Agro morphological diversity of Yams (Dioscorea spp.) Landraces from Southwest Ethiopia assessed through quantitative and qualitative traits

 

Tewodros Mulualem¹, 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.

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

 

ABSTRACT:

Yams (Dioscorea spp.) are an important crop widely cultivated for food, feed and medicine in different areas of the world. Knowledge on genetic diversity among yam landraces is essential for breeding and conservation strategies. The objective of this study was to assess the level of genetic diversity present among yam landraces using morphological traits. Thirty-six yam landraces were phenotyped at at Jimma Agricultural Research Center during 2015/16 growing season. The experiment was laid out in 6x6 simple lattice design with two replications. Data were collected on nine quantitative and ten qualitative traits, and subjected to hierarchal cluster, correlation and principal component analyses. A dendrogram was constructed using the unweighted pair group method with arithmetic mean. Tuber fresh weight showed a positive and significant association with tuber length and tuber diameter. The principal component analysis revealed five important principal components that accounted for 56.9% of the total variation observed among landraces. Principal components 1, 2, 3, 4 and 5, respectively, correlated with leaf length, leaf width and vine length A dendrogram revealed three main clusters of landraces. The most diverse landraces identified were 27/02, 21/02, 06/2000 and 68/02, which are useful for breeding and conservation. The diversity observed among the yam landraces could be useful in improvement of yams for various traits.

 

 

 

INTRODUCTION:

Yam (Dioscoria spp.) is a crop of major economic and cultural importance in tropical Africa, which accounts 95% of the total world production (FAO, 2005; Dansi et al., 2013). In sub-Saharan Africa, yam is the third most important staple food crop after cassava (Manihot esculenta Crantz) and sweet potatoes (Ipomoea batatas (L.) Poir) in terms of production and major source of food energy providing up to 285 calories per person per day for 300 million people (Abebe et al., 2013). In Ethiopia, Dioscorea species are adapted and widely distributed constituting of both cultivated and wild relatives (Terauchi et al. 1992; Tamiru et al. 2011). Further, 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).

 

Genetic variation in crop plants is essential for breeding. Maintenance of genetic diversity within and among crop species is critical for sustainable crop production, especially under low-input production conditions in marginal environments (Firew 2007). It is estimated that by 2050 the global human population will rise to 8.9 billion (FAO 2006). Consequently it is imperative to improve agricultural production and productivity to ensure food security to the ever-increasing human population (Alina et al. 2017). High genetic diversity provides security for farmers against biotic and a biotic stresses. Morphological characterization and evaluation of yams are mainly dependent on qualitative and quantitative traits (Bekele, 2014). Morphological characterization is the first step in the classification and description of crop genetic resources (Mulualem and Weldemichel, 2013). Various techniques have been successfully used to classify and measure the pattern of phenotypic diversity and relationship among landrace collections for economic traits. According to Dansi et al. (2013) assessment of phenotypic traits is cost effective, simple to score, requires less time and aids in selecting the correct ideotypes. Unlike DNA markers, morphological traits are influenced by the environment (Mulualem, 2016). Different studies have used phenotypic traits to effectively distinguish yam landraces (Bekele, 2014; Abebe 2008). Dansi et al. (1999) used both quantitative and qualitative traits for analysis of genetic diversity in yam from Benin Republic.

 

A wide range of genetic diversity was observed among yam landraces in Ethiopia (Hildebrand, 2002; Abebe et al. 2013). Loko et al. (2015) reported a broad range of morphological diversity among 177 yam accessions from Benin using agro morphological traits. Among the 38 South Ethiopian yam landraces studied by Tamiru (2006) only two were wild landraces. Morphological diversity analysis of yam landraces is required using a relatively greater number of samples, representative of the diverse yam growing areas. This will allow collect adequate information on the phenotypic performance and relatedness among the yam landraces originating from Ethiopia for effective and sustainable use of the yam genetic resources and future conservation. The objective of this study was to assess the level of genetic diversity present among yam landraces from Southwest Ethiopia using agro morphological traits.

 

MATERIALS AND METHODS:

Plant Materials:

A total of 36 yam landraces were collected from seven districts of Jimma, Sheka and Bench-Maji Zones of Southwest Ethiopia. The list of 36 yam landraces and their area of collections are presented in Table 2.

 

Study site:

A field study was conducted during the 2015/16 growing season at Jimma Agricultural Research Center (JARC) experimental station. The center is located at latitude 7^o 40.00' N and longitude 36^o 47’.00’ E with an altitude of 1753 meters above sea level (m.a.s.l.). The area receives mean annual rainfall of 1495mm with mean maximum and minimum temperatures of 29.0 ⁰C and 8.90 ⁰C, respectively (Table 1).

