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

 ‘Japanese’ sweet potatoes

Fig. 1. ‘Japanese’ sweet potatoes in a commercial field near Faison NC harvested October 16, 2003.

 External and internal appearance of ‘Japanese.’

Fig. 2. External and internal appearance of ‘Japanese.’

Table 1a. Clinton Specialty Yield Trial.   Total and marketable yield, percentage of total yield by size distribution and percent dry matters of sweet potato clones harvested 119 days after planting at the NCSU/NCDA HCRS, Clinton, Sampson Co., NC – 2004. Clones that had purple flesh color are suffixed with (PSP).
Size Distribution by Class1
  Total Yield Marketable Yield (% of total yield) % Dry
CLONE bu/A bu/A % Beau % Japanese No.1’s Canners Jumbo’s Culls Matter
B94-14 G2 560 541 . 123 57 36 4 3 24
NCBON99-477 563 431 81 99 50 15 12 23 26
NC415 (PSP) 547 497 93 114 57 15 17 10 33
NC415 (PSP) G1 503 427 80 98 58 16 11 15 33
Grand Asia 427 400 75 92 41 51 2 7 34
Hannah 356 286 54 66 46 33 1 19 29
Japanese G3 467 442 82 . 59 27 8 6 33
Kyukie 97 414 406 76 93 63 28 6 2 35
L258 588 346 65 80 35 8 16 41 31
O’Henry G1 560 525 98 120 56 31 7 6 26
Okinawa G1 (PSP) 396 310 57 70 40 36 2 22 34
Picadito G1 646 596 113 138 50 9 34 8 31
NCPUR01-192 561 473 88 108 52 14 18 16 35
White Delite G1 622 579 111 136 54 39 0 7 25
Mean 515 447 82 103 51 26 10 13 30.7
CV 14 16 18 17 21 33 63 54
LSD 100 102 21 25 15 12 9 10

1US#1’s – Roots 2″ to 3 1/2″ diameter, length of 3″ to 9″, must be well shaped and free of defects

Canners – Roots 1″ to 2″ diameter, 2″ to 7″ in length.

Jumbos – Roots that exceed the diameter, length and weight requirements of the above two grades, but are of marketable quality.

Percent US#1’s – Calculated by dividing the weight of US#1’s by the total marketable weight (Culls not included).

Culls – Roots must be 1″ or larger in diameter and so misshapen or unattractive that they could not fit as marketable roots in any of the above three grades.

Table 1b. Clinton Specialty Yield Trial. Storage root attributes1 of sweet potato clones harvested 119 days after planting at the NCSU/NCDA HCRS, Clinton, Sampson Co., NC – 2004.
CLONE MAT DM L/D SKC SKT FL EYE LEN SH SHV APP Comments2
B94-14 G2 EM 24 2.5 rs ms 2.75 8 7 3,6 6 6
NCBON99-477 M 26 1.5 pi sm 1.5 7 7 2,3 6 5 ^CR, RC?, skins easily
NC415 ML 33 2.5 pur ms Pur 7 7 3,6,2 6 6
NC415  G1 ML 33 2.5 pur ms Pur 7 7 3,2 5 5
Grand Asia L 34 4.5 pur sm 1.5 6 7 3,4 7 5 too L
Hannah L 29 1.5 tan ms 2 8 8 3,2 5 5 ~CR
Japanese G3 M 33 3 pur ms 1.5 6 7 3,5 5 6 L, better than GA for shape
Kyukie 97 ML 35 2.5 pi sm 1.5 6 6 3,6 6 4 low yld, field survival?
L258 ML 31 2 pi sm 1.5 5 7 3,6,5 6 6 ^CR, EY, g potential
O’Henry G1 M 26 3 w sm 2 8 6 3,6 6 6
Okinawa G1 L 34 5 cr sm Pur 6 8 4,7 4 3 ^CR, L
Picadito G1 L 31 3.5 pur ms 1 6 6 3,2 4 4 sets roots far from hill
NCPUR01-192 L 35 1.5 pur ms Pur 7 7 3,5 5 4 LG, 80% purple
White Delite G1 ML 25 1.5 pi sm 2 7 8 3,2 6 5 ~CR

1Storage root attributes: Maturity E-early, M-midseason, L-late; DM=%dry matter; L/D=Length/Diameter; skin color; skin texture; flesh

color (1=white, 2=yellow, 3=orange); eyes(0-9); lenticels(0-9); shape (see diagram); shape variability(0-9); overall appearance(0-9).

