Identifying
Specialty-type Sweet Potato Cultivars
Adapted to NC Growing Conditions
PROJECT LEADER(S): Kenneth Pecota, Bill Jester and
Craig Yencho
LOCATION: Cunningham Research Station, Kinston
and the Horticultural Crops Research Station, Clinton
IMPACT
This project will contribute to the diversification of the
farming industry in Eastern NC. As more and more farmers transition out of
tobacco they are looking to produce other high value crops. NC is already the largest producer of sweet
potatoes in the US
and growers can make a reasonable profit from this vegetable crop. Many growers are already familiar with
cultivating the crop as it is often produced in rotation with tobacco. Like tobacco, sweet potatoes are part of the
fabric of life in many rural eastern NC communities so it is not too difficult
to get growers to try new specialty-types.
Large to medium-sized established growers can tap into well-established
marketing outlets to market these new specialty-type varieties, while smaller and
new growers interested in producing specialty-type sweet potatoes, can work to
establish community-based niche markets.
Several growers are already
producing ‘Japanese’ and ‘Picadito’ specialty-varieties with acreage estimated
to be over 300 acres. Indeed, one grower
is currently producing ‘Japanese’ for use as chipping stock in addition to the
fresh market. We believe that the
potential for these markets has not been reached and that given suitable
cultivars, NC could also be a leader in the production of specialty-type sweet
potatoes.
INTRODUCTION
The Asian and Hispanic segments of the US
population are the fastest growing sectors of the US population. Per capita, they consume larger quantities of
sweet potato compared to more traditional consumers. However, Asian and Hispanic consumers prefer
different types of sweet potatoes than what are typically grown in the US. These specialty-type sweet potatoes are often
called “boniato- or Japanese-types.”.
Sweet potatoes suitable for Asian and Hispanic markets typically have a
high dry matter content and are white- to cream-fleshed, and they are more
similar to a potato in texture and taste than the moist very sweet,
orange-fleshed sweet potatoes typically grown in NC. Externally, they differ from the
white-fleshed sweet potatoes grown here in that they generally have purple to
red skin and have a milder flavor. To
further complicate things, the Asian and Hispanic varieties look similar but
differ in sweetness. Typically the Asian markets prefer sweet potatoes that are
slightly sweet when cooked, while the Hispanic varieties are usually non-sweet.
Currently there are no available boniato- type
or Japanese-type varieties that are well adapted to NC's climate. Part of the reason for this is that most of
the growing regions for this type of sweet potato are semi-tropical or
tropical. Also, most of these varieties
are typically very long season, not resistant to soil rot, and they do not
store well.
This
project will contribute to the diversification of the sweet potato industry in Eastern NC. NC is already the largest producer of sweet
potatoes in the US. Large to medium-sized established growers can
tap into well-established marketing outlets to market these new specialty-type
varieties, while smaller and new growers interested in producing these can work
to establish community-based niche markets.
But, simply introducing new adapted specialty-type cultivars is not
enough to ensure penetration into the Asian and Hispanic markets. It will take a coordinated effort in
identifying, growing, storing and marketing these unique materials to insure
that the right product, with high quality is delivered to these markets. The SCP is an ideal means in which to introduce
specialty-type sweet potatoes to NC’s growers.
METHODS
During
2004, we evaluated 14 clones at the HCRS and 15 clones at the CRS in our
specialty-type trials (Tables 1 and 2).
Beauregard and Japanese were used as check varieties in each trial. Many of the clones, are lines that we have
developed in our breeding program. Or
they represent clones that we have collected from various sources and submitted
to the NCSU Micro propagation Unit (MPU) for virus-indexing and field
evaluation prior to evaluation in the field to prevent introduction of new
viruses to the NC sweet potato production system. Both tests went very well this year. As typically experienced, yields at the CRS
station were significantly higher due to the quality of the soils at that site. Each test was hand graded in the field for
yield by No.1, canner, jumbo and cull classes and evaluated for horticultural
characteristics including maturity, shape, shape variability, skin color, flesh
color, eyes, lenticels, diseases present, length/diameter ratio and overall
appearance. All the clones were also
entered into our disease screenings for root knot nematodes, Fusarium wilt and
pox.
RESULTS
Tables
1 and 2 summarize the results of the specialty-crop trials conducted during
2004. We have bred or obtained a good
collection of white to cream-fleshed sweet potatoes of varying dry matter
content (18-30+%) and sweetness. Our collection
of materials possesses white, purple, red and pink skin colors. As part of our purple-fleshed breeding
program (see our other GLF report) we have also either obtained or bred light
to dark purple-fleshed sweet potatoes, which also have utility as a
specialty-type especially for health conscience consumers. None of these new clones have been tested
enough to replace the clone ‘Japanese’ which was identified by this project
earlier as the best cultivar currently available for NC growers. However, we are encouraged by the performance
of Grand Asia, NCBON02-442 and L258 (see Tables 1 and 2).
The
most popular Boniato-type sweet potato is ‘Japanese.’ Several producers are currently growing it,
and we estimate that over 300 acres were planted during 2004. However, one of the weaknesses of ‘Japanese’ is its susceptibility to russet
crack. It declines rapidly for yield and
appearance making the use of clean stock very important. One of our goals for this year was to release
a virus-indexed ‘Grand Asia,’ which is similar to ‘Japanese’ but have not seen
russet crack expressed in this clone. We
evaluated a virus-indexed ‘Grand Asia’ clone in both our trials this year. Its yield and dry matter content are very
similar to that of the ‘Japanese,’ and its overall appearance is very similar,
though ‘Japanese’ is generally more attractive and slightly shorter in
length. ‘Grand Asia’
is now available in the MPU and several growers will be trying this clone
during the 2005 season on-farm.
‘Picadito’,
the main cultivar used for the Hispanic market, performed surprisingly well in
both locations during 2004. It actually
out-yielded ‘Beauregard’ in the CRS trial, but its appearance was 4.7 compared
to 6.8 (1= poor ; 9 = excellent). We do
not recommend this clone for NC growers because of its poor adaptability and
appearance, though we realize that appearance per se is not the most important
factor in the marketing of this variety.
CONCLUSION
The best
available sweet potato cultivar suitable for Asian markets in NC is
‘Japanese.’ ‘Grand Asia’
may also have utility but it will have to prove itself in large-scale trials,
which will be initiated during 2005.
‘Picadito’ is the most widely grown cultivar for the Hispanic markets,
but it has limited adaptation to NC. All
three clones are susceptible to root knot nematodes and soil rot or pox
disease. Picadito is also susceptible to
Fusarium, while ‘Japanese’ is susceptible
to russet crack. Because of the disease
susceptibilities each variety should be grown in a sound rotation program and
using clean planting stock. Virus-indexed micro propagated plants are available
from the NC State Micro propagation unit.
During 2005, we plan to continue further evaluations of specialty-type
sweet potatoes as we have several new preliminary lines that show promise.
TABLES AND PHOTOS
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Fig.
1. ‘Japanese’ sweet potatoes in a commercial field near Faison NC
harvested October 16, 2003.
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Fig.
2. External and internal appearance of
‘Japanese.’
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