Phenotypic Variability and Evaluation of Yam (Dioscorea spp.) Landraces from Southwest Ethiopia by Multivariate Analysis

 

Tewodros Mulualem1,2, Firew Mekbib2, Shimelis Hussein3, Endale Gebre4

1Jimma Agricultural Research Center, P.O. Box 192, Jimma, Ethiopia

2Haramaya University, School of Plant Sciences, P.O. Box 138, Dire Dawa, Ethiopia

3African Centre for Crop Improvement, School of Agriculture, Earth and Environmental Sciences,

University of Kwa Zulu-Natal, Private Bag X01, Scottsville, 3209, Pietermaritzburg, South Africa.

4 Ethiopian Institute of Agricultural Research, P.O. Box 2003, Addis Ababa, Ethiopia

*Corresponding Author E-mail:

 

ABSTRACT:

Yams (Dioscorea spp.) are food security and socioeconomic importance crop in different areas of the world. Although it is cultivated and consumed in sub- Saharan Africa, still neglected by scientific research and development program in many countries including in Ethiopia. To fill in the knowledge gaps, the present study conducted at Jimma Agricultural Research Center during 2015. The objectives of the study were to characterize and assess the level of diversity within farmers and reference collection of yam landraces collected from major growing areas of Southwest Ethiopia. Thirty-six landraces of yam tested by using 6 x 6 simple lattice design with two replications. Data on 32 qualitative morphological traits collected and subjected to multivariate analyses. Cluster analysis based on qualitative characters revealed seven distinct clusters with varying sizes and presence of variability, based on their foliar and subterranean traits which will be highly useful in the genetic improvement. The result of the Shannon-Weaver diversity index (H`) indicated, the existence of a high level of diversity among Dioscorea spp. landraces based on the frequency distribution of phenotypic traits that considered. The results of PCA indicated that characters that have a good contribution to the variability. The first seven principal components explained 88.4% of the total variation, while PC-I and PC-II accounted 55.30% of the total variability. Thus, this utmost phenotypic variability between landraces is vital for hybridization and to produce potential and meaningful hybrids and desirable segregants of yams in Ethiopia.

 

KEYWORDS: Cluster, food security, hybridization, PCA.

 

 


 

INTRODUCTION:

Yam is a multi-species crop that belongs to the genus Dioscorea family (Coursey, 1967, Tamiru et al. 2007). The genus Dioscorea belongs to the monocotyledonous family Discoreaceae, the most imperative family within the order Dioscoreales (Burkill, 1960, Ayensu and Coursey, 1972, Dansi et al. 1999). It is grown in Africa, India, Southeast Asia, Australia and tropical America with more than 600 species (Jayasurya, 1984, Wilkin, 1998, Mignouna et al. 2002, Mulualem and Mohammed, 2013). All species are the tropical origin, are grown for their edible tubers and bulbils. About ten species are food yams and cultivated as staples for millions of people throughout the tropics (Hahn and Hozio, 1993, Dansi et al. 2013, Sesay et al. 2013).

 

Among from all species, Discorea alata, Discorea bulbifera, Discorea cayenensis and Discorea rotundata complex are the most widely cultivated and have real economic significance in Africa (Lebot, 2009, Asiedu and Alieu, 2010, Norman et al. 2012). Even though yams are cultivated mainly in most tropical countries, the most important species are originated from Ethiopia (Coursey, 1967, Zeven and De Wet, 1982; Tamiru et al. 2011), and grown in African (Terauchi et al. 1992). Miege and Demissew (1997) described eleven Dioscorea species grown in Ethiopia. Besides, 23 indigenous yam types belonging to four Dioscorea species such as, D. bulbifera (aerial yam), D. alata (water yam), D. cayenensis and D. rotundata Complex are widely distributed in major growing areas of the country for food, medicinal use and to fill economic gaps during the absence of other crops in the field (Vavilov, 1951, Coursey 1967, Hildebrand, 2002). Furthermore, various Dioscorea species growing in the complex farming system as cultivated and wild forms with cereals and other root and tuber crops (Edwards, 1991).

 

Despite its contribution to food security, as medicinal, social and economic value, yams in Ethiopia have been poorly investigated and farmers’ distinguished their cultivated landraces on the bases of morphological traits by using their indigenous knowledge. Conversely, the existence of different vernacular names for the same cultivar of the species has created problems to classify landraces while avoiding duplicates for conservation (Karamura, 1998; Mulualem, 2008).

 

Morphological characterization is the first step in grouping and description of the crop (Smith and Smith, 1989). Various characterization techniques have been successfully used to classify and measure the pattern of phenotypic diversity in the relationship of crop landrace collections of economically important traits. Genetic diversity can be described by four levels of organization that is, among species, among populations, within populations and within individuals (Hunter, 1996). The use of multivariate statistical methods is an imperative strategy for classifying landrace, ordering variability for a large number of landraces or analyzing genetic relationships among breeding materials (Mohammadi and Prasanna, 2003). To enhance productivity and to promote the uses of yam landraces, better understanding on the patterns of variability and grouping of available landraces are needed to boost yam production, which minimizes the poverty and improves the livelihood of rural households. To utilize the indigenous yam genetic resource in Ethiopia and to analyze the diversity present in on farm, characterization, evaluation of the existed landraces and using multivariate analyses is essential. Cognizant to these facts, the present study was designed to constitute landrace groups based on morphological resemblance, assess the level of diversity within yam collection, identify the key traits contributing to the variability, and to find superior landraces for the future breeding program.

