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New directions in potato breeding

One of the knocks against commercial potatoes is their high glycemic index, a facet breeders are working to reduce.

Although it is not considered a “flashy” vegetable, the potato is about
to get a major makeover. Unlike a typical makeover though, this one is
more than skin deep.

Due to increased consumer interest in healthy eating and those with
boosted nutrient content, or “superfoods”, spuds with a lot more
pizzazz are about to take centre stage. “Definitely more varieties are
coming,” says Tom Hughes, president of leading potato distribution
company MacKay & Hughes in Toronto (www.earthfreshfoods.com).  
 
More than 160 cultivars of potatoes are presently sold in Canada, yet
70 percent of total seed acreage is devoted to only 10 of those, says
Dr. Benoit Bizimungu, an Agriculture and Agri-Food Canada (AAFC) potato
breeder based at the Lethbridge Research Centre in Alberta. “Apart from
some yellow-fleshed cultivars such as Yukon Gold, relatively few
pigmented-fleshed potatoes are on the market. Some heritage and
European cultivars are being grown but still on a small scale for
specialty markets.”

However, even though potatoes with brightly coloured flesh, deep
yellow, red, blue or purple, are not widely available, there are strong
indications they will be soon. Bizimungu says two purple-fleshed and a
number of yellow-fleshed selections from the AAFC potato breeding
program at Fredericton, New Brunswick, and Lethbridge are undergoing
industry evaluation.

As many growers know, AAFC creates about 350 new potato hybrid
combinations and grows about 120,000 new seedlings per year, and offers
the industry an opportunity to annually evaluate between 10 and 20
advanced selections of interest for evaluation and eventual
licensing. These selections have undergone at least six years of
rigorous field and laboratory testing. Bizimungu says that in addition
to this work, “New tools are being developed and evaluated to speed up
the determination of potato tuber composition and the selection of
clones high in compounds with antioxidant properties, including the
utilization of molecular markers and near infrared spectrometry.”

Antioxidants
Antioxidants are natural compounds associated with lower incidence of
chronic diseases such as cardiovascular disease, certain cancers and
eye diseases. Potatoes with coloured flesh have significantly higher
antioxidant content than white potatoes, with the highest amount found
in the red-, blue- and purple-fleshed varieties. “The colourful
potatoes are the fastest-growing product we have,” says Hughes.
“However at this point, that’s not necessarily because of the health
benefits, but because people are looking for something unique to put on
the plate.”

Dr. Michele Konschuh, a research scientist with Alberta Agriculture,
Food and Rural Development, has studied levels of the antioxidant
lutein in recent years, and found they are high enough in
yellow-fleshed varieties to support a claim of “contains lutein” on
packaging. Studies have indicated that lutein can help slow the onset
of age-related macular degeneration, a disease that strikes one in
three Canadians aged 55 and older. She also found that potatoes with
flesh of a deeper yellow may have greater lutein content, as may
smaller tubers or those that have experienced stress while growing. 
 
Of the varieties tested, including Agata, Cecile, Innovator, Island
Sunshine, Piccolo, Sante, Satina, Sinora, Victoria and Yukon Gold,
“Satina was most consistent in delivering a high level of lutein,”
Konschuh says. “Based on an average serving size estimate of 175 grams,
a helping of potatoes could contribute a significant portion of the
daily allowance of lutein.”

There is more good news. Cooking boosts lutein measurements in some
varieties, and, since the body absorbs lutein better with fat, adding
butter or margarine to these potatoes is guilt-free.

In terms of marketing potatoes on this basis, Konschuh says
“Consultants have told us levels of lutein were sufficient to
distinguish these potatoes, offering something significant enough to
consumers that they might be willing to pay a premium for it.”

Konschuh says if industry participation is strong, testing new
varieties for lutein content and developing agronomic information that
will help growers produce lutein-rich potatoes on an informed,
commercial basis may follow. “We have the seed money for the research
and we’re prepared to work with companies, but no one has taken the
bait yet,” she states.

Hughes adds “Right now there is a lot of confusion about what you can
put on the bag. We already have potatoes that are significantly higher
in antioxidant content than others, but we can’t put that on the label
yet.”

Glycemic index
In addition to having higher antioxidant content potatoes available
widely in the next few years, Canadians are likely to see low glycemic
potatoes as well. Today’s commercial potatoes possess some of the
highest glycemic indices of all food products, meaning that they
contain carbohydrates that are quickly digestible when cooked,
producing a blood glucose level spike shortly after eating. Many
consumers prefer complex carbohydrates that are digested more slowly
and contribute to better blood sugar stability.

Bizimungu says, “The glycemic index potential of potato is, to a large
extent, related to the availability of its starch for digestion and/or
absorption in the gastrointestinal tract. Breeding potatoes with a
lower glycemic index involves identifying selections that are high in
slowly digestible starches and dietary fibre.”

This year, Bizimungu and his colleagues have identified an initial
group of about 100 candidate varieties that will be subjected to
screening for slowly digestible starch. The selected ones will
eventually be tested for their effect on human blood sugar levels.

Bizimungu adds, “A significant focus of the study is also the
identification of a genetic indicator and new tools that could be used
to identify and speed up the development of future potatoes with a
lower glycemic index.”