 

Table 1: Summary of climate data on the research site during the growth period

Month	Total rain fall (mm)		Mean temperature (oC)				Mean Relative humidity (%)		Mean Soil temperature  (0-30cm) (oC)		Mean Sunshine (hours)
			Minimum		Maximum
	Mean (1968-2015)	2016	Mean (1968-2015)	2016	Mean (1968-2015)	2016	Mean (1968-2015)	2016	Mean (1968-2015)	2016	Mean (1968-2015)	2016
Jan	44.9	56.2	12.1	10.4	27.6	25.6	58	69.4	21.8	23.9	7.4	7.8
Feb	41.8	61.6	12.8	12.5	28.4	29.0	57	53.0	22.5	24.1	7.0	7.4
Mar	98.9	97.8	13.6	12.5	28.2	25.6	59	61.4	23.2	24.1	6.5	8.2
Apr	136.7	96.5	14.7	11.3	27.6	25.9	63	59.3	23.4	23.8	6.4	8.0
May	191.3	192	14.8	11.9	26.4	27.0	68	67.0	23.1	23.8	6.5	6.7
Jun	218.1	185	14.5	10.6	24.7	26.9	74	66.0	22.3	23.4	5.1	5.4
Jul	229.5	205	14.5	12.0	23.2	23.9	79	62.7	21.2	20.8	3.4	4.9
Aug	235.3	210	14.3	13.6	23.5	24.6	79	68.0	21.3	23.1	3.8	3.9
Sep	210.6	250	14.2	15.6	24.7	24.8	75	76.0	22.1	23.8	5.1	5.6
Oct	122.7	63.3	11.9	12.8	25.9	27.0	69	65.0	22.6	23.8	7.2	7.2
Nov	63.8	22.1	10.4	11.8	26.5	28.5	67	58.0	22.3	23.9	8.0	6.4
Dec	58.4	53.2	8.7	8.9	27.1	28.8	61	53.0	21.8	23.6	7.9	6.7
Total	1652.0	1495	165.5	143.9	313.8	317.7	809.0	758	267.60	282.1	74.30	78.2
Mean	137.7	124	13.0	12.0	26.2	26.5	67.4	63.2	22.30	23.5	6.20	6.50

Source JARC, Metrology, 2017

 

Table 2: Summary of climate data on the research site during the growth period

S. No.	Name of landraces	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	Seka chekorsa	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	Seka chekorsa	07035’43N	036041’86E	1850
21	7/83	Jimma	Seka chekorsa	07035’06N	036041’91E	1898
22	58/02	Sheka	Yeki	07011’22N	035026’25E	1192
23	39/87	Jimma	Seka chekorsa	07035’42N	036042’94E	1885
24	32/83	Jimma	Shebe sombo	07026’74N	036024’01E	1372
25	24/02	Jimma	Shebe sombo	07026’75N	036024’07E	1379
26	2/87	Jimma	Shebe sombo	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	Seka chekorsa	07036’48N	036045’09E	1785
31	57/76	Bench maji	Sheko	07002’88N	035029’74E	1654
32	0001/07	Jimma	Shebe sombo	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

 

Experimental design and field establishment:

The tested landraces were evaluated using a 6 x 6 simple lattice design with two replications. Tubers of the same size which started sprouting were used as planting material. All other agronomical practices were followed according to the recommendations and farmers practices of the areas. Each yam plant was tended using dried coffee sticks of 3.5-4.5m long to provide support and induce good canopy and vine development. Five middle plants within a row were sampled and tagged for data collection and final harvest.

 

Data Collection:

Data were collected according to the descriptor yam (Dioscorea spp.) developed by Bioversity International (IPGRI, 1999). The quantitative characters measured were leaf length = (LL) measured from collar to the tip of the leaf at maturity (cm),  leaf width = (LW)  measured on the main vine from widest part at maturity (cm), petiole length =  (PL) measured from the base to the point of insertion of the leaf lob at maturity (cm), vine length (VL) measured from the ground to the tip of the vine at maturity (cm), Number of vine hill^-1= (NVPH) counted the number of vine at maturity, Tuber length = (TL) measured from the lower to the upper tip using venire caliper at harvest (cm), tuber diameter = (TDi) measured at the middle using venire caliper at harvest (cm), tuber fresh weight = (TFW) the tuber of all the plants of each plot were bulked and weighed at harvest (t/ha), tuber dry weight = (TDW)  estimated by drying 100g of fresh tuber in a forced air circulation oven at 70⁰C for about 72 hours and expressed in tonnes per hectare of the tuber fresh weight. The qualitative data included leaf color, which was recorded using the Munsell Colour Chart for Soil Scientists as 1= yellow green, 2= pale green, 3=dark green, 4= purplish green, 5=purple, 99=other. Leaf vein color upper surface was categorized as 1= green, 2= yellow green, 3=pale purple, 4= purple, 99=other. Leaf vein color lower surface was recorded as 1= green, 2= yellow green, 3=pale purple, 4= purple, 99=other. Leaf margin color was categorizes as 1=green, 2= purple, 3=yellow green 99= other.   Leaf apex shape was recorded as 1= obtuse   2=acute, 3=emarginated. Leaf shape was recorded as 1= ovate, 2= chordate   3= chordate-long, 4=chordate-broad, 5= sagittate. Petiole color was recorded as 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 was recorded as 1=green, 2= green with purple edge, 3= purple, 99=other. Vine color was categorized as 1=yellowish, 2=green, 3=light green, 4=purple, 99=other and twinge direction was recorded as 1= clockwise, 2= anticlockwise.