 

MATERIALS AND METHODS:

Study area:

The study conducted at Jimma Agricultural Research Center (JARC). The center located at latitude 7o 40.00' N and longitude 36o 47’.00’ E with an altitude of 1753 m.a.s.l. The area received mean annual rainfall of 1432 mm with the maximum and the minimum temperature of 26.50C and 12.00 0C, respectively. The soil of the study area is Eutric Nitosol (reddish brown) with pH of 5.3.

 

Experimental materials, design, and management:

The landrace studied consisted of 36 yam landraces collected from seven districts of Jimma, Sheka and, Bench-maji zones of Southwest Ethiopia. The experiment was laid out in 6x6 simple lattice design with two replications. Single row plots, with each row 7m long and spacing of 1.5m between rows, and 1m between plants within a row used. The layout and randomization of the field plots carried out based on the standard procedures outlined by Cochran and Cox (1957). Tubers of the same size and just started sprouting were used as planting material. Planting done on the ridges in the row. One month after planting, after the crop well established, the seedlings earthed up, frequent weeding and other agronomical operations were carried out consistently to entire treatments according to the farmer’s practices. Individual plants supported by the individual stake of dried coffee about 3.5-4.5 meters long above ground to encourage good canopy development. Five plants of the row from the middle were used for data collection and harvest.


 

Table 1. Descriptions the 36 yam landraces used for the study.

S. No.

Name of landrace

Zone

District

Latitude

Longitude

Altitude

1

59/02

Jimma

Mana

07040’37N

036049’10E

1718

2

68/01

Jimma

Dedo

07030’63N

036053’45E

1784

3

6/02

Bench maji

Sheko

06059’66N

035034’11E

1728

4

75/02

Jimma

Kersa

07040’43N

036048’76E

1734

5

3/87

Jimma

Manna

07040’58N

036048’75E

1731

6

56/76

Jimma

Manna

07041’89N

036048’06E

1837

7

54/02

Bench maji

Sheko

07002’03N

035032’77E

1892

8

46/83

Jimma

Dedo

07031’28N

036053’59E

1771

9

08/02

Jimma

Kersa

07040’46N

036048’79E

1740

10

116

Jimma

Dedo

07031’28N

036053’63E

1683

11

01/75

Sheka

Yeki

07011’30N

035026’22E

1171

12

06/83

Jimma

Dedo

07031’32N

036053’64E

1692

13

17/02

Sheka

Yeki

07011’27N

035026’26E

1176

14

07/03

Jimma

Dedo

07031’50N

036053’60E

1733

15

45/03

Jimma

Mana

07041’86N

036048’08E

1810

16

27/02

Jimma

Sekachekorsa

07035’06N

036041’91E

1877

17

37/87

Jimma

Mana

07041’87N

036048’13E

1940

18

10/002

Bench maji

Sheko

07002’91N

035029’76E

1668

19

76/02

Jimma

Kersa

07040’64N

036048’84E

1728

20

06/2000

Jimma

Sekachekorsa

07035’43N

036041’86E

1850

21

7/83

Jimma

Sekachekorsa

07035’06N

036041’91E

1898

22

58/02

Sheka

Yeki

07011’22N

035026’25E

1192

23

39/87

Jimma

Sekachekorsa

07035’42N

036042’94E

1885

24

32/83

Jimma

Shebesombo

07026’74N

036024’01E

1372

25

24/02

Jimma

Shebesombo

07026’75N

036024’07E

1379

26

2/87

Jimma

Shebesombo

07026’76N

036024’12E

1365

27

60/87

Sheka

Yeki

07011’72N

035026’48E

1199

28

15/2000

Bench maji

Sheko

07004’13N

035037’74E

1320

29

34/87

Jimma

Dedo

07031’37N

036053’44E

1911

30

21/02

Jimma

Sekachekorsa

07036’48N

036045’09E

1785

31

57/76

Bench maji

Sheko

07002’88N

035029’74E

1654

32

0001/07

Jimma

Shebesombo

07026’74N

036024’12E

1367

33

0004/07

Jimma

Kersa

07040’55N

036048’75E

1741

34

7/84

Bench maji

Sheko

07002’88N

035029’74E

1661

35

7/85

Sheka

Yeki

07014’30N

035026’17E

1173

36

06/2001

Bench maji

Sheko

06059’69N

035034’09E

1387

 


Morphological data collection:

A descriptor of yam (Dioscorea spp.) developed by Bioversity International (IPGRI, 1999) followed for data collection. A total of 32 qualitative characters measured for this study. Data recorded from the middle of five plants of the row, and the average value used for statistical analysis. Munsell color chart used for color identification. The lists of qualitative characters presented as follow:

Leaf color: 1= yellow-green, 2= pale-green,

3=dark-green, 4= purplish-green, 5=purple,99=other

Leaf vein color upper surface: 1= green,

2= yellow-green, 3=pale-purple, 4= purple, 99=other

Leaf vein color lower surface: 1= green,

2= yellow- green, 3= pale- purple, 4= purple, 99= other

Leaf margin: 1=Entire 2= Serrate

Leaf margin color: 1= green, 2= purple,

3= yellow-green, 99= other

Leaf shape: 1= ovate, 2= chordate 3= chordate-long, 4=chordate-broad, 5= sagittate

Leaf apex shape: 1= obtuse 2= acute, 3=emarginated

Hairiness of leaf surface: 0= present, 1= absent

Leaf position: 1= alternate, 2= opposite

Leaf size: 1= Small, 2= Medium, 3= Large

Leaf density: 1= Low, 2= Medium, 3= High

Leaf lobations: 1= shallow, 2=deep

Waxiness: 0= absent 1= present

Tip color: 1= light-green, 2= dark-green, 3= purple,

4= red, 99=other

Petiole color: 1= all green with purple base,

2= all green with purple leaf junction, 3= all green with purple at both ends, 4= all purplish green with purple base, 5= all purplish green with purple leaf junction, 6= all purplish green with purple at both ends,7= green, 8= purple, 9= brownish green, 10= brown, 11= dark brown, 99=other.

