Evaluation of Orange Flesh Sweet Potato Varieties ( Ipomoea batatas L.) in West Hararghe Zone of Oromia Region, Eastern Ethiopia

: Sweet potato is an important food security root crop in west Hararghe. it is mainly important for pregnant women and children particularly the Orange fleshed type, which produces storage-carotene, roots precursor of rich in Vitamin A. Therefore, Orange fleshed sweet potato is a promising variety to address the Vitamin A deficiency needs of women and children and to prevent malnutrition in study areas. This experiment was undertaken at Daro labu and Habro districts during 2016-2017 cropping season. The objective of the research was to identify high yielding, adaptable and disease tolerant variety to the study area. A total of three improved Orange fleshed sweet potato varieties; Beletech, Kulfo, Tulla and one local check were used as experimental materials. The experiment was arranged in a Randomized Complete Block Design (RCBD) with three replications. The analysis of variance revealed that there was a significant difference (p<0.05) among the varieties for growth, yield and yield related trait. The highest mean value of marketable root yield was recorded from Kulfo variety with (15.2 ton ha -1 ) and 0.55 ton yield advantage than a local check. During the experimental period, there was low rainfall distribution in west Hararghe, particularly in the study site. Within the existing moisture stress, Kulfo variety was performed well and gave higher root yielder than improved and local check at both locations. In addition to this, the stability analysis result shows that variety Kulfo was the most stable variety across the two sites. Likewise, the yield and yield contributing parameters and stability analysis over location are important selection parameters which can serve as indicators of adaptability of the sweet potato to the study area and can also be utilized for improving in root yield of sweet potato. Therefore, Kulfo variety was selected as high yield in, adaptable and stress tolerant variety under the rainfed condition at Daro labu and Habro districts of West Hararghe.


Introduction
Orange fleshed sweet potato (Ipomoea batatas L.) is a dicotyledonous plant belonging to the family Convolvulaceae [1]. It can be grown in tropical, subtropical and frost-free temperate climatic conditions. It is among very valuable root crops in Ethiopia and it is widely grown in the eastern, southern and south western parts of the country [2,3]. The roots are used as a staple food while the vines and leaves are used as animal feed. Orange-fleshed sweet potato varietiesare m carotene. Increasing the consumption of orange-fleshed sweet potato at the household level can increase supplementation of the diet with vitamin A [4]. Most of the orange-fleshed sweet potato varieties contain-13000 of carotene β to16000 µg and this100 contributes g -1 retinol to activity equivalents (RAE) [5]. Therefore, according to [5], the addition of 100g OFSP in a daily diet can prevent VAD in children and significantly reduce the death of mothers. [6] also indicated that a 100 g OFSP can-carotene, provide which is equivalent more to more than10006500 µg RAE.
In Ethiopia, sweet potato has been cultivated for many years and is important in a diet where population growth is highest and landholding is the least [7]. Over 95% of the crop is produced in the Southwestern, Eastern and Southern parts Hararghe Zone of Oromia Region, Eastern Ethiopia where it has remained for centuries as one of the major subsistence crops especially in the periods of drought [8]. The most widely grown sweet potato varieties are white-fleshed, with negligible amounts of beta carotene and this could be contributing to vitamin A deficiency [9]. Vitamin A Deficiency (VAD) is widespread and has severe consequences for young children in developing countries [10] including Ethiopia. Although the yield and beta carotene content of white-fleshed sweet potato varieties are low [11] in many countries including Ethiopia, there is a high potential for increasing both the yield and beta carotene content through the use of improved Orange Fleshed Sweet Potato (OFSP) varieties. The OFSP varieties are rich in beta carotene that the body uses to produce vitamin A [11] OFSP varieties are a cheap and year-round source of vitamin A [9] to the poor families in developing countries of East Africa such as Ethiopia because OFSP is well accepted by young children [10] and can combat VAD.
In West Hararghe, availability of the Orange flesh Sweet potato varieties are not evaluated to adaptability. Therefore, evaluation of adaptability for these Orange flesh Sweet potato varieties is important into the study zone to solve food security problem at the same time to combat Vitamin A Deficiency. Therefore, the objective of this experiment was to identify promising and adaptable orange-fleshed sweet potato variety in terms of yield and yield contributing parameters, disease tolerant and hence could combat Vitamin A Deficiency (VAD) at a community level in the tropics of east Ethiopia, at West Hararghe zone.