 

Data analysis

The collected data were subjected to correlation and principal component analysis (Jackson, 1991) using the multivariate analysis program in Genres statistical software (Genres, 2008). The quantitative data were analysed in SAS statistical program (SAS, 2000) using the general linear model procedure. A dendrogram was constructed based on the quantitative and qualitative data using the unweighted pair group method with arithmetic mean with Agglomerative Hierarchical clustering. Analysis of variance (ANOVA) was performed on quantitative traits using a mixed model. The following model for the simple lattice design was used:

 

Yijklm =µ+ ti +j + + yl +  +_,

 

Where, Y_ijklm = response of Y trait from the i^th landraces, j^th replication, µ= Overall mean effects, ti= Effects of i^th level of treatments, β= Effects of j^th level of replication, χ_k= Effects of K^th level of blocks within replications (adjusted for treatments), y_l = Effects of l^th level of intra block error, π_m= Effects of the m^th randomized complete block error and Σijklm= is a random error component. The frequency distribution of the qualitative traits was determined using SAS statistical program (SAS, 2000)

The phenotypic frequency data of the eight characters were analyzed using the Shannon–Weaver diversity index (H′) given as:

 

 

Where p_i is the proportion of the total number of individuals (landrace) in the i^th class and, S is the number of phenotypic classes.

 

RESULTS:

Analysis of variance:

The analysis of variance of nine quantitative traits is presented in Table 3. The result showed significant differences (P ≤ 0.01) in all of the quantitative traits measured. Highly significant differences (P ≤ 0.001) were also observed among the landraces for leaf length, leaf width, petiole length vine length, number of vine hill^-1, tuber length, tuber diameter, tuber fresh weight and tuber dry weight.

 

Table 3. Analysis of variance for quantitative characters

Trait	Replication (DF=1)	Mean square of landraces (DF=35)		Mean square of Blocks within Reps (Adj.) (DF=10)	Mean square of error		LSD	Efficiency relative to RCBD  (%)	CV (%)
		Unadjusted	Adjusted		Intra block (25)	RCBD (35)	0.01
LL	1.11	3.75	3.15**	1.49	0.34	0.67	1.81	159.24	5.59
LW	0.10	0.49	0.46**	0.25	0.07	0.12	0.85	138.69	6.53
PL	1.04	8.59	7.56**	4.36	3.23	3.55	4.89	102.43	17.5
VL	950.4	339.38	192.7**	418.22	34.29	143.9	18.3	332.63	2.29
NVPH	0.43	0.59	0.57**	0.32	0.21	0.24	1.26	104.14	10.9
TL	0.63	8.27	5.22**	6.97	2.22	3.58	4.54	134.85	3.84
TuDi	0.01	7.00	5.59**	1.57	1.96	1.85	3.82	94.36	9.40
TFW	13.66	333.03	219.1**	16.42	9.53	11.50	9.10	107.74	10.3
TDW	0.004	5.58	5.01**	1.09	1.04	1.06	2.78	100.06	4.93

** = Highly significant at 0.01 level of probability. ns= non significant

LL= Leaf length (cm), LW= Leaf width (cm), PL=Petiole length (cm), VL= Vine length (cm), NVPH= Number of vine hill^-1, TL= Tuber length (cm), TuDi= Tuber diameter (cm), TFW= Tuber fresh weight (t/ha) and TDW= Tuber dry weight (t/ha).  RCBD= Randomized complete block design, LSD= Least significant difference, CV=Coefficient of variation.

 

Table 4: Mean Minimum, Maximum and Standard Deviation and Coefficient of Variation for nine Quantitative Traits of 36 yam Landrace Collections