Petiole wing color: 1= green,

2= green with purple edge, 3= purple, 99= other

Twinge direction: 1= clockwise, 2= anticlockwise

Vine color: 1= yellowish, 2= green,

3= light-green, 4=purple, 99=other

Wings on vine: 1=present, 2= absent

Wing color: 1= green, 2= green with purple edge,

3= purple 99= other

Spines: 1= present, 2= absent

Spine shape: 1= straight, 2= curved

Color at spine base: 0= present, 1= absent

Spine on the vine base: 0= none, 3= Few, 7=many

Tuber shape: 1= round, 2= oval, 3= oval-oblong,

4= cylindrical, 5= flattened, 6= irregular, 99= other

Tuber skin color: 1= grayish, 2= light-brown,

3=dark-brown, 4= 0ther

Tuber branching: 0= none, 1= slightly branched,

2= branched, 3= highly branched

Tuber surface texture: 1= smooth, 2= rough

Tuber flesh color: 1= white, 2= yellowish-white,

3= yellow, 4= orange, 5= light-purple, 6= purple

7= purple with white, 8= white with purple, 9= outer purple/ inner white, 99= other

Hairiness of tuber surface: 0= absent, 1=small, 2=medium, 3= large

Flower: 0= present, 1 absent

Flesh color at central transverse cross section: 1= white, 2= yellow- white, 3= yellow, 4= orange, 5= light- purple, 6= purple, 7= purple with white, 8= white with purple, 9= outer purple/inner yellowish, 99 = other

 

Statistical analysis:

Cluster analysis based on qualitative traits:

Clustering was done using the Statistical Analysis System (SAS) package (version 9.0 of SAS Institute Inc, 2000) based on Un-weighted Pair Group Methods with Arithmetic average (UPGMA). The number of clusters was determined by looking into two statistics namely, pseudo F and pseudo T2. The number of the cluster decided where the pseudo F statistics combined with the small value of pseudo T2 and large pseudo T2 statistical for the next cluster fusion (Milligan and Cooper, 1985). The dendrogram constructed by UPGMA (Afifi and Clark, 1990).

 

Frequency distribution and Shannon-Weaver diversity index (H’):

The frequency distribution is a systematic way of ordering a set of data from the lowest to the highest value showing the number of occurrences (frequency) at each value or range of values. In the latter, the distribution is called a relative frequency distribution. The Shannon-Weaver diversity index was used to determine the diversity of the landraces collected from different districts of Southwest Ethiopia by using the frequency of distributions and the number of phenotypic classes (Hennink and Zeven, 1991). The index defined as:

 

 

Where pi is the proportion of the total number of individuals (landrace) in the ith class and, S is the number of phenotypic classes.

 

The Shannon Weaver index values (H’) can ranged from 0 to ~ 4.6 using the natural log (versus log10). A value near 0 indicated that every species in the sample are the same. Conversely, a value near 4.6 showed the numbers of individuals evenly distributed between the species (Hennink and Zeven, 1991).

 

Principal component analysis:

The principal component analysis performed by using a correlation matrix by employing SAS version 9.0 (SAS, 2000). The objective of this analysis was to reduce the observed variables into a small number of principal components that accounted for most of the variance in the observed variables. The first step in PCA is calculating the eigen values, which define the amount of total variation that displayed on the PC axes. The first PC groups most of the variability present in the original data relative to all remaining PCs. The second PC explains most of the variability not summarized by the first PC and uncorrelated with the first, and so on (Mohammadi and Prasanna, 2003).

 

RESULTS AND DISCUSSION:

Cluster analysis:

Grouping of landraces based on their similarity is essential. In the present study, this approach was adopted to cluster the landraces into seven different groups with different sizes based on 32 qualitative characters (Table 2). A dendrogram summarize genetic similarly among 36 Dioscorea landraces based on qualitative characters are given in Figure 1. The number of landraces belonging to each cluster was diverse and varied from one in cluster VII to 11 in cluster I and II (Table 2).

 

Cluster I was the largest and consisted 11(30.55%) of the total landraces. Of these, nine from Jimma zone (3 each from Dedo and Seka chekorsa, two from Kersa and one from Shebe- sombo), and one landrace each from Bench-Maji and Sheka collections. Landraces grouped under this cluster have mainly identified by dark-green leaf, green vein on upper and lower surface, entire and yellow-green leaf margin, chordate leaf, acute leaf apex, opposite leaf position, medium leaf size, medium leaf density, light-green tip and petiole, cylindrical tuber shape, light-brown and slightly branched tuber, large hair rough tuber surface with white with purple flesh color at the central transverse.

