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Characterisation of orange-fleshed
sweetpotato varieties in South Africa:
agronomic traits, consumer
acceptability and nutrient content
S.M. Laurie
Agricultural Research Council - Roodeplaat Vegetable
and Ornamental Plant Institute
Sweetpotato Breeders Meeting,
27 June 2011, Maputo
Background
• Formal market: 50 000 – 60 000 Mt/annum +
informal market ± same; mostly CFSP
• Recent large increase OFSP for frozen
vegetable industry: Beauregard 425 ha, Purple
Sunset (ARC) 225 ha
• VAD: 64% of 1-9 year olds, 27% women at child-
bearing age
• Food security: 30% households at risk
Rationale
• Require improved OFSP to expand production
• Breeding aimed at good yield, good β-carotene
content, dry mass %.
• USA imports, ARC lines/variety 2006-8
• Aim:
– to characterize OFSP …
1) agronomic performance
2) consumer acceptability, sensory
traits
3) mineral and β-carotene content
in order to recommend varieties for addressing
VAD and for use in new markets.
Methodology
1. Varieties
– 9 OFSP varieties/lines: Khano, Serolane and Impilo; lines
1999-1-7 and 2001-5-2; Excel, W-119 and Resisto from USA,
Beauregard (USA variety) commercial use;
– 3 CFSP: Blesbok (Com), Ndou & Monate (dry, sweet)
2. Multi-location trial sites
– Two seasons per site at four sites during 2005/6 to 2008/9.
– EC1 & EC2: Communal garden (Eastern Cape); (temperate)
– E1 & E2: Elsenburg Agric. College (Western Cape); (dry, hot)
– OS1 &OS2: Owen Sithole College (KwaZulu-Natal);(sub-tropical)
– R1 & R2: Research center Roodeplaat (Gauteng); (temperate)
– 3 reps x 30 plants
– Supplementary irrigation & fertilization
– Growing period 4.5 – 5.5 months
3. Sensory evaluation
- Cooked samples evaluated by trained panel
for appearance (yellow-green color, orange
color, dark edges, discoloration), flavor
(sweetness, sweetpotato flavor, pumpkin
flavor) and texture (firmness, graininess,
wateriness)
- Instrumental color and texture
- Content of free sugars (glucose, fructose,
sucrose, maltose) and starch.
4. Consumer acceptability
- Tested by a panel comprising 168 primary
school children and 48 adults in
Dassenhoek, KwaZulu-Natal, using a
Balanced Incomplete Block Design.
5. Nutrient content
- Randomly collected 8 medium roots
- From 4 geographical areas (ARC-
Roodeplaat, Empangeni, Giyani and
Hazyview).
- Send intact to analytical labs
- Content of 6 minerals (by OES) & trans-β-
carotene (by HPLC)
6. Data processing & analysis
- ANOVA
- GXE: SREG model of GGE Biplot (G main
effect plus G x E interaction)
- Correlation analysis between sensory &
consumer data, PLS to indicate most
distinctive attributes, group varieties
- Elston Selection Index
Results
Appearance of sweetpotato cultivars
Impilo
GGE Biplot: Total yield
Unmarketable yield classes
• XXL (early maturing): Beauregard
• XXS: Serolane, Impilo, 1999-1-7 and Khano.
• Root cracks: Excel, Impilo and Khano.
• Insect damage: Beauregard, Ndou and Impilo
• Mechanical damage (long roots) W-119
• Long curved (slender): 1999-1-7
• Sprouting to some extent in Impilo
• Mean root weight:
– Beauregard and W-119 (high), an indication of early maturity.
– Serolane, Excel, Impilo and 2001-5-2 (intermediate).
– 1999-1-7, Khano and Resisto (small).
GGE Biplot: Marketable yield
• Ideal varieties have high PC1 scores (high yield) and
small absolute PC2 scores (high stability), e.g. Impilo
and Beauregard).