Landrace	LL	LW	PL	VL	NVPH	TuL	TuDi	TFW	TDW
59/02	12.68	5.13	7.13	262.33	4.28	39.22	15.84	40.40	23.36
68/01	11.91	4.67	14.0	265.42	3.90	41.83	15.76	30.00	21.48
6/02	14.16	5.00	12.88	267.00	3.50	41.35	16.74	35.10	21.62
75/02	11.07	4.54	8.77	280.85	4.80	41.17	14.88	33.80	21.36
3/87	10.07	4.16	7.98	251.85	3.80	38.03	13.12	16.80	23.57
56/76	11.82	4.44	11.53	267.25	4.20	41.04	16.40	53.80	20.96
54/02	8.65	3.72	9.58	267.00	4.50	37.77	12.40	30.40	22.45
46/83	9.83	3.84	13.28	257.25	3.80	37.37	13.92	28.55	20.81
08/02	11.81	4.66	10.17	256.50	3.90	41.81	18.00	41.40	20.74
116	9.05	4.66	11.15	250.10	3.90	40.33	16.08	29.60	19.81
01/75	10.09	3.50	10.5	253.75	3.88	38.66	13.38	33.80	21.97
06/83	10.2	4.08	9.4	252.25	4.30	38.66	13.76	44.00	21.80
17/02	10.16	4.31	9.77	240.50	3.40	36.49	17.20	49.20	18.14
07/03	9.29	3.00	9.8	263.50	4.20	39.79	15.04	24.00	13.51
45/03	11.28	4.86	11.73	260.75	4.60	40.13	17.76	37.40	18.47
27/02	10.93	4.49	12.38	271.50	4.30	43.83	15.92	47.40	18.86
37/87	8.75	3.58	5.82	296.75	6.10	40.42	12.48	30.60	22.50
10/002	10.28	4.43	9.6	263.85	5.00	38.72	15.60	63.00	27.83
76/02	10.17	4.06	8.23	247.00	4.40	37.13	12.16	33.40	23.33
06/2000	9.67	4.08	11.83	240.38	4.10	38.08	13.92	45.60	19.70
7/83	10.78	4.72	11.57	254.25	4.60	38.13	16.48	26.80	19.10
58/02	9.71	4.05	10.23	241.75	3.93	35.56	19.52	29.20	16.93
39/87	12.34	4.73	13.5	258.50	4.10	39.89	16.08	20.76	11.40
32/83	9.62	4.05	8.10	242.25	3.70	36.08	13.68	28.17	16.20
24/02	8.28	3.48	7.48	259.25	4.70	37.61	12.72	19.40	10.22
2/87	11.2	4.42	12.92	239.00	4.00	37.01	14.48	20.53	12.80
60/87	10.65	4.58	11.12	254.25	5.10	39.71	14.64	27.80	20.30
15/2000	11.86	4.22	8.17	243.25	4.33	38.06	12.10	20.86	11.80
34/87	10.72	4.16	8.17	235.00	4.20	36.06	12.64	16.80	12.55
21/02	9.76	4.30	9.92	237.50	4.50	35.69	16.72	28.40	20.61
57/76	9.88	4.42	10.45	246.35	5.10	36.90	12.72	32.00	19.17
0001/07	10.2	4.23	11.12	239.75	3.90	36.69	9.11	23.40	12.06
0004/07	10.04	4.33	10.78	243.05	4.50	36.79	10.92	27.70	20.62
7/84	8.77	3.61	8.92	243.75	4.92	37.19	13.78	23.67	12.71
7/85	12.39	4.63	12.6	252.25	3.80	39.02	12.39	19.60	11.91
06/2001	8.53	3.50	6.15	241.25	4.50	37.90	10.61	14.40	9.84
St.div.	1.13	0.47	2.07	13.33	0.53	1.99	2.28	11.07	4.53
Mean	10.46	4.24	10.19	254.09	4.30	38.61	14.42	31.33	18.35
Minimum	8.28	3.0	5.82	235.0	3.4	35.56	9.11	14.4	9.84
Maximum	14.6	5.13	14.0	296.75	6.1	43.83	19.52	63.0	27.83
LSD (0.01)	1.81	0.85	4.89	18.3	1.26	4.54	3.82	9.10	2.78
CV%	5.59	6.53	17.50	2.29	10.9	3.84	9.4	10.3	4.93

 LL= Leaf length (cm), LW= Leaf width (cm), PL=Petiole length (cm), VL= Vine length (cm), , NVPH= Number of vine  hill^-1,TL= Tuber length (cm), TuDi= Tuber diameter (cm), TFW= Tuber fresh weight (t/ha) and TDW= Tuber dry weight (t/ha).  St.div-= Standard deviation; CV= Coefficient of variation (%) and LSD= Least Significant Different

 

Among the quantitative traits measured, highly significant differences (P ≤ 0.001) were observed amongst yam landraces with respect to leaf length (Table 4). The mean leaf length ranged from 8.28 to 14.6 cm. Landraces that exhibited tall leaves were 6/02, 59/02, 39/87 and 7/85, while 24/02, 06/2001, 54/02 and 7/84 recorded short leaf lengths. Leaf width varied between 3 and 5.13cm with a mean of 4.24 cm (Table 4). Landraces that produced broad leaf were 59/02, 6/02 and 45/03. Petiole length ranged from 5.82 to 14 cm among landraces with a mean of 10.19 cm (Table 4). Landraces 68/01, 46/83, 2/87 and 6/02 had tall petiole length. Landraces 37/87, 75/02, 27/72 and 56/76 recorded the highest vine length with 296.75, 280.85, 271.5 and 267.25 cm, respectively. Highly significant (P < .001) differences were observed among yam landraces with regards to number of vine hill^-1. The lowest mean number of vine hill^-1 of 3.4 and 3.50 were recorded for landraces 17/02 and 68/01, respectively; whereas, the highest number of vine hill^-1 was recorded for 37/87 with a mean value of 4.3. Four yam landraces namely 27/02, 68/01, 08/02 and 6/02 recorded the highest mean tuber length values of 43.83, 41.83, 41.81 and 41.35 cm, respectively.  The mean tuber diameter ranged from 9.11 to 19.52 cm. Landraces that exhibited wider tuber were 58/02, 08/02, 45/03 and 17/02, while 0001/07, 06/2001 and 0004/07 recorded lowest tuber diameters. Tuber fresh weight varied from 14.4 t/ha (landrace 06/2001) to 63 t/ha (landrace 10/002). The lowest mean tuber dry weight of 9.84 and 10. 22 t/ha were recorded for landraces 06/2001 and 24/02, respectively