 

Likewise, Cluster II also accommodated 11 landraces (30.55%), six from Bench-Maji and five from Jimma collections. Landraces failed into this cluster different from cluster I by having yellow-green vein on upper surface, obtuse leaf apex, small leaf size, all green with purple edge petiole, green vine, irregular and branched tuber with medium hair, rough tuber surface and light -purple flesh color at the central transverse. Besides, four landraces (11.11%) grouped under cluster III, all from Sheka and Jimma collections. They typically possessed yellowish and dark- green leaf, yellowish and green leaf vein on upper surface, yellow-green leaf margin and leaf vein on lower surface, all green with purple at both ends of petiole, obtuse leaf apex, purple tuber flesh, dark- brown tuber skin and purple with white flesh color at the central transverse.

 

Three landraces (8.33%) grouped under cluster IV, all from Jimma (2 from manna and one from Shebe-sombo) zone. Predominantly, landraces differ from the other clusters by having shallow and deep leaf lobs, dark-green tip color, all green with purple at both ends petiole color, clockwise and anti-clockwise twining direction, light-green vine, green wing and flattened tuber shape. Some landraces categorized under this cluster, produce flower at maturity. Finally, seven landraces were (19.44%) grouped under cluster V, VI and, VII, two from Sheka and five from Jimma collection. All landraces typically possess the combination of all characters described under the above four clusters. The results indicated landraces collected from diverse agro-ecological areas of Southwest Ethiopia; nevertheless, landraces from the same or different zones fall into different clusters and showing different genetic make-up. Thus, it may be of considerable importance to enlarge the genetic bases of yams by a sustainable and continual collection of landraces throughout the major growing areas of the country for further genetic enhancement of the crop. Dewey and Lu, (1959) and Kifle (2006) who further confirmed that while selecting landraces from a particular cluster, the inter-cluster distance and cluster mean performance of traits should be taken into consideration.

The cluster means of 19 quantitative characters were assessed based on clusters formed by 32 qualitative characters and showed that cluster VII had the highest value in most of the characters that considered in this study; for example, longest leaves, longest leaf lobs, longest vine, longest tip and widest leaves, highest number of tuber and vine hill-1and vine fresh weight (Table 3). Cluster IV showed high performance among the characters that considered. For example had highest petiole length, distance between lobs, tuber length, number of internodes vine-1, number of vine hill-1, tuber fresh weight, tuber dry weight, and harvest index. Cluster I showed the highest vine fresh and dry weight. Cluster III had the highest days of maturity. However the rest of cluster had the average performance of the traits considered.

 


 

Table 2. Clusters of Dioscorea spp. landraces based on qualitative traits

Clus-ters

Number of land races in each cluster

Serial number

Name of landraces in each cluster

Major characteristics

I

11

29,36,19,26,16,4, 8,30, 12, 27 and 21.

34/87, 06/2001, 76/02, 2/87, 27/02, 75/02, 46/83, 21/02, 06/83, 60/87, and 7/83

LC=dark green, LVCUS= green, LVCLS= green, LMC=yellow green, LM= entire, LS= chordate, LAS= acute, LPO= opposite, LSi=medium, LD=medium, LLO= shallow, Tic= light green, PC=light green with purplish leaf junction, PWC=green with purple edge, Twdir=clockwise, VC= yellow green, Wic= green, Tsh= cylindrical, Tsc= light brown, TFC=light brown, TBr.= slightly branched, TStex= rough, HoTs= large and FCCS= white with purple.

II

11

23,24,3, 34, 28, 31,7,18,25,2 and 5.

 

39/87, 32/83, 6/02,7/84, 15/2000, 57/76, 54/02, 10/002, 24/02, 68/01and 3/87.

LC=dark green, LVCUS= yellow green, LVCLS= green, LMC=yellow green, LM= entire, LS= chordate, LAS= obtuse, LPO= opposite, LSi =small, LD=medium, LLO= shallow, Tic= light green, PC= all green with purple edge, PWC= green, Twdir= clockwise, VC= green, Wic= green, Tsh= irregular, TFC=light brown, Tsc= light brown, TBr.= branched, TStex= rough, HoTs= medium and FCCS= light purple.

III

4

22, 35, 10 and 20.

58/02, 7/85, 116 and 06/2000.

.

LC=yellowish and dark green, LVCUS=yellow and green, LVCLS= yellow green, LMC=yellow green, LM= entire, LS= chordate, LAS= obtuse, LPO= opposite, LSi=small, LD=medium, LLO= shallow, Tic= light green, PC= all green with purple at both ends, PWC=green, Twdir= clockwise, VC= light green, Wic= green, Tsh= oval oblong, TFC=purple, Tsc= dark brown, TBr.= branched, TStex= rough, HoTs= medium and FCCS= purple with white.

IV

3

6, 32 and 1.

56/76, 0001/07 and 59/02

 

LC=pale green, LVCUS=yellow green, LVCLS= yellow green, LMC= green, LM= entire, LS= cordate, LAS= obtuse, LPO= opposite, LSi=medium, LD=medium, LLO= shallow and deep, Tic= dark green, PC= all green with purple at both ends, PWC=green, Twdir= clockwise and anti clockwise, VC= light green Wic= green, Tsh= flattened, TFC=outer purple inner white, Tsc= dark brown, TBr.= branched, TStex= rough, HoTs= medium and FCCS= purple with white.

V

4

13, 14, 15 and 17.

17/02, 07/03, 45/03 and 37/87.

