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

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

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; 2^oR=secondary roots.

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

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

Shapes

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