 

Correlation analysis among phenotypic traits:

Storage tuber yield and related traits were analyzed using pair-wise rank correlations coefficients. The results and association of the quantitative traits are reported based on the significance levels of 5% (p < 0.05) and 1% (p < 0.01) (Table 5). Leaf length was significantly and positively correlated with vine length, tuber fresh and dry weight, and was negatively correlated with number of vine per hill. It was further positively and significantly correlated with leaf width, petiole length, tuber length and tuber diameter. Leaf width was significantly positively associated with petiole length, tuber length and tuber diameter. Petiole length showed significant and negative correlation with number of vine per hill, and significant and positive correlation with tuber diameter. Vine length was significantly correlated with number of vine per hill, tuber length and tuber dry weight. Tuber length was positively correlated with tuber diameter and tuber fresh weight. Tuber diameter was significantly and positively correlated with tuber fresh weight. Tuber fresh weight showed a positive correlation with tuber dry weight (Table 5).

 

Table 5: Pair wise correlation coefficients for nine quantitative traits of 36 yam genotypes evaluated at Jimma, 2015

Traits	LL	LW	PL	VL	NVPH	TL	TDi	TFW	TDW
LL	1.00	0.771**	0.475**	0.154	-0.369*	0.453**	0.359*	0.185	0.101
LW		1.00	0.452**	0.053	-0.197	0.347*	0.446**	0.288	0.270
PL			1.00	-0.027	-0.42**	0.295	0.352*	0.145	0.021
VL				1.00	0.419**	0.735**	0.182	0.307	0.419**
NVPH					1.00	0.067	-0.215	0.026	0.142
TL						1.00	0.338*	0.353*	0.266
TDi							1.00	0.454**	0.288
TFW								1.00	0.653**
TDW									1.00

*p < 0.05, ** p < 0.01

LL= Leaf length (cm), LW= Leaf width (cm), PL=Petiole length (cm), VL= Vine length (cm), NVPH= Number of vine hill^-1, TL= Tuber length (cm), TuDi= Tuber diameter (cm), TFW= Tuber fresh weight (t/ha) and TDW= Tuber dry weight (t/ha).

  

Table 6: Spearman’s rank correlation coefficients showing pair-wise association of qualitative traits assessed among 36 yams landraces

Traits	LC	LS	Las	PC	VC	TwDr
LC	1.00	0.013	-0.118	0.485**	-0.148	0.118
LS		1.00	-0.132	-0.389**	0.028	0.109
Las			1.00	-0.032	0.268	0.001
PC				1.00	-0.025	-0.077
VC					1.00	0.115
TwDr						1.00

**Significant difference at 0.01 probability level.

LC= leaf color, LS= leaf shape, LaS= leaf apex shape, PC=petiole color, VC=vine color, TwDr= twining direction

 

Table 7: Factor loadings for nine morphological traits of 36 yam landraces showing the most important principal components (PCs)

Traits	Factor loading
	PC-I	PC-II	PC-III	PC-IV	PC-V
LL	-0.234	0.102	0.079	0.134	0.746
LW	0.108	-0.070	-0.120	0.122	-0.962
PL	-0.261	- 0.224	0.036	0.927	0.140
VL	0.387	0.231	-0.201	0.014	-0.208
NVPH	-0.934	-0.165	-0.033	-0.268	0.163
TL	-0.017	0.040	-0.078	0.154	0.081
TuDi	-0.196	-0.269	-0.223	0.023	0.163
TFW	0.032	-0.143	1.217	-0.037	0.166
TDW	-0.173	-1.243	0.148	-0.245	-0.105
Variation (%)	11.6	11.5	11.4	11.3	11.1
Cumulative variation (%)	11.6	23.1	34.5	45.8	56.9

LL= Leaf length (cm), LW= Leaf width (cm), PL=Petiole length (cm), VL= Vine length (cm), NVPH= Number of vine hill^-1, TL= Tuber length (cm), TuDi= Tuber diameter (cm), TFW= Tuber fresh weight (t/ha) and TDW= Tuber dry weight (t/ha).

 

Correlation of six agronomically important qualitative traits was analyzed using the Spearman’s rank correlation procedure (Table 6). Leaf color was positively correlated with leaf shape and twining direction. Leaf shape showed a significant (P < 0.001) and negative correlation with the petiole color. The leaf apex shape was negatively correlated with petiole color. Petiole color was negatively correlated with vine color and twining direction (Table 6).

 

Principal component analysis:

A total of nine quantitative traits data was used for principal component analysis (PCA), which revealed that the five most important PCs contributed 11.6%, 11.50% 11.4%, 11.3% and 11.1% of the total variation, respectively (Table 7). Number of vine per hill, tuber dry weight and tuber fresh weight were the traits that contributed most to the variation in the first three PCs. Petiole length was contributed more to the variation in the forth PC, whereas, leaf length and leaf width were the largest contributors to the variation observed in the fifth PC.