LC= green, LVCUS=yellow and green, LVCLS= yellow green, LMC= green, LM= entire, LS= chordate, LAS= acute, LPO= opposite, LSi=small, LD=high, LLO= shallow, Tic= green, PC= all green with purple at both ends, PWC=green with purple edge, Twdir= clockwise, VC= light green, Wic= green, Tsh= irregular, TFC=purple with white, Tsc= dark brown, TBr.= branched, TStex= rough, HoTs= small and FCCS= purple with white.

VI

2

9 and 11

08/02 and 01/75.

 

LC=pale green, LVCUS=yellow green, LVCLS= yellow green, LMC=green, LM= entire, LS= chordate, LAS= obtuse, LPO= opposite, LSi=medium, LD=medium, LLO= shallow and deep, PC= all green with purple at both ends, PWC=green, Twdir= clockwise and anti clockwise, VC= light green, Wic= green, Tsh= round and oval, TFC=light purple, Tsc= dark brown, TBr.= slightly branched, TStex= rough, HoTs= medium and FCCS= purple with white.

VII

1

33

0004/07.

LC= yellow green, LVCUS=yellow green, LVCLS = yellow green, LMC= green, LM= entire, LS= chordate, LAS= obtuse, LPO= opposite, LSi= medium, LD= medium, LLO= shallow, Tic= green, PC= all green with purple at both ends, PWC=green with purple edge, Twdir= clockwise, VC= green, Wic= green, Tsh= round, TFC=purple with white, Tsc= dark brown, TBr.= branched, TStex= rough, HoTs= large, and FCCS= purple with white.

LC=Leaf color, LVCUS= leaf vein color upper surface, LVCLS= leaf vein color lower surface, LMC= Leaf margin color, LM= Leaf margin, LS=Leaf shape, LAS = Leaf apex shape, LPO=Leaf position, LSi=Leaf size, LD=Leaf density, , LLO=Leaf lobation, Tic= Tip color, PC=Petiole color, PWC= petiole wing color, Twdir= twing direction, VC=vine color ,Wic= wing color, TSh=tuber shape, Tsc=Tuber skin color, TBr= tuber branching, TStex= tuber texture, TFC=Tuber flesh color, HOTs= hair on tuber surface, FCCS= flesh color at central transverse

 

Table 3. Cluster means of 19 quantitative traits of 36 Dioscorea spp. based on qualitative characters

Cluster

Characters

LL

LW

PL

LLo

DBL

VL

IL

TiL

NIPV

NTPH

I

10.3

4.24

10.2

2.22

3.51

251.8

9.61

2.59

25.53

4.41

II

10.5

4.23

10.1

1.90

3.36

255.3

9.62

2.50

26.94

4.32

III

10.2

4.36

11.5

1.45

3.40

246.1

9.56

2.52

23.88

3.93

IV

11.6

4.60

9.93

2.78

3.66

256.4

9.75

2.87

25.81

4.13

V

9.87

3.94

9.28

1.54

3.24

265.4

9.80

2.32

28.88

4.58

VI

10.9

4.08

10.3

2.60

3.55

255.1

10.1

2.63

22.90

3.89

VII

12.6

4.80

11.9

1.68

3.15

257.0

10.7

2.29

24.55

3.80

Continued Table 3.

Cluster

Characters

DM

NVPH

TL

TDi

VFW

VDW

TFW

TDW

HI

I

137.4

4.40

38.4

14.48

12.64

3.37

29.54

20.74

67.41

II

133.1

4.40

38.5

14.17

13.35

3.03

26.34

21.26

63.15

III

135.4

4.20

38.2

16.08

11.42

3.17

23.80

19.09

65.45

IV

149.2

4.40

38.9

15.68

9.56

3.04

39.20

22.13

79.21

V

142.5

4.20

39.2

15.62

12.89

2.91

35.30

20.40

72.51

VI

145.5

4.30

40.2

15.69

12.28

2.81

37.60

21.35

75.48

VII

136.9

4.20

42.7

15.68

15.44

3.21

31.60

18.31

66.91

LL=Leaf length(cm); LW= Leaf width(cm); PL= Petiole length (cm); LLo = Length of leaf lobe (cm); DBL= Distance between lobs (cm); VL= Vine length(cm);IL= Internodes length (cm);TiL= Tip length (cm);NIPV= Number of internodes/vine; NTPP= Number of tubers/hill; DM= Days to maturity;NVPH= Number of vine per hill;TL=Tuber length(cm); TDi= Tuber diameter (cm); VFW= Vine fresh weight (t/ha); VDW=Vine dry weight (t/ha);TFW=Tuber fresh weight(t/ha); TDW=Tuber dry weight(t/ha)and HI= Harvest index (%).

