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Bakanae threat leads to quarantines

Thankfully, Bakanae or “foolish seedling disease” isn't in Southern rice fields. The fungal disease is, however, in California rice, and both Arkansas and Louisiana have made moves to keep it out of the Mid-South.

The biggest concern, say those interviewed, is how Bakanae would respond in the South. “Our environments are probably more conducive for this disease and, if we got it, could lead to more problems than they're seeing in California,” says Steve Linscombe, Louisiana Extension rice breeder. “I agree with quarantines. We need to do everything to keep Bakanae out.”

Rick Cartwright, Arkansas Extension plant pathologist, agrees. “At the least, we don't want some routine route of introduction,” he says. “A quarantine is a reasonable path of action. Unfortunately, you can't ever prevent smuggling of seed — that may be how California got it in the first place. Many pathogens are introduced that way. But we can at least help prevent the disease coming in through normal channels.”

To prevent the disease spreading, Louisiana has had a quarantine on California rice seed for a year. At its next meeting, the Arkansas Plant Board will discuss enacting a similar quarantine.

“Any research seed we bring in from California is put through a greenhouse quarantine,” says Linscombe. “We do that already for varieties we bring in from around the world.

“Since it's such a small amount we're bringing in, we haven't put together any protocols for hot water treatment or those types of things. Down the road, that may change.”

While the issue is important, it isn't something dealt with constantly: there just isn't a lot of California rice seed coming into the South. In the past, the concern was more acute because some Southern producers were growing short grain varieties for specific markets.

With the recent release of Pirogue, however, the need to import such short grain varieties diminished.

“Releasing Pirogue — a short grain with agronomic characteristics for Louisiana — helps ease our minds about Bakanae,” says Linscombe. “That wasn't the main reason for the release, but it is a happy byproduct.”

Despite coffee-shop talk to the contrary, Bakanae isn't comparable to the Asian soybean rust issue, says Don Groth, plant pathologist at the Rice Research Station in Crowley, La.

“Bakanae isn't as explosive an issue, as dangerous as a disease. However, it is serious and is going to be difficult to keep out. Unfortunately, I believe there's a high probability that, sometime in the next five to 10 years, Bakanae will show up in the South. I believe it'll get here somehow.”

One thing to watch, says Groth: California rice grain can be brought to Arkansas and Louisiana for milling.

“That's a real avenue for Bakanae. Typically, rice hulls are taken out of the mills and dumped, often next to rice fields. Since Bakanae lives on rice hulls, that practice isn't conducive to keeping the disease out.”

Bakanae is a seed-borne fungus (a fusarium). The fungus produces gibberellic acid that makes rice seedlings and plants elongate. In severe cases, the rice will be killed.

“As Bakanae-infected plants develop through the season, fields will take on the look of red rice infestation,” says Groth. “Bakanae attacks basically all parts of the plant throughout the season.”

The infection easily carries over from season to season. A trace of Bakanae in a field one year can lead to 50-plus percent infection the next.

“Bakanae can build up in a crop incredibly fast,” says Chuck Wilson, Arkansas Extension rice specialist. “Plants infected with this grow very tall and thin at the seedling stage. At the three- or four-leaf growth stage, such plants can be a foot tall. Compare that to a healthy plant that, at that age, will be 4 or 5 inches tall. A field with Bakanae will be uneven throughout the growing season.”

The seed-borne disease has been in Japan for a long time, says Wilson. Until found in California a few years ago, it hadn't been documented in the United States.

The toxin the Bakanae organism produces may sound familiar. Gibberellic acid is used in rice as a seed treatment to enhance emergence. Used in small quantities, it's effective, causing plants to elongate temporarily. Once the supply of the acid is consumed, the plants continue to grow normally.

Last year, scares in both Arkansas and Louisiana brought the Bakanae threat into focus.

“We looked at a few fields last year that had Bakanae-type symptoms,” says Wilson. “At first, we were extremely worried that Bakanae had found its way here. After some intensive investigations, we narrowed the problem down to a contamination in the seed-treatment process. Some seed had received excessive rates of the gibberellic acid. Bakanae was ruled out as a suspect.”

“Yeah, we thought we had it — but it turned out to be a false alarm,” says John Saichuk, Louisiana Extension rice specialist. “Bakanae is definitely on our radar screen now.”

If not dealt with properly, Bakanae-related yield losses can be substantial. In Japan, yield losses of 20 to 50 percent have been observed. In India, yield damage of 15 percent has been reported.

“There aren't a lot of fungicides or control practices available to control it,” says Groth. “Once you have it, it's hard to get rid of. Producers here could probably manage the problem, but it will add cost and time-consuming steps to growing the crop that no one wants to deal with.

“What we must realize is the quarantines are aimed at stopping a single, limited event from happening,” Groth continues. “With all the ways seed is moved around, preventing Bakanae from ending up here will be difficult. But we've got to be careful and try.”


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