Beet breeders develop international partnership

Adam Sitarski (left) and Imad Eujayl look over sugar beet plants in a recent disease trial at the Kimberly Agricultural Research Service greenhouse.

The search for a sugar beet that can produce high sugar while warding off disease has led a Kimberly researcher to Poland.

Developing a sugar beet variety that can produce more than 20 percent sugar has long been a goal of beet breeders in the U.S. Beets in Idaho averaged around 17 percent sugar this year.

But growers in Poland consistently harvest beets with more than 20 percent sugar thanks to a long tradition of breeding for high sugar content. Beet breeding in the eastern European country dates back 130 years. Research suffered during the Communist years when contact with the outside word was limited but breeders maintained lines. Once Poland joined the European Union, research flourished again.

Even though cooperation between countries has improved, accessing Poland’s high sugar germplasm has remained a challenge for U.S. breeders, as Imad Eujayl discovered.

Eujayl is a research molecular biologist with the Agricultural Research Service in Kimberly. His work has focused on developing disease resistance to common problems in Idaho including rhizomania and curly top. But he knew growers needed high sugar production in addition to disease resistance.

“Access to a source of high sugar germplasm is simply not here (in America),” Eujayl said.

Searching for sources of high sugar germplasm led him to a Kutno Sugar Breeding Co., a government-owned beet breeding company in Poland, and to Adam Sitarski, a fellow plant breeder.

Kutno focuses on using doubled haploid plant breeding to quickly develop pure lines for research. Doubled haploid is a common breeding technology in cereal grains where the plants rely on thousands or even millions of pollen grains to reproduce.

Diploid plants have equal chromosomes from both parent lines. A doubled haploid occurs when all the chromosomes in the seedling are from one parent. This can happen spontaneously in nature, leading to new colors of vegetables for instance. About 50 years ago researchers learned how to artificially develop doubled haploid plants in the laboratory allowing them to develop homozygous or pure lines in two generations compared to seven or more in traditional breeding.

“Using 100 percent homozygous plants is highly important for beet breeding,” Sitarski said.

While doubled haploid breeding is commonly used in grain breeding, sugar beets are less amenable to the technology thanks to a reproductive structure that relies on one flower and one ovule. Beets have a limited number of flowers compared with grains which makes doubled haploid process much more expensive for beets, Eujayl explained.

Sitarski has developed a successful process and Eujayl saw it as a way to bring high sugar germplasm to the U.S. The first challenge was developing a germplasm exchange agreement. Eujayl first contacted Sitarski in 2013 and then visited Kutno in 2014.

Once the paperwork was completed the next challenge was figuring out how to send 144 tiny carrot-like plantlets in petri dishes from Poland to Idaho. The first shipment was set to arrive through Seattle at Christmas 2015.

“I was panicky,” Eujayl said. He was afraid that the plantlets could freeze while waiting for inspectors to check the shipment or if the delivery truck was delayed.

Thankfully the plantlets did not freeze but they were susceptible to rhizomania. Despite suffering a high infection rate, the resulting plants still produced 19 percent sugar — 2 percentage points above Idaho’s average.

Those plants have been crossed with lines that have curly top and rhizomania resistance. Eujayl has identified two lines with high sugars and moderate curly top resistance that could potentially be commercialized.

“When it (the seed) goes to the field, everything changes,” Eujayl said. “For us, 19 percent sugar is very difficult to reach.”

In Poland, Kutno is using lines from Eujayl’s program to add rhizomania resistance to their traditional varieties.

The two collaborators have developed a strong working relationship over the last four or five years. Sitarski stopped by the Kimberly facility when he came to the U.S. last summer for a plant breeding academy held in California.

Even though doubled haploid breeding has significantly shortened the time to develop new lines, it is not a guarantee. Sitarski said some lines won’t produce haploid plants at all while others produce as many as 20 percent haploid plants. The average is 1 to 2 percent.

“Even you don’t know if you will be successful,” Sitarski said. “You may have nothing.”

Or you may have a parent line that has high sugar and is disease resistant.

“When it (the seed) goes to the field, everything changes. For us, 19 percent sugar is very difficult to reach.” Imad Eujayl, research molecular scientist at Agricultural Research Service in Kimberly