 

Cluster Analysis:

The quantitative trait was analyzed using agglomerative hierarchical clustering to construct a dendrogram (Figure 1). Three major clusters were formed among the yam landraces from southwest Ethiopia. Cluster I was composed of 14 landraces and was further subdivided into two sub clusters, Ia and Ib. The sub cluster Ia was the landraces 59/02 (1), 56/76 (6) and 0001/07 (32) were genetically similar and collected from the same area of Jimma but distantly related to other accessions in the same sub cluster Ib. In sub cluster II, entries formed two sub-sub clusters. The landraces 34/87 (29) was closely related to 7/85 (35), 58/02 (22) and 116 (10). Cluster III consisted of 17 landraces and was categorized into sub clusters IIIe and IIIf.  Sub cluster IIIe was further divided into two groups where 10/002 (18), 24/02 (25), 39/87 (23) and 32/83 (24) were similar and formed a group. The landraces in sub cluster IIIf formed two groups, where 07/03 (14), 45/03(15) and 37/87 (17) were closely related. The most unique landraces identified were 59/02 (1), 7/85 (35), 3/87 (5) and 60/87 (27). Based on the cluster analysis (Figure 1), landraces 16 (27/02), 30(21/02), 20 (06/2000) and 2(68/02) were the most diverse.

 

Table 9: Frequency distribution (%) and Shannon diversity index of 10 qualitative traits for 36 yam landraces

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 shape	Ovate	13.89	0.86
		Chordate	66.67
		Sagittate	19.44
6	Leaf apex shape	Obtuse	33.33	0.63
		Acute	66.67
7	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
8	Petiole wing color	Green	16.67	0.90
		Green with purple edge	63.89
		Purple	19.44
9	Twinge direction	Clockwise	94.44	0.21
		Anticlockwise	5.56
10	Vine color	Green	41.67	0.68
		Light green	58.33

 

Figure 1: Dendrogram of 36 yam landraces based on quantitative data for morphological traits constructed using agglomerative hierarchical clustering. Note: see Table 2 for codes of landraces numbers

 

Frequency distribution and Shannon–Weaver diversity index of yam landraces based on Qualitative traits:

Frequencies of landraces for various qualitative traits are presented in Table 9. From the total 61.11% of the landraces were dark green leaf colors, where as 58.33% of the test landrace were light green vine color. About 66.67% of the landraces were acute leaf apex shape (Table 9). The Shannon–Weaver diversity index was calculated to indicate the level of diversity among the landraces under investigation. Index values range between 0 and 4.6 using the natural log (versus log₁₀). A value near 0 indicated that every species in the sample are the same and vice versa (Hennink and Zevan, 1991). In this study the Shannon–Weaver index values ranged from 0.21 for twinge direction to 1.64 for petiole color (Table 9). Therefore, the tested landraces showed considerable variation for petiole color.

 

DISCUSSION:

Storage tuber yield is a complex trait that interacts with many important contributing factors. Improving some of the yield components contributes to yield improvement. It is important for researchers to think the association among the pairs of the yield-related traits, thus correlation studies are essential for assessing the association among the traits. In the present study, significant correlations were observed among the storage tuber yield and related traits. The landraces with traits that are highly significant and have low coefficients of variation can be used as selection criteria for improvement. Information on significant correlation among the characters is important for initiation of breeding programmes as it provides an opportunity for selection of desirable landraces with desirable traits simultaneously. Various studies have reported correlations among yield and yield components. According to Mulualem and Dagne, (2013) reported a positive and highly significant correlation between tuber diameter and storage tuber yield and a positive significant correlation between tuber length and tuber fresh weight. Moreover, a non-significant negative correlation was observed between number of vine hill^-1 and tuber diameter. Alem et al. (2014) reported a significant positive correlation between vine length, number of female flowers per plant and number of branches per plant was important yield components influencing storage TFW in yam. In their study, the authors indicated that yield components were positively correlated with each other. Monkola (2013) also observed significant correlations among the tuber yield per plant with and plant height of cassava. Further, Tsegaye et al. (2006) reported storage tuber length and dry matter contents are the best characters to select Ethiopian sweet potato landraces. In other studies tuber yield per hill was also reported to have a positive significant correlation with vine length, tuber length and number of verticals per hill. Tuber yield was also found to be positively correlated with plant height, vine length, tuber length and number of tubers per hill (Kifle, 2006, Abebe, 2008).

 

High variation was observed among the quantitative and qualitative traits measured in this study. Variation in qualitative traits was also observed and reported in taro accessions by Paul et. al, (2013). Loko et al. (2015) reported variation on the qualitative and quantitative traits and identified specific traits as new sources in Guinea yam landraces. The traits included, vine length, tuber length, leaf length and petiole length.  Mulualem. (2013) further reported highly significant differences among the quantitative traits in aerial yams and the qualitative diversity index values ranged from 14% for tuber shape to 38% for leaf color. Loko et al. (2015) further reported the presence of genetic diversity among the yam accessions of collected from Benin using agro morphological traits. Knowledge of patterns of diversity of genetic material is of great importance and is a key component in crop improvement and breeding (Dominic et al. 2014).

