According to a study by the University of Idaho, potato bruising costs the U.S. potato industry nearly $300 million per year. Some experts attribute 60 percent of potato bruising to blackspot bruise. This condition is especially prevalent in Russet Burbanks, the most widely grown potato in the U.S.
Blackspot bruise is not the result of a virus or pathogen. It is a postharvest problem caused by a fall or hit to the potato. The tuber responds by releasing polyphenol oxidase, an enzyme that turns the points of impact black. Despite its unattractive appearance, the bruise on a potato is safe for human consumption.
However, because U.S. consumers desire appealing produce, potato processors spend money removing the bruises from tubers before cutting them into french fries or chips. Their quality standard includes cosmetic appearance. Because it costs processors extra to cut the bruises out, they pay growers on a sliding scale called Bruise Free, lowering the price per pound for bruised potatoes.
Keith Esplin, former director of Potato Growers of Idaho, is currently involved with Naturally Enhanced United Seed (NEU Seed), a cooperative of potato seed growers that formed in November 2008 to develop and market potato cultivars with new innovative traits for growers, processors and consumers. Although organic growers have said consumers should understand organic produce frequently looks imperfect, Esplin explains, “The reality is, consumers expect it to look pretty and not have blemishes.”
NEU Seed has formed an alliance with a California-based biotech company that aims to address the problem of blackspot bruising by altering potato seeds. By altering a single gene within the potato genome, plant biologists can turn off the enzymatic response that creates bruising.
In 2008, Cibus Global, a plant-trait development firm, partnered with NEU Seed to develop and market improved traits in potato using Cibus’ natural smart breeding tool, Rapid Trait Development System (RTDS). Initial work is focused on reducing blackspot bruising, with the aim of improving both productivity and the overall quality of potatoes available to the consumer. Esplin says once they have created a Russet Burbank that resists blackspot bruising, NEU and Cibus want to engineer tolerance to herbicide.
The worst weed problem growers have in many areas of the country is nightshade. This species of Solanum is a relative of potatoes, which makes it difficult to kill. Through natural selection, the weed has grown stronger and more resistant to the herbicides growers use to control them. Nightshade also hosts multiple diseases and attracts aphids. Aphids are a vector for spreading diseases, like leaf roll virus and PVY virus, and the insects multiply even faster on the weed than on the potato plant. Using multiple applications of herbicide is especially problematic for seed potato growers. Because potatoes are grown clonally, they carry viruses from one crop to the next. Seed growers must be extremely careful to keep viruses out of their production. Esplin believes engineering herbicide tolerance via RTDS will make it easier for growers to control the nightshade weeds. “Growers will have the benefit of better weed control, once the potatoes are herbicide-tolerant.”
Why scientists and growers believe RTDS will work
Traditionally, to create new varieties, potato breeders rely on the flower for production. Russet Burbank seeds are mostly sterile, which makes traditional breeding challenging. When potato varieties are crossed, the results are unpredictable. Breeders must screen out the duds, but are limited because they can grow only one crop of seed per year. Ultimately, it can take 15 to 20 years to produce a new variety.
Esplin says when he learned about Cibus’ directed mutagenesis process at a National Potato conference in 2007, he was immediately interested. RTDS is a trait development procedure that uses the plant’s natural process of gene repair to effect a precise change in the genetic sequence. RTDS has proven itself in the laboratory and in initial field trials of Cibus’ first commercial crop, canola. By mimicking natural methods in a highly targeted way, RTDS technology avoids the introduction of foreign genetic material into plants, a method characteristic of genetic engineering. Recognized by the USDA as a mutagenesis technique, RTDS is not subject to the regulations applied to transgenic (or GM) crops. “It’s a way that can bring traits into the market that’s acceptable and natural,” says Esplin. “They can only do what could happen naturally.”
During his tenure with Australia’s Department of Agriculture, Dr. Peter Beetham, now senior vice president of research at Cibus Global, examined viruses and diseases affecting root crops. Focusing mainly on potato and sweet potato, Beetham learned that by taking a meristem (a piece of tissue free of the vascular tissue in which disease is carried), then heat-treating and culturing it, he could clone that plant and eradicate the disease. In the past 30 years, routine production of potatoes in some countries has included culturing potato meristems before growing out the seed.
Since establishing their partnership with NEU Seed, the team at Cibus has explored how to culture potatoes from single cells, instead of using nodal segments. (In the right conditions, it is possible to reproduce a whole plant, because that single cell contains the full genome.) Concurrently, they identified the single nucleotide changes (SNPs) that provide the potato plant’s genetic diversity. These SNPs will also provide traits that the growers from NEU Seed would like to develop. Since the folks at Cibus and NEU Seed already knew exactly what they wanted to target before they commenced researching, all Beetham and his team needed to do was find the particular gene in the particular germplasm for each trait.
It took about 12 months to accomplish those tasks. With their newfound understanding of how to clone the potato from the single cell efficiently, and with all the SNPs of the desired traits in the Russet Burbank variety identified, Beetham can alter the necessary gene within the cell. “We make a gene conversion using the smart breeding tool. It’s like using a spell checker to correct a word, but we’re changing that genomic code within the cell. Then, we culture it back to the potato and that’s our final product,” explains Beetham.
In the next couple of years, Beetham will apply RTDS within the potato cells, culture the cells with the altered DNA, and test the plants in the greenhouse and in the field. After initial material testing at Cibus’ greenhouses in San Diego, the members of NEU Seed and researchers at the U of Idaho will test the RTDS-altered seeds at small plots in Idaho. Presuming these trials are successful, members of the NEU Seed collaborative will multiply the material to make it available for the general market.
They anticipate release of the new Russet Burbank potato to the general market in 2014. Beetham believes farmers will appreciate the new traits created with RTDS because they are non-transgenic and don’t have any regulatory issues. Esplin and Beetham expect the results will benefit both conventional and organic potato growers.
Once this project is finished, Cibus and NEU Seed intend to research and develop enhanced traits for other varieties of potato. So far, it seems RTDS can create a number of interesting traits, from production and agronomic traits to quality traits. Beetham says that in developing the technology for Russet Burbank, he and his colleagues will be effectively creating an RTDS operating system for potatoes that can easily translate into other varieties.
The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.