increases its resistance to blast. Ethephon is converted to ethylene in the plant.”

In essence, the rice plant is tricked into thinking it's flooded.

Some varieties have a gene resistant to blast. But that resistance can be overcome quickly if the blast fungus mutates.

The broad-spectrum field resistance induced by ethephon isn't easily beaten by the fungus, though.

“Using ethephon, we can reduce susceptibility to blast in a very susceptible rice variety that we don't grow in the South — like M-201 (a California variety). It still wouldn't have acceptable resistance in the South. We need to grow varieties targeted to this area. But the fact that we can induce resistance at all is exciting. I believe this will open new doors for rice research and farming.”

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