Rice Farming

CA Breeders Address Disease

Researchers make progress with resistance
through genetics

By Brenda Carol

Incorporating genetic disease resistance into premium California rice varieties is a never-ending research endeavor at the Rice Experiment Station (RES) in Biggs, Calif. Researchers are constantly trying to develop varieties with resistance to blast, sheath spot and stem rot diseases, which can substantially lower the state’s production. Often, disease problems in rice are limited in scope, but can be significantly problematic when they occur.

Rice researchers have made significant progress over the past few years addressing disease resistance through genetics, according to Jeff Oster, RES plant pathologist. Virgilio Andaya, RES plant breeder, has also been working on the integration of molecular marker technology and genomics tools with conventional breeding methods to develop improved rice varieties. Molecular markers speed the development of new resistant varieties. Breeders can use the technology to identify resistant genes from different backcrosses and quickly eliminate backcrosses that are not promising.

Researchers search for more blast-resistant genes
Breeding for blast resistance has been one program that has proven very successful. While the disease is not necessarily widespread, it can be devastating.

“The variety M-208 was released in 2005 and includes blast resistance from the major gene Pi-z obtained from the Southern medium grain variety Lafitte from LSU AgCenter,” Oster says. “M-208 was the second blast-resistant variety released in California.”

It is an early maturing, semi-dwarf, glabrous, Calrose medium- grain (CRMG) quality rice variety with Pi-z gene resistance to race IG-1 of the rice blast pathogen found in California. The release of M-208 is a key factor in keeping blast under control in California.

“Blast is still mostly restricted to certain microclimates and may be successfully controlled by planting M-208,” says Chris Greer, Sutter and Yuba Counties farm advisor.

Even so, breeders are still looking for additional blast-resistant genes to add to the germplasm pool. Seven lines have been imported from the International Rice Research Institute (IRRI) that confer broad-spectrum race protection. However, the tricky part of the backcross equation is making sure blast-resistant genes can be incorporated successfully into California varieties, according to Oster. Researchers are looking at the possibility of obtaining blast-resistant genetic traits from wild species of rice originating in other areas of the world. California’s production is dominated by short- and medium-grain japonica varieties.

“We’re looking at indica, as well as other donor varieties that cannot make it here in California due to poor seedling vigor, poor cold tolerance or other characteristics,” Oster says. “In those cases, we’re backcrossing to extract the genes we want out of the donors and put them into something that works in California rice.”

The next goal is to incorporate the yield and quality characteristics of California’s M-206 variety into M-208 while maintaining blast resistance. Even if accomplished, it will almost assuredly be a race against time.
“Resistance usually breaks down within two to three years after a variety is released,” Oster says. “We need to have a backup in case blast flares up again.”

Stem rot resistance in medium-grain varieties
Stem rot is another issue California researchers are addressing.

“It’s different than blast in that it cannot spread rapidly over wide acreages and cause multiple cycles of disease,” Oster says. “It just lingers in areas where it’s adapted and can cause up to 25 percent yield loss. Medium grains are particularly susceptible to problems.”

Long-grain and short-grain varieties have been successfully bred with resistance to stem rot disease, but breeders have not been able to incorporate that protection into the medium-grain program in California. However, a backcross program for stem rot resistance in medium grains, initiated in 2005, looks promising. The resistant stem rot gene was derived from long- and short-grain high yielding varieties and is being incorporated into the M-206 background.

Sheath spot
Sheath spot resistance is another issue rice breeders are tackling, but do not yet have the molecular markers to aid the process. Sheath spot is not as damaging as stem rot under most California conditions, but it’s still a concern. Sheath spot is similar to sheath blight in Southern states. Efforts to incorporate resistant genes from the indica race into the japonica race grown in California have proven difficult. Although it is a lower priority, it’s still important, according to researchers.

“You’re probably looking at a 5 to 10 percent yield loss from sheath spot when you have dew on the plants for an extended period of time,” Oster says. “It’s sporadic. You don’t see it every year, but if you can build resistance in the plant, you don’t have to monitor, and you don’t have to worry about spraying.”

Another lesser concern is bakanae. Affected plants are infertile with empty panicles and often lodge and die.
“Bakanae is pretty well managed using the Clorox seed soak,” Greer says.

Bakanae is a seed-borne disease. “If you can eliminate the pathogen on the seed, it doesn’t persist very well over the winter,” Oster says.

At this point, rice breeders are focused on California’s “hot spots.”

“Stem rot and aggregate sheath spot remain the most widespread and prevalent diseases,” Greer says. “Hopefully, we do not have any new introduced pathogens in the next few years.”

Brenda Carol is a freelance writer based in California. Contact her at (805) 226-9896 or brenda@brendacarol.net.


Farmers prepare for water cutbacks

No one really has a clue what’s going to happen in 2009 in terms of water allocation in California. No one even has a clue what relief March rain and snow will bring at this point. What is certain is that December, January and February hurt like a dehydrated Delta smelt fish. Although recent precipitation going into March has prompted some optimism, no grower in the state of California is declaring “water emergency over.”

“We are still in a drought mode,” says Randall (Cass) Mutters, Butte County farm advisor in Oroville, Calif. “The governor declared a drought state of emergency in late February. The snow pack is still below normal.

What the actual water deliveries will be is still in a state of flux. Two local districts here are, thus far, sticking to their earlier call of less than 50 percent of normal delivery. We probably won’t get a final call until April.”
California’s Department of Water Resources’ (DWR) third snow survey of the winter season indicates snow water content is 80 percent of normal as of March 2, 2009, statewide.

“On the heels of two critically dry years, it is unlikely we will make up the deficit and be able to refill our reservoirs before winter’s end,” says DWR director Lester Snow.

Governor Schwarzenegger’s declaration of a drought state of emergency in late February directed DWR and other state agencies to provide assistance to people and communities impacted by the drought. That begs the question: What can California rice growers do to conserve water? The answer: Probably not much, since they are already conservative due to measures implemented over years of boom and bust when it came to water availability.

“Improved varieties and advances in technology, such as laser leveling of fields, have improved water efficiency in rice fields by approximately 30 percent in the last three decades,” says California Rice Commission communications manager Jim Morris.

Ultimately, in California, water delivery is based on precipitation in the state, but who gets what is largely political. Many growers (not just rice growers) may have to go underground in 2009 just to keep crops alive. It’s widely speculated that row-crop plantings will suffer at the expense of trying to keep permanent crops viable. Growers lucky enough to have access to well water are, in some cases, more worried about the quality of that water as compared to surface water that flows relatively pure from the mountains.

“Growers are preparing to supplement deliveries with well water,” Mutters says. “I have not heard any rumbles that growers in mass are planning to change water management, although it would be a good idea to explore possibilities.”