• Stable, wide adaption, high yielding:
Beauregard, Impilo
• Unstable, specific adaption, high yielding :
2001-5-2, 1999-1-7
– responsive has the specific advantage that it may be able to
respond to changes in environment
• Stable, wide adaption, average to below average yields:
Khano
• Unstable, specific adaption, low yielding:
Excel, Serolane
• Stable, wide adaption, low yielding:
Resisto, W-119
Consumer acceptability of color and taste
Variety Mean color score 2 Variety Mean taste score 2
Monate 1 3.56 (1.19) Monate 1 3.82 (1.19) a
Excel 3.46 (1.32) Impilo 3.79 (1.38) a
Beauregard 3.43 (1.35) 2001-5-2 3.72 (1.25) ab
Blesbok 1 3.43 (1.20) Serolane 3.71 (1.21) ab
1999-1-7 3.39 (1.34) Excel 3.69 (1.36) ab
Serolane 3.36 (1.32) Resisto 3.68 (1.31) ab
2001-5-2 3.33 (1.35) W-119 3.67 (1.29) ab
Impilo 3.31 (1.25) Ndou 1 3.65 (1.21) ab
Resisto 3.26 (1.41) Blesbok 1 3.40 (1.30) abc
Ndou 1 3.17 (1.42) 1999-1-7 3.33 (1.34) bc
W-119 3.04 (1.33) Khano 3.14 (1.44) c
Khano 3.00 (1.38) Beauregard 3.11 (1.42) c
Mean 3.31 3.56
P-value (variety) 0.2932 0.0032
LSD 0.43 0.43
CV% 39.6 36.8
Means for varieties in a column followed by the same letter are not significantly different at P ≤ 0.05
1 Cream-fleshed varieties
2 Scale for scores: 1=very bad; 2=bad; 3=indifferent; 4=nice; 5=very nice
Correlation analysis
• Orange-fleshed varieties were lower in sweet potato-like
flavor and higher in pumpkin-like flavor.
• Orange-fleshed varieties were generally higher in
graininess and pumpkin-like flavor.
• And had higher sucrose content
• Consumer panel taste scores associated most with sweet
flavor, dry matter and maltose content; consumer panel
color scores negative association with discoloration.
• Adult consumer taste score negatively correlated to
wateriness
• Determination of dry matter and starch content, and
sucrose equivalents in cooked roots can possibly be used
in intermediate selection phases in breeding as indication
of acceptable taste.
0.5
Partial Least
Squares 0.4
Regression Khano Discolour
analysis 0.3 Gumminess
Instronforce
Color a* Color b*
0.2 Color L* Edges
Beauregard
Orange
1999_1_7 Sucrose
Ndou Serolane
0.1
PLS component 2
Pumpkin-like
Graininess W_119
Wateriness Starch
Firmness
0
Maltose
Dry matter %
Free sugar:Starch
-0.1 Sweetpotato-like
Blesbok Impilo Excel
Yellow-green
Resisto
Glucose 2001_5_2
-0.2
Fructose Monate Sweet
CPColor
-0.3
-0.4
CPTaste
-0.5
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
PLS component 1
Group and PLS Major attributes
variety ranking
Group 1
Blesbok -5.2 Watery texture, yellow-green color, sweet potato-like flavor, high fructose and
sucrose content and contrasting dry matter %, dark edges and discoloration
Group 2
Beauregard -2.6 Watery texture and low dry matter %, not sweet, low maltose content
Khano -0.4 Low dry matter, not sweet, high in discoloration, dark edges, instronforce,
gumminess, color a*, orange color and sucrose content
1999-1-7 -0.1 Low dry matter %, low firmness, low fructose content, medium sweet
Ndou 0.3 Sweet potato-like flavor, yellow-green color, high starch %, high color L* , low
graininess
Group 3
Impilo -0.7 Sweet, medium dry matter %, high fructose and glucose content, slight yellow-
green color, high discoloration, high pumpkin-like flavor, low starch %
Monate -0.5 Sweet, medium dry matter %, sweet potato-like flavor, yellow-green color, low
instronforce, low discoloration, low graininess
2001-5-2 0.9 Sweet, medium dry matter % and pumpkin-like flavor, high fructose and
glucose content, color a*, orange color; low starch %, dark edges, discoloration
and starch %
Excel 1.5 Low wateriness, medium dry matter %, medium sweet, high pumpkin-like flavor,
high dark edges, high graininess
Resisto 2.5 Low wateriness, high dry matter %, medium sweet and pumpkin-like flavor, low
glucose content, color a* , orange color
Group 4
W-119 1.5 High starch %, high instronforce and gumminess, high graininess, high
pumpkin-like flavor, high firmness, orange color, high dry matter %
Serolane 2.9 High starch %, high instronforce and gumminess, high color L* and color b*,
low fructose and sucrose content, high maltose content, slight sweet potato-
like flavor
Nutrient content: means of 4 sites (raw root)
Variety trans-β- Vitamin Dry Ca Mg P K Fe Zn
carotene A value mass
µg /100g µg trans-β-carotene content of 9 OFSP
- Overall meanRAE % mg/100g mg/100g mg/100g mg/100g mg/100g mg/100g
Resisto varieties was 9706 µg/100 g raw root 45
16456 1371 27.3 63 30 (varying between 0.60
272 0.91
and 1170 22.4
Khano 5091 14036 16456 µg/100 55 g). 37 46 314 0.81 0.64
- Varieties with β-carotene content above the 234
2001-5-2 11800 983 23.9 53 26 33
level 0.67
target 0.80
W-119 10464 872 28.7 63 31 42 263 1.26 0.60
for use in the crop-based programs (5500 µg/100 g)
Beauregard 9646 804 19.8 49 21 30 249 0.76 0.69
1999-1-7 were Resisto, Khano, 2001-5-2, W-119, Beauregard and 0.56
9558 797 25.1 48 29 43 297 1.15
Excel 1999-1-7. 433 26.7
5200 52 29 43 291 0.81 0.64
Serolane 5106 426 30.5
- Impilo, Excel, Serolane (5109 to 522051
54 33 334 0.99
µg/100 g trans-β- 0.62
Impilo 5091 424 23.1 51 27 45 286 1.17 0.60
Ndou 1
carotene) are useful to populations with mixed dietary 0.60
134 11 27.0 37 20 42 309 0.73
Monate 1 sources of vitamin A.