 

Characterization of yam landraces based on agro morphological traits had great contribution for better assessment of the genotypes and identification of best genotypes with desired characteristics for breeding (Abebe, 2008). Based on the dendrogram, the landrace collections from one area were placed in almost all of the clusters and were mixed in terms of the provincial origin. This shows the presence of genetic diversity among the landraces within and among the regions. The results in this study concur with the study of Mulualem and Weldemichel, (2013) where the authors reported genetic diversity among the aerial yam landraces, and the clustering of landraces was not based on the areas of collections. This shows the presence of genetic diversity among the landraces within and among the Southwest region of Ethiopia. It may also be due to gene flow from neighboring districts and sharing of storage tuber by farmers amongst themselves (Loko et al. 2013). Moreover, farmers share storage tuber and name the same landraces differently in various districts (Tamiru, 2006). Farmers’ practices may also influence the handling and conservation of the genetic material on their fields. The presence of vast diversity among the landraces in this study was clearly shown by the distant relationships among the landraces. The diverse landraces could be useful for selection in plant breeding programmes and for further genetic improvement (Loko et al. 2013). They can also serve as potential parents for hybridization to get desirable segregants. The presence of genetic diversity in the genetic pool allows breeders to make selections of the distantly related genotypes based on the phenotypic traits of interest, more especially the traits that may be attractive to researchers, farmers and end-users (Alina et al. 2017).

 

CONCLUSIONS:

Evaluation of landraces based on phenotypic traits can be useful for characterization, conservation and maintenance of genetic resources. This study revealed the five most important principal components among the yam landraces evaluated at Jimma. Traits that were highly significant and positive correlations were observed among the yield related traits and could be selected for strategic improvement in breeding programs. There was morphological diversity among the yam landraces studied and the landraces 16 (27/02), 30(21/02), 20 (06/2000) and 2(68/02) were identified as the most diverse. The phenotypic diversity based on quantitative and qualitative traits is crucial for plant genetic resource conservation, characterization and identification and for strategic selection and isolation of novel genes based on specific traits. The best landraces with desired quantitative and qualitative traits were 27/02, 68/01, 08/02, 6/02, 10/002 and 24/02 identified in this study. These landraces have highest mean tuber length, tuber fresh weight and tuber dry weight. The landraces can be selected for further breeding and conservation.

 

ACKNOWLEDGMENT:

Ethiopian Institute of Agricultural Research (EIAR) and Jimma Agricultural Research Center (JARC), are acknowledged for financial and technical support of this study.

 

REFERENCES:

1.      Abebe W. 2008. Morphological and molecular characterization of cultivated Guinea yam accessions and their wild Relatives (Dioscorea cayenensis Lam.complex) from south and southwest Ethiopia. Ph.D. thesis, Addis Ababa University. Ethiopia.

2.      Abebe W, Demissew S, Fay MF, Smith RJ, Nordal I, Wilkin P (2013) Genetic diversity and population structure of Guinea yams (Dioscorea spp.) and their wild relatives in South and Southwest Ethiopia as revealed by microsatellite markers. Genet Res Crop Evol 60: 529–541.

3.      Alam S, Euphemia S, Bora P, Saud BK.2014.  Genetic variation in different cultivars of greater yam (Dioscorea alata). Journal of root crops, 40(1): 1-5.

4.      Alina M M, Hussein A Shimelis and Mark D. 2017. Agro morphological diversity of South African sorghum genotypes assessed through quantitative and qualitative phenotypic traits. South African Journal of plant and soil, 1-10

5.      Atnafua Bekele, 2014. Studies on molecular genetic diversity and useful genomic traits of yam Dioscorea spp.) germplasm collections from Ethiopia. Ph.D. thesis, Addis Ababa University. Ethiopia.

6.      Coursey, D.G. 1976. Yams. In Simmonds NW (ed.) Evolution of crop plants, first edition. Longman Group limited, UK.

7.      Dansi, A, Mignouna, H.D, Asiedu, R. and Quin, F.M. 1999. Morphological diversity, cultivar groups and possible descent in the cultivated yams (Dioscorea cayenensis /D. rotundata complex) in Benin Republic. Genetic Resource and Crop Evolution, 46: 371-388.

8.      Dansi, A, Barry, H.and Vodouhè, R. 2013. Production constraints and farmers’ cultivar preference criteria of cultivated yams (Dioscorea cayenensis Dioscorea rotundata complex) in Togo.International Journal of Biology, 4:191-199.

9.      Dominic AO., Ukaobasi E, Ogon T. 2014. Association and path coefficients analysis of fresh root yield of high and low cyanide cassava (Manihot esculenta Crantz) genotypes in the humid tropics. Journal of Crop Science and Biotechnology,17(2): 103-109

10.   FAO. 2005. FAOSTAT database. Food and Agriculture Organization, Roma, Italy. www.fao.org

11.   Firew M.2007. Infra-specific folk taxonomy in sorghum (Sorghum bicolor (L.) Moench) in Ethiopia: folk nomenclature, classification, and criteria. Journal of Ethnobiology and Ethnomedicine, 3(38):1-18.