 


 

Figure 1. Dendrogram showing hierarchical clustering patterns of 36 Dioscorea spp. landraces (UPGMA) based on 32 qualitative characters

 

Comparison of yam landraces between zones and districts:

To know whether landraces restricted to the zones/districts or not, using comparison analysis was carried out between landraces and area of collection from southwest Ethiopia based on cluster analysis (Table 2). The results revealed that four landraces namely: 56/76, 59/02, 0001/07 and 0004/07 restricted to Jimma zone (Manna, Kersa and Shebe-sombo). Besides, landrace, 08/02 and 01/75 restricted to Jimma (Kersa) and Sheka zone (Table 4). The four landraces grouped under cluster IV and VII which are found mostly in the Jimma zone are absent in Bench-Maji and Sheka zones. This is due to the geographical differences between the districts. This is true for similar and dissimilar districts. Similar districts belong to the same boundary and have high possibilities to share genetic materials between farmers; however, districts not bounded by the same boundary had different landraces. However, the association hardly follow similar tendency, as the most similar zones of Jimma, Bench-Maji and Sheka, Dedo and Sheko and districts Kersa manna and Shebe-sombo were also among those located far apart. About 11(30.55%) of the total landraces grouped under cluster I found in all zones and districts except manna. This might be due to all districts have a similar agro ecology that was conducive for different landraces. This is also further indicated that landraces that found in one district/zone can adapt in another district when the possibility of exchange materials between farmers for conservation strategy to design.


 

Table 4. The distribution of yam landraces and areas of collection based on cluster analysis

Zone

Districts

Clusters

Total

I

II

III

IV

V

VI

VII

Jimma

Dedo

3.0

1.0

1.0

0.0

1.0

0.0

0.0

6.0

Kersa

2.0

0.0

0.0

0.0

0.0

1.0

1.0

4.0

Manna

0.0

10

0.0

2.0

2.0

0.0

0.0

5.0

Seka-chekorsa

3.0

1.0

1.0

0.0

0.0

0.0

0.0

5.0

Shebe-sombo

1.0

2.0

0.0

1.0

0.0

0.0

0.0

40

Bench Maji

Sheko

1.0

6.0

0.0

0.0

0.0

0.0

0.0

7.0

Sheka

Yeki

1.0

0.0

2.0

0.0

1.0

1.0

0.0

5.0

Total

11.0

11.0

4.0

3.0

4.0

2.0

1.0

36.0

 


Phenotypic traits distribution:

Individual characters differed in their patterns of distribution and amount of variation among the 36 landraces. Most of the landraces in this study exhibited variation in foliar and subtraninnian plant parts are given in Figure 2.

 

Leaf color varied between landraces collected from the same and different districts. The dominant colors are being dark-green (61.11%), pale-green (25.00%) and, yellow-green (13.89%). No landraces with purple leaves on both surfaces observed. This may probably an adaptation for increasing the photosynthesis rate. A similar distribution found in the color of leaf vein upper surface. However, (88.89 %) of the landraces had yellow-green and (11.11%) had green leaf vein upper surface. Yellow-green and green leaf vein lower surface were observed for 83.33 and 16.67% of the landraces, respectively, with simple, entire and long petioles. Fifty percent of the landraces had green leaf margins, whereas, 27.78% had yellow-green leaf margins with an opposite leaf arrangement, while, 66.67 and 33.33% of the landraces had acute and obtuse leaf apex shape (Table 5). Most landraces (55.55%) having medium leaf size with chordate shape (66.67%), high leaf density (77.78%), shallow (86.11%) leaf lobe, light-green (63.89%) tip color. Thirty-three percent of the landraces had a purplish-green petiole with purple base, whereas, 63.89% had green petiole with a purple edge and, petiole wing color (Table 5).

 

The predominant vine color was light green (58.33%), while the remaining (41.67%) of the landraces had green vines with a few purple spots. Most of the landraces (94.44%) having clockwise twining direction at emergence. Few landraces (25%) produce spine on their vine with variable shape; 22.22% had curved, and, 8.33% had a straight shape, and highly associated with the wildness of the landraces. In wild type landraces spines distributed on the surface of vine and tuber in different amount and variable in size. Landraces collected from the same and different districts showed differences in the above vegetative plant parts (Figure 2). Besides, the variation in foliar before and after maturity observed among landraces. This also indicated the wide range of variation in different traits of yams in southwest Ethiopia. Thus, it needs strong attention in respect to conservation of yam genetic resources in Ethiopia.

 

Tuber shape of the landraces varied from irregular (36.11%) to oval (8.33%). The predominant tuber flesh color was white with purple (25.00%), followed by outer purple/inner white (22.22%), purple (19.44%) and, purple with white (13.89%) with dominant light and dark brown tuber skin color. Although, most of the landraces (44.44%), considered in this study exhibited branching tuber with rough (77.78%) and smooth (22.22%) surface. The flower of landraces predominantly produced spike type of inflorescent (25.0%) the other landraces hardly produced flower during the entire growing period. The predominant tuber flesh color at central transverse cross-section was white (38.89%). The other flesh colors observed included white with purple (19.44%) and (13.89%) of landraces produced similar color, for example, light purple, purple and purple with white flesh color. This result in line with Tamiru et al. (2006), who reported that there is a wide range of variability of tubers among Dioscorea species in south Ethiopia. Furthermore, a similar result was reported by Nebeyu (2003) in cassava (Manihot esculenta Cranz) and Dagne (2007) in taro (Colocasia esculenta).

 


 

A. The vegetative plant part

        

 

 

 

 

 

 

 

B. The reproductive plant part

             

                                         A seed of yam                                                   A seed                               Flower

 

C Tuber collected from different landraces

 

Figure 2. Vegetative, reproductive and storage organ (tubers) of yams of different landrace collections from Southwest Ethiopia.