Rating scale: 0= very poor to 9=excellent.

2Comment codes: AT=tough attachment; B=bumpy; BSR=bacterial soft rot; CLSH=culls for shape; CR=cracking; CS=circular spot;

CV=skin color variation end to end;  FB=fleabeetle; HC=horizontal constrictions;  LG=longitudinal grooves; LR=Lateral rings; LT=latex;

MN=Mottle Necrosis; MSH=misshapen; PI=pimples;  R=rodent;  RC=russet crack; RE=rows of eyes; RKN=root-knot nematodes;

SC=scurf; SD=skin discoloration; SF=surface fusarium; SG=string roots; SPR=sprouts; SR=soft rot;  SSR=streptomyces soil rot;

STR=Striations; T=tails; VN=viens; WB=whitefringed beetle; WG=white grub; WW=wireworm;  YCR=yellow cortical ring

(Rating scale: 0 = very severe to 9 = absent)

Table 2a. Kinston Specialty Yield Trial. Total and marketable yield, percentage of total yield by size distribution and percent dry matters of sweet potato clones harvested 144 days after planting at the Cunningham Research Station, Kinston, Lenoir Co., NC – 2004. Clones that had purple flesh color are suffixed with (PSP).
Size Distribution by Class1
  Total Yield Marketable Yield (% of total yield) % Dry
CLONE bu/A bu/A % Beau %Japanese No.1’s Canners Jumbo’s Culls Matter
NCBON02-442 1081 1061 93 163 68 9 22 2 19
B94-14 G2 1162 1155 . 177 66 17 17 1 18
NCBON99-477 825 779 69 117 64 23 8 6 21
Carolina Ruby 923 861 75 131 64 24 6 6 20
NC415 (PSP) 666 588 52 89 61 11 17 11 28
Grand Asia 705 623 54 94 51 33 4 12 29
Hannah 455 399 35 60 39 47 2 13 27
Japanese G3 745 670 59 . 60 27 4 10 30
Kyukie 97 696 587 51 91 33 44 7 16 32
L258 1061 687 60 103 44 9 13 35 26
O’Henry G1 674 646 56 101 66 23 7 4 19
Okinawa G1 (PSP) 374 351 31 55 31 65 0 4 28
Picadito G1 996 977 85 153 64 12 22 2 30
NCPUR01-192 802 779 69 118 58 20 19 3 27
White Delite G1 884 865 75 134 40 57 1 2 22
Mean 803 735 61 113 54 28 10 8 25
CV 15 17 17 19 18 30 80 100
LSD 173 176 15 31 14 12 11 12

1US#1’s – Roots 2″ to 3 1/2″ diameter, length of 3″ to 9″, must be well shaped and free of defects

Canners – Roots 1″ to 2″ diameter, 2″ to 7″ in length.

Jumbos – Roots that exceed the diameter, length and weight requirements of the above two grades, but are of marketable quality.

Percent US#1’s – Calculated by dividing the weight of US#1’s by the total marketable weight (Culls not included).

Culls – Roots must be 1″ or larger in diameter and so misshapen or unattractive that they could not fit as marketable roots in any of the above three grades.

Table 2b. Kinston Specialty Yield Trial. Storage root attributes1 of sweet potato clones harvested 144 days after planting at the

NCSU/NCDA HCRS, Clinton, Sampson Co., NC – 2004.