12.   Genres.2008. Genres statistical software User’s Guide Version 16, Genres Inc. USA.

13.   Hennink, S. and Zeven, A.C. 1991.  The interpretation of Nei and Shannon-Weaver within population variation indices, Euphytica, 51: 235-240.

14.   Hildebrand, E.A, Demissew Sebsebe and Wilkin, P. 2002. Local and regional landrace disappearance in species of Dioscorea L. (Yams) in Southwest Ethiopia. Proceeding of the 7^thinternational congress of ethno biology. University of Georgia press, pp.717.

15.   IPGRI/IITA. 1999. Descriptors for yam (Dioscorea spp.). International Institute for Tropical Agriculture, Ibadan, Nigeria / International Plant Genetic Resources Institute, Rome, Italy, p.66.

16.   Jackson JE. 1991. A user’s guide to principal components. New York: John Wiley and Sons.

17.   KifleA.2006. Characterization and divergence analysis of some Ethiopian taro [Colocasia esculenta (L.)] accessions   M.Sc. Thesis, Haramaya University, Haramaya, Ethiopia, p.84.

18.   Loko Y. L., Dansi A, Linsoussi C., Assogba P, Dansi M., Vodouhè R, Akoegninou A. and Sanni A. 2013.Current status and spatial analysis of Guinea yam (Dioscorea cayenensis Lam. -D. rotundata Poir. complex) diversity in Benin. International Research Journal of Agricultural Science and Soil Science, 3(7): 219-238.

19.   Loko Y. L., Adjatin A., Dansi A., Vodouhe R.and Sanni A. 2015. Participatory evaluation of Guinea yam (Dioscorea cayenensis Lam.–D. rotundata Poir. complex) landraces from Benin and agro-morphological characterization of cultivars tolerant to drought, high soil moisture and chips storage insects. Genet Resour Crop Evol, (2015) 62:1181–1192

20.   Miege, J. and Demissew Sebsibe. 1997. Dioscoreaca. In: Edwards Demissew S., Hedberg S, I (eds.)  Flora of Ethiopia and Eriteria, Vol  6, Hydrocharitance to Aracea. The national herbarium, Addis Abeba, Ethiopia/The department of systematic botany, Uppsala, Sweden.

21.   Monkola M. 2013. Genetic variability and association among yield and yield related traits in cassava (Manihot esculenta Crantz) in Southwest Ethiopia. MSc. Thesis, Jimma University, Ethiopia.

22.   Mulualem T, Dagne Y.2013.Studies on correlation and path analysis for root yield and related traits of Cassava (Manihote sculenta Crantz) in South Ethiopia. Journal of Plant Sciences,1(3):33-38.

23.   Mulualem T, Weldemichel G. 2013. Agronomical evaluation of aerial yam (Dioscorea bulbifera) accessions collected from South and Southwest Ethiopia. Greener Journal of Agricultural Sciences, 3(9): 693-704.  

24.   Mulualem T 2013. Genetic diversity of Aerial yam [Dioscorea bulbifera (L.)] accessions in Ethiopia based on agronomic traits. J. Agriculture, Forestry and Fisheries, 2(2): 67-72.

25.   Mulualem, T., 2016. Genetic diversity, path coefficient analysis, classification and evaluation of yams (Dioscorea spp.) in southwest Ethiopia. Ph.D. Thesis, Haramaya University. Ethiopia

26.   Paul KK., Bari MA, Debnath SC.  2013. Correlation and path coefficient studies of yield and yield attributing characters in taro [Colocasia esculenta (L.)]. Journal of Bangladesh Academy of Sciences, 37(2): 131-137

27.   SAS Institute. 2000. Statistical Analytical Systems SAS / STAT user’s guide version 8(2) cary NC: SAS institute inc.

28.   Tamiru M. 2006. Assessing diversity in yam (Dioscorea spp.) from Ethiopia based on     morphology, AFLP marker and tuber quality, and farmers’ management of landraces. Ph.D. Thesis, George August University, Germany.

29.   Tamiru M., Heiko, C, Becker, B.and Maass, L. 2011. Comparative analysis of morphological and farmers’ cognitive diversity inyam landraces (Dioscorea spp.) from Southern Ethiopia.Tropical Agriculture Development, 55(1):28–43.

30.   Terauchi, R, Chikaleke, V, Thottappilly, A. and Hahn, S.K. 1992. Origin and phylogeny of Guinea yams as revealed by RFLP analysis of chloroplast DNA and nuclear ribosomal DNA.Theor. Appl. Genet. 83:743-751.

31.   Tsegaye E, Devakara FV, Nigussie D. 2006. Correlation and path analysis in sweet potato and their implication for clonal selection. Journal of Agronomy, 5(3):391-395.

32.   Vavilov, N.I. 1951. The origin, variation, immunity and breeding of cultivated plants. Chronica Botanica Company, Waltham, Massachusetts, U.S.A.

 

 

 

Received on 18.01.2021         Modified on 02.02.2021

Accepted on 14.02.2021  ©AandV Publications All right reserved