 


The Shannon-Weaver Diversity Index (H')

Assessment of genetic diversity is an important aspect of any crop improvement program to identify high yielding landraces (Rhman and Munsur, 2009). In the present study, the Shannon-Weaver diversity index (H’) was adopted to compute the diversity of Dioscorea spp. based on the frequency distributions of 32 qualitative morphological characters. The result of ‘H’ value for all observed phenotypic characters showed a high level of diversity among 36 Dioscorea spp landraces, which ranged from 0.21 for vine twining direction to 1.64 for petiole color (Table 5). Besides, the overall mean of ‘H’ value of 0.72 confirmed the existence of phenotypic diversity among yam landraces from southwest Ethiopia. This result was also in agreement with the works of Tamiru et al. (2011) who found an average level of diversity in yam collection from South Ethiopia and Silvia et al. (2006) in yam collection from Colombian.

 

 

 

High ‘H’ value indicates a relatively high level of diversity and evenly distribution of landraces (Hennink and Zeven, 1991; Kifle, 2006). Furthermore, a lower level of diversity was noticed on foliar qualitative traits (Table 5). This showed that subtraninian qualitative traits had a greater influence on the phenotypic diversity among the Dioscorea spp. landraces than the foliar traits. On the other hand, mono-morphism observed in some foliar characters; leaf margin, leaf position, wing on vine revealing that the contribution of these characters to the diversity was low and omitted these characters for principal component analysis. The low level of diversity may also indicate the narrow genetic base of the plant and the low level of sexual reproduction in yam. These results indicated the need for further study based on genetics (molecular) investigation on yam.

 

 

 

 

 

 

Table 5. Frequency distribution and the Shannon Weaver diversity indices (‘H’) of 32 qualitative traits of Dioscorea grown at Jimma, 2015.           

S. No.

Qualitative character

Index and description adopted

Frequency (%)

H’

1

Leaf color

Yellow green

13.89

0.92

Pale green

25.00

 

Dark green

61.11

 

2

Leaf vein upper color

Yellow green

88.89

0.35

Green

11.11

 

3

Leaf vein lower color

 Yellow green

83.33

0.45

Green

16.67

 

4

Leaf margin color

Green

50.00

1.03

Purple

22.22

 

Yellow green

27.78

 

5

Leaf margin

Entire

100.00

0.00

6

Leaf shape

Ovate

13.89

0.86

Chordate

66.67

 

Sagittate

19.44

 

7

Leaf apex shape

Obtuse

33.33

0.63

Acute

66.67

 

8

 

Hair on the leaf

Present

16.67

0.45

Absent

83.33

 

9

Leaf position

 Opposite

100.00

0.00

10

Leaf size

Small

25.00

0.99

Medium

55.55

 

Large

19.44

 

11

Leaf density

 Intermediate

22.22

0.53

High

77.78

 

12

Leaf lobation

Shallow

86.11

0.40

Deep

13.89

 

13

Waxiness on leaf

Absent

83.33

0.45

Present

16.67

 

14

Tip color

 Light green

63.89

0.85

Dark green

27.78

 

Purple

8.33

 

15

Petiole color

 All green with purple base

13.89

1.64

All green with purple leaf junction

8.33

 

 All purplish green with purple base

33.33

 

All purplish green with purple leaf junction

11.11

 

All purplish green with purple at both ends

25.00

 

Green

8.33

 

 

16

 

 

Petiole wing color

Green

16.67

0.90

Green with purple edge

63.89

 

Purple

19.44

 

17

Twing direction

Clockwise

94.44

0.21

Anticlockwise

5.56

 

18

Vine color

Green

41.67

0.68

Light green

58.33

 

19

Wing on vine

Present

100.00

0.00

20

 

Wing color

Green

52.78

0.69

Green with purple edge

47.22

 

21

Present/absent of wing

Present

30.55

0.61

Absent

69.45

 

22

Spine shape

Straight

8.33

0.79

Curved

22.22

 

None

69.44

 

23

Color at spine base

Absent

69.44

0.61

Present

30.56

 

24

Spine on vine

Few

25.00

0.96

Many

16.67

 

None

58.33

 

25

Tuber shape

Oval

8.33

1.39

Oval oblong

11.11

 

Cylindrical

36.11

 

Flattened

8.33

 

Irregular

36.11

 

26

Tuber flesh color

White

19.44

1.59

Purple

19.44

 

Purple with white

13.89

 

White with purple

25.00

 

Outer purple/ inner white

22.22

 

27

Tuber skin color

Light brown

50.00

0.69

Dark brown

50.00

 

28

Tuber branching

Slightly branched

13.89

1.26

Branched

44.44

 

Highly branched

27.78

 

None

13.89

 

29

Tuber surface texture

Smooth

22.22

0.53

Rough

77.78

 

30

Hairiness of tuber surface

Small

22.22

0.53

Medium

77.78

 

31

Flower

Present

25.00

0.56

Absent

 75.00

 

32

Flesh color at central transverse cross section

White

38.89

1.50

Light purple

13.89

 

Purple

13.89

 

Purple with white

13.89

 

White with purple

19.44

 

Overall Mean

 

 

0.72

 

Principal components analysis:

The patterns of variation and the relative importance of each trait in explaining the observed variability assessed through principal component analysis (PCA). In the present study, the principal component analysis was adopted based on 29 variables. The first seven principal components explained 88.4% of the total variation (Table 6). The first principal component (PCI) alone accounted for 32.5% of the total variation. Flesh color at central transverse, spine on vine base and tuber flesh color had the highest loadings on PCI. The second principal component (PC 2), explaining 22.8% of the total variation, was highly correlated with presence of spines on vine base and tuber flesh color, while PCIII associated with the spine on vine base, flesh color at central transverse, petiole and leaf color explained 12.9% of the total variation. The remaining PCs accounted 20.2% of the total variation, and mainly associated with petiole color, spine on vine base, tuber shape, flesh color at central transverse, tuber skin color and tuber branching (Table 6). From all the characters, tuber flesh color was found to be the most discriminative parameter differentiating landraces collected from southwest Ethiopia. To evaluate the scores of solitary landrace, PC1 and PC2 were plotted (Figure 3). All landraces distributed at the origin of the plot. The landrace 15/2000, 54/02 and 10/002 had the highest positive scores for both components and grouped to the top central corner of the plot. Conversely, landraces 75/02, 76/02, 27/02 and 59/02 had the lowest negative scores for PC-2 and the highest positive values for PC1 and grouped into the bottom right corner of the plot. The result of this study is consistent with the separation of landraces into two groups by UPGMA clustering (Figure 3).

 


 

Table 6. Eigen values, Proportion, Cumulative variance and component scores of the first seven principal components for qualitative traits in 36 yams from Southwest Ethiopia.

Variable

PC1

PC2

PC3

PC4

PC5

PC6

PC7

Eigen value

12.925

9.095

5.120

3.695

1.752

1.487

1.113

Proportion

0.325

0.228

0.129

0.093

0.044

0.037

0.028

Cumulative

0.325

0.553

0.682

0.775

0.819

0.856

0.884

Leaf color

-0.005

0.066

0.157

-0.037

0.148

-0.290

-0.113

Leaf vein color upper surface

0.037

0.032

-0.034

-0.128

-0.013

0.239

0.097

Leaf vein color lower surface

-0.013

0.029

-0.006

0.021

-0.009

0.018

-0.051

Leaf margin color

0.019

-0.024

-0.006

0.024

-0.134

-0.249

-0.466

Leaf shape

0.055

-0.075

-0.287

0.220

0.560

-0.535

0.060

Leaf apex shape

-0.043

-0.006

-0.038

-0.020

-0.071

0.123

0.105

Hair on leaf surface

0.010

-0.021

-0.019

-0.004

-0.027

0.010

-0.067

Leaf size

-0.003

-0.056

0.077

0.057

-0.091

0.128

-0.084

Leaf density

0.021

0.057

-0.034

-0.041

0.005

-0.023

-0.006

Leaf lobation

0.044

0.066

-0.012

0.021

-0.136

-0.043

0.014

Waxiness on leaf

0.008

0.050

0.007

0.057

0.105

-0.030

0.042

Tip color

0.046

0.066

-0.107

0.107

-0.039

-0.174

0.043

Petiole color

0.015

0.095

0.507

-0.710

0.220

-0.209

0.076

Petiole wing color

0.036

0.071

-0.049

0.091

0.024

-0.071

-0.247

Twining direction

-0.014

-0.006

-0.007

0.075

0.066

0.016

0.030

Vine color

-0.030

-0.045

0.018

0.002

0.010

0.063

0.129

Wing color

-0.029

0.011

-0.026

0.103

-0.101

-0.094

0.152

Presence/absence of spine

0.070

0.039

0.084

-0.008

0.081

0.108

-0.031

Spine shape

0.131

0.054

0.137

-0.016

0.124

0.164

-0.089

Color at spine base

0.062

0.022

0.078

0.027

0.123

0.100

-0.024

Spine on vine base

0.482

0.498

0.428

0.410

-0.165

-0.144

0.076

Tuber shape

0.008

0.062

-0.255

-0.269

-0.578

-0.458

0.338

Tuber flesh color

0.461

-0.812

0.258

0.094

-0.114

-0.103

0.083

Tuber skin color

0.020

-0.078

-0.051

-0.090

0.238

-0.071

0.119

Tuber branching

0.010

0.067

0.052

0.159

0.207

0.087

0.669

Tuber surface texture

-0.036

0.008

-0.042

0.010

-0.024

-0.013

-0.051

Hair on tuber surface

0.026

0.080

0.091

-0.040

-0.031

-0.213

-0.075

Flower

0.040

0.016

0.045

-0.016

0.073

-0.087

-0.096

Flesh color at central transverse

0.717

0.155

-0.496

-0.317

0.125

0.157

-0.061

 


 

Figure 3.The Bi-plot diagram of PCA I and PCA II of 36 yam landraces based on 29 qualitative traits.

 

 

CONCLUSION:

Analysis of Dioscorea spp. landraces based on phenotypic variability had a great contribution for better assessment of the landraces and identification of the plants with desired characteristics for breeding. Based on the result of the Shannon-Weaver diversity index, and cluster analysis revealed that maximum diversity existed between Dioscorea spp. landraces indicated the fact that hybridization among the landraces included with them would produce preeminent hybrids and desirable segregants. Besides, they appeared lack of reasonable degree of correspondence between groups of landraces and collected geographical location. To further investigate the genetic basis of the diversity revealed among Dioscorea spp. landraces, it is necessary to assess the existed landraces through additional collection from different growing areas over more seasons in different locations to get stable landraces for different environment.

 

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Received on 26.02.2019         Modified on 20.03.2019

Accepted on 05.04.2019       ©A&V Publications All right reserved

Res.  J. Pharmacognosy and Phytochem. 2019; 11(2):54-64.

DOI: 10.5958/0975-4385.2019.00011.6