31 3 24.9 34 20 38 291 0.84 0.53
- Overall mean1mineral content in 9 varieties was as
Blesbok 1 14 18.7 39 15 28 191 0.78 0.51
follows: 54 mg/100 g calcium, 29 mg/100 g magnesium, 0.60
Overall mean 7294 24.8 50 26 40 278 0.93
40 9706
Mean OFSP mg/100 g phosphorous, 282 mg/100 g potassium,
25.3 54 29 42 282 0.96 0.62
Mean CFSP 60 23.5
0.96 mg/100 g iron, and 37 0.62 mg/100 36 zinc.
18
g 264 0.78 0.55
LSD 2640 1.49 12.9 5 3.1 41.4 ns ns
CV% 18.7 7.2 18.1 13.1 9.1 10.4 31.1 15.1
• OFSP mostly superior in mineral content
• In context of human nutrition in South Africa, all the
orange-fleshed varieties, when boiling a raw portion of
100 g, have a potential contribution of ≥100% of the
recommended intake for vitamin A, e.g. for 4 to 8 year
old children, and 21% to magnesium, 12% to zinc and
9% to iron requirements.
Index selection: Elston
Testing in MET Consumer panel Nutrient analysis Sensory attributes Elston
Taste Vine Marketable Total Mean Mean Beta- Dry Maltose Sweet Wateriness 5 Discolo index
Variety MET vigor 2 Yield Yield color taste carotene matter % Flavor 4 ration 5 rank
score 1 t/ha t/ha score 3 score 3 µg/g raw content %
root
2.51 3.83 35.6 b 55.0 a (2) 3.56 3.82 a 0.31 e 24.9 cde 8.05 52.2 ab 18.5 a 7.4 cd 168525080
Monate 6 (3) (1) (2) (1) (1) (11) (7) (3) (2) (9) (3) 1
2.84 3.32 31.1 c 44.8 bc (4) 3.31 3.79 a 50.91d 23.1 de 7.65 53.1 a 19.8 a 19.6 a 19424897
Impilo (9) (4) (4) (8) (2) (8) (9) (4) (1) (11) (12) 2
2.81 3.56 35.0 b 46.2 b (3) 3.17 3.65 ab 1.34 e 27 bc 10.11 50.4 abc 18.4 a 11.5 17976624
Ndou 6 (8) (3) (3) (10) (8) (3) (4) (2) (3) (8) bcd 3
(9)
2.49 3.13 27.0 de 37.2 e (8) 3.33 3.72 ab 118.00 bc 23.9 de 7.26 47.1 abc 17.6 ab 6.5 cd 14993694
2001-5-2 (2) (8) (7) (7) (3) (10) (8) (6) (5) (6) (2) 4
2.04 3.22 19.6 f 31.0 f 3.46 3.69 ab 52.00 d 26.7 bc 7.18 42.9 bcde 10.1 c 10.8 7502866
Excel (1) (7) (11) (10) (2) (5) (7) (5) (7) (7) (4) bcd 5
(7)
3.07 (12) 2.69 27.9 cd 39.1 de (6) 3.39 3.33 bc 95.58 c 25.1 cd 6.5 49.1 abc 11.8 bc 11.1 5006303
1999-1-7 (12) (6) (5) (10) (6) (6) (9) (4) (5) bcd 6
(8)
2.57 3.03 20.0 f 36.5 e (9) 3.36 3.71 ab 51.06 d 30.5 a 11.53 42.3 bcde 7.7 c 13.8 4143986
Serolane (4) (9) (10) (6) (4) (9) (1) (1) (8) (2) abc 7
(10)
2.70 3.29 19.5 f 27.0 g (1) 3.04 3.67 ab 104.64 c 28.7 ab 6.72 40.7 cde 7.2 c 10.5 179843
W-119 (6) (5) (12) (11) (7) (4) (2) (8) (9) (1) bcd 8
(6)
2.88 (10) 3.26 40.2 a 56.6 a (1) 3.43 3.40 0.14 e 18.7 f 5.16 34.4 ef 23.3 a 4.9 d 4463
Blesbok (6) (1) (4) abc (9) (12) (12) (11) (11) (12) (1) 9
6
3.35 (11) 3.64 24.5 e 37.7 e (7) 3.00 3.14 c 140.36 22.4 e 6.43 36.3 def 18.2 a 16.7 ab 0
Khano (2) (8) (12) (11) ab (10) (10) (10) (7) (11) 10
(2)
2.81 2.89 30.3 cd 42.4 cd (5) 3.43 3.11 d 96.46 c 19.8 f 5.14 30.0 f 18.9 a 8.2 cd -3458
Beaureg (7) (10) (5) (3) (12) (5) (11) (12) (12) (10) (4) 11
ard
2.69 2.84 20.7 f 27.0 g (12) 3.26 3.68 ab 164.56 a 27.3 bc 7.3 44.8 abcd 9.6 c 8.9 cd -2337314