CLONE MAT DM L/D SKC SKT FL EYE LEN SH SHV APP Comments2
NCBON02-442 E 19 2.5 pur ms 2 5 7 3 6 6.3 Early, few roots-large size
B94-14 G2 M 18 2.5 rs sm 3 8 8 3 7 6.8 good
NCBON99-477 M 21 2 pi sm 1.5 8 8 3 6 5.8 T
Carolina Ruby M 20 2.5 ted ms 3 7 6 3 6 6.0 T, culls -CR
NC415 M 28 2.5 dk pur m flk pur 7 7 3,5 5 4.0 T, AT, ~GR
Grand Asia M 29 3 pur s flk 1.5 6 7 3,6 5 4.3 CR, mixed sh
Hannah M 27 2.5 yel ms 2 7 7 3 5 4.8 long attachment, mixed sh
Japanese G3 M 30 3 pur s flk 1.5 6 6 3,7 5 4.5 CR, RC, ^ irr shapes
Kyukie 97 ML 32 4 pur ms 1.5 7 8 4 7 4.7 ^L, CR
L258 ME 26 3.5 pur s flk 1.25 6 7 3,6 6 5.3 CR, a bit long
O’Henry G1 M 19 2.5 cr sm 2 8 8 3 5 4.8 mixed shapes
Okinawa G1 L 28 4 w ms pur 6 73,7 3,7 3 3.0 L, IRR
Picadito G1 ME 30 3 pur m flk 1 8 7 3 4 4.7 VN, AT, deep set, few roots
NCPUR01-192 ME 27 2.5 dk pur m flk 50% pur 7 7 3,6 6 5.5 AT, GR
White Delite G1 L 22 2.5 pi sm 1.75 7 8 3,6 6 6.0 Late, ^^roots

1Storage root attributes: Maturity E-early, M-midseason, L-late; DM=%dry matter; L/D=Length/Diameter; skin color; skin texture; flesh

color(1=white, 2=yellow, 3=orange); eyes(0-9); lenticels(0-9); shape (see diagram); shape variability(0-9); overall appearance(0-9).

Rating scale: 0= very poor to 9=excellent.

2Comment codes: AT=tough attachment; B=bumpy; BSR=bacterial soft rot; CLSH=culls for shape; CR=cracking; CS=circular spot;

CV=skin color variation end to end;  FB=fleabeetle; HC=horizontal constrictions;  LG=longitudinal grooves; LR=Lateral rings; LT=latex;

MN=Mottle Necrosis; MSH=misshapen; PI=pimples;  R=rodent;  RC=russet crack; RE=rows of eyes; RKN=root-knot nematodes;

SC=scurf; SD=skin discoloration; SF=surface fusarium; SG=string roots; SPR=sprouts; SR=soft rot;  SSR=streptomyces soil rot;

STR=Striations; T=tails; VN=viens; WB=whitefringed beetle; WG=white grub; WW=wireworm;  YCR=yellow cortical ring

(Rating scale: 0 = very severe to 9 = absent)

 

 

Keys to Tables

 

Storage root data: MAT=maturity E=early, M=mid and L=Late; DM=percentage dry matter; L/D=length/diameter ratio; SKC=skin color clr=clear cu=copper, lt=light, or=orange, pi=pink, pu=purple, rd=red, rs=rose, tn=tan wh=white; SKT= skin texture, m fl= moderate flakiness of skin, lt fl= light flakiness to skin, ms=moderately smooth, sm=smooth; FL=flesh  color (0-5 scale where 0=pure white, 1= cream, 2=yellow, 3= medium orange, 4=deep orange, 5= very deep orange; EYE=eyes(0-9); LEN= lenticels (0-9); SH=Shape (see diagram); SHV=shape variability(0-9); APP=overall appearance (0-9). All 0-9 scales go from low or poor to high or good.

 

Comment codes: AT=tough attachment; B=bumpy shapes; BR=breeding only; BSR=bacterial soft rot; CR=cracking; CRK= crooked shapes; CS=circular spot; CV=skin color variation end to end; D=drop; EY=deep eyes; FB=fleabeetle damage; HC=horizontal constrictions; ID=unspecified insect damage; IRR=irregular; JL=jumbo’s for length; L=long; LE=lenticels; LG=longitudinal grooves; LR=Lateral rings; LT=latex; MSH=misshapen roots; NS=nice shapes; OV=ovate or pear shapes; PI=pimples (0-9); PN=pencil roots; PP=pulled plants; R=rodent; RC=russet crack; RG=restaurant grade; RH=root hais; RKN=root-knot nematodes; RSK=rough skin; RT=rot; SD=skin discoloration; SH=sheen; SG=string roots; SK=skinning; SO=souring; SPR=sprouts; SR=soft rot; SS=stays short; SSR=streptomyces soil rot; STR=Striations; T=tails; TP=tapered roots VN=veins; SC=scurf; SF=surface Fusarium; WB=whitefringed beetle; WG=white grub; WW=wireworm; YCR=yellow cortical ring; YLD=yield; 2oR=secondary roots.

= lots, ~ = moderate, ¯ = little or poor

 

(Rating scale: 0 = very severe to 9 = absent)

 

 

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