Evolution of rice breeding priorities based upon technology, industry needs

Rice Breeding Priorities 1JPG

Hundreds of rice seed samples are examined and distributed each year from the H. Rouse Caffey Rice Research Station for use in multi-location trials to test each line’s performance. Here rice breeder Adam Famoso assesses one of the latest samples to be tested. Photo by Derek Albert/LSU AgCenter

The H. Rouse Caffey Rice Research Station has been a crucible for rice variety developments for more than a century. Its evolving breeding objectives have fueled the development of varieties that help to retain the viability of the entire rice industry.

LSU AgCenter rice breeder Adam Famoso said that while breeding priorities have progressed with the needs of the industry, the main goals have remained the same during the 113 years that the Rice Research Station has existed.

“The major objectives haven’t changed, in terms of trying to develop varieties that support the sustainability and profitability of the industry,” Famoso said.

Rice breeding efforts at the station have led to the registration of 60 cultivars — the latest being Avant and Addi Jo. One of the researchers who has focused on variety development is Steve Linscombe, senior rice breeder and geneticist. The 1991 release of Lacassine marked the first rice cultivar that Linscombe was credited with creating. The list of rice varieties created under his leadership reads like a roll call of success stories. Bengal, Cypress, Cocodrie, CL161 (the first of many Clearfield lines), Chenier, Jupiter and Jazzman have become benchmarks of rice production. He said when the research facility was established in 1909, variety development efforts were based on adapting cultivars from around the globe to the southwest Louisiana rice industry.

“There was a variety of improvement efforts, but it wasn't so much rice breeding,” Linscombe said about the early 20th century rice research at the facility. “There was quite a bit of material brought in from Japan, some brought in from Korea and some from the other Asian countries.”

Linscombe said it was in the 1920s that new varieties were first developed from crosses at the Rice Research Station.

“They were trying to develop very high yielding varieties,” Linscombe said of his rice breeding predecessors. “They were trying to develop varieties with, primarily, disease resistance. There weren’t a lot of opportunities for looking at insect resistance at that time.”

Rice variety development then took a major leap forward with the release of the herbicides that were effective at killing weeds but would not harm rice. Developed in the 1940s, 2,4-dichlorophenoxyacetic acid, commonly known as 2,4-D, was the first herbicide that could be used in rice fields, but it only controlled broadleaf weed species. The early 1960s garnered the release, development and testing of propanil, a herbicide that could not only control some broadleaf species, but, most importantly, grasses.

“Up until that time, your varieties had to be very vigorous, very tall, because basically, they had to outgrow grass,” Linscombe said. “There was not anything that you could use to selectively eliminate grasses in rice fields.”

This single development, the release of a broad-spectrum herbicide for use in rice fields, was like a battering ram to the screen door of variety development. With grass competition no longer an issue, rice could be bred for shorter varieties that were more resistant to lodging. With less chances for lodging, producers could apply more nitrogen fertilizer in their fields which would create higher yields.

“That was a huge change in the way that rice breeders could now look for plant types with one event—the registration of one herbicide,” said Linscombe.

Rice breeding developments then progressed with an emphasis on rice grain quality in the late 1970s, Linscombe said.

“We were starting to develop a lot of international markets,” he said. “There were different demands on different qualities and different rice types. The breeders started doing more work with specialties, with aromatics. That has continued this day.”

With changing market demands, breeding priorities have continued to evolve, as well. Some aspects of rice grain qualities, such as amylose content, have shaped variety development efforts. Famoso explained most of the rice varieties typically contain intermediate amylose, which essentially defines southern-style long-grain rice varieties. But recent efforts to establish market shares in Latin American countries has fueled the development of high-amylose varieties, such as Addi Jo, which is set for a potential commercial release in 2024.

The other major change was a shift in grain length. Linscombe said in 1982, when he started his career with the AgCenter, the Louisiana rice industry consisted of 65% medium-grain cultivars with the remaining acreage in long-grain varieties. That has since changed, rather drastically. The veteran rice breeder said as the constituency of the industry changed, the focus of the breeding program changed with it. For 2022, 89% of the rice grown in Louisiana is long grain, while the remainder is medium grain.

While grain quality developments and herbicide technologies were effecting change, rice researchers were making selections for disease resistance. Now Famoso and his colleagues have grabbed the baton to move forward with the breeding program. Within the last decade the prevalence of blast resistance in new varieties has increased with the incorporation of the broad-spectrum blast resistance Pita gene. That discovery has allowed researchers to focus on other breeding priorities.

“We’ve made a lot of progress in the breeding programs on blast,” Famoso said. “So, it gives you time to focus on something else — like sheath blight.”

Over the last five to six years, with the help of emerging technologies, such as genetic markers, researchers have identified and isolated four other genes that stave off blast. This ensures that if Magnaporthe oryzae — the fungus that causes blast — mutates, there will be a built-in defense mechanism in varieties that contain at least one of those genes.

Famoso said choosing rice breeding priorities will continue to be based upon two things.

“It’s a balance between, first, the importance to the industry and the probability of success,” he concluded.

11/21/2022 5:24:15 PM
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