Resisto (5) (11) (9) (9) (6) (1) (3) (5) (6) (3) (5) 12
2.78 3.22 27.6 40.05 3.31 3.56 72.94 24.8 7.42 43.6 12.9 10.8
Mean
Roodeplaat 2 ha
Discussion
• Improvements in yield coupled with
good taste and dry matter content.
• Considerable root yield advantage over
the USA imports Resisto, Excel and W- Bophelo
119 initially used in crop-based Venda 1 ha
programs.
• Impilo and 2001-5-2 were found to be
promising (all-round performance).
• Tolerance - virus
– drought tolerance: both intermediate
eManguzi 2 ha
– stem blight: Impilo T; 2001-5-2 Interm.
– weevil and other insects:
– vine persistence: Impilo medium thick
– vine multiplication rate: 2001-5-2 higher
Acknowledgements
- The ARC for research funding
- ARC - Biometry Unit: statistical analysis
- Dr Mieke Faber (MRC) and Dr Annalien Dalton for
collaboration in the consumer analysis
- Ms Nina Muller and Ms Erika Moelich, University of
Stellenbosch for conducting sensory profiling
- Dr Paul van Jaarsveld, MRC, for beta-carotene analysis.
- ARC-Institute for Soil Climate & Water for mineral analysis
- Department of Agriculture & communities for their role in
execution of the agronomy trials
- ARC technicians assisting with trials at off-station locations:
Mr Musa Mtileni, Ms Sharon Mulandana, Mr Sidwell Tjale.
- Prof Maryke Labuschagne, Department of Plant Sciences,
University of Free State.
Development of a high throughput
drought screening method
• Year 1:
– Rainout shelters – 4cv x 3 regimes x 3
Leaf samples 212
reps (24 plants/plot) Root samples 106
– Small shelters: 35 cv x 2 regimes x 2 reps
(5 plants/plot)
• Year 2:
– Rainout shelters – 8cv x 2 regimes x
3 reps (24 plants/plot)
– Field trials: 35 cv x 2 localities x 2 regimes
x 3 reps (12 plants/plot)
Leaf samples 464
Root samples 282
LUTZVILLE RIETRIVIER
C12:C13 partitioning
Absicic acid
Anti-oxidants – peroxidase,
glutatione reductase
GGE biplot: advantages of use
• Offers breeders a complete, visual evaluation
• Kang’s yield stability statistic, YSi, (Kang, 1993; Yan, 2001; Yan
and Kang, 2003).
• According to Yan et al. (2001) biplot readily visualizes:
1) the similarities and differences among environments in their
discrimination of varieties;
2) the similarities and differences among varieties in their
response to environments; and
3) the magnitude and type of interaction between varieties and
environments.
• The GGE biplot has been used in yam, another vegetative-
propagated crop, by Otto and Asiedu (2009)
• It allows more functions than AMMI (Ding et al., 2007).
• E.g. yield relative to environment maximum (YREM), relationships among
environments, discriminativeness & representativeness of test
environments, ideal test environments, similarity of genotypes, mean
performance and stability of the genotypes, and which-won-where
analysis. Each of which has its own type of biplot.