Description of the Study Area
The experiment was conducted at two locations Daro labu (on station), and Habro districts (Balbaleti PA), under rainfed condition during the 2016-2017 main cropping season. Mechara Agriculture Research Center is located between 8° 34' N latitude and 40 20' E longitudes. The altitude of the area is about 1760 m. a. s. l. It has a warm climate with annual mean maximum and minimum temperature is 31.8°C and 14°C, respectively. The mean annual rainfall is 1100 mm. The soil of the experimental site is well-drained slightly acidic Nitosol. Habro district was located at 404 km east of Addis Ababa, the capital city of Ethiopia and 75 km South of Chiro, West Hararghe Zone town. Its place is located at 8° 51' N and 40° 39' E and an altitude of the district ranges between 1600 -2400 m. a. s. l. The mean maximum and minimum temperatures are 20°C and 16°C, respectively. The district receives an annual average rainfall of 650 mm to 1000 mm. Black sandy and loam soil types are the most dominant soil of Habro District.

Experimental Design and Treatments
Three Orange flesh sweet potato Varieties (Beletech, Kulfo and Tulla), were brought from Hawasa agricultural research center and evaluated with one local check. The experiment was laid out in Randomized Complete Block Design (RCBD) and replicated three times. The plot was 3m x 3m = 9m 2 area and each plots consisting of four rows, which accommodated ten plants per row and thus 40 plants per plot. The spacing between plots and blocks was 1 m and 1.5 m, respectively.

Land Preparation and Planting
The experimental land was ploughed, harrowed, ridged was prepared before planting. Vine cuttings of 30 cm length with six nodes were prepared from the healthy stem of each OFSP. Cuttings were planted on the ridges [12] with about three nodes buried in the soil uniformly for all treatments at the spacing of 70 cm between rows and 30 cm between plants [13]. Weeding, Earthing up and other cultural practices were done according to the standard recommendation for Sweet potato uniformly for all varieties.

Data Collected
Data were recorded on five plants randomly selected from the inner rows of each experimental plot and expressed on per plant basis for each trait under study. The mean of four plants was used for statistical analysis. The following data were recorded: average number of vine per plant, vine length (cm), average root number per plant, root diameter (cm), root length (cm), marketable root yield (ton ha -1 ), unmarketable root yield (ton ha -1 ), and total root yield (ton ha -1 ).

Data Analysis
All collected data were subjected to analysis of variance, for each of the locations and then combined, using SAS software version 9.1. Means that differed significantly were separated using the LSD procedures. Stability of the varieties, the interaction of varieties and environments were analyzed by the GGE Biplot Model.

Mean Performance of Varieties-Growth Traits
The combined analysis of variance across two locations showed significant (P<0.05) difference among the tested sweet potato varieties for growth traits (vine length and vine number per plant ( Table 3). The highest mean value of vine length (103.4cm) and vine number per plant (5) was recorded from Tulla variety (Table 3), whereas the lowest vine length (90.00 cm) and vine number per plant (4.58) were recorded from local check and Beletech variety, respectively ( Table 3). The variation in vine length of sweet potato varieties at a different location may be due to a response of the genetic characteristics of the varieties to growing environmental factors. The present study is more or less in agreement with the findings of [14] the vine length ranged from 93.3 to 488.7 cm. Moreover, the results of this study are corroborated by the observation of [15] that genetic and environmental factors play a vital role in the root development process. This result is consistent with that of [16] who showed that the number of stems per plant is influenced by variety. This might be attributed to genetic differences, which in turn influenced the number of sprouts or eyes on the cutting. In addition, the highest brunch number (13.66) is recorded from accession 4411329.

Yield and Yield Related Component
Root Length: Significant variation was observed among the varieties for root length at Habro, while non significant (P<0.05) at Mechara and over locations. Local check had the highest root length (15.66 cm) followed by Beletech variety (12.77). The results are in agreement with the findings of [17] reported that the variety of Daulatpuri produced the highest root length (14.44 cm).
Root diameter: The root diameter was non-significant at two location Daro labu and Habro districts, while significance (P<0.05) difference at two sites over location ( Table 3). The maximum root diameter (7.33cm) was from Kulfo variety at Habro district, whereas the lowest root diameter (4.3cm) was from Beletech variety was observed at Mechara on station.
There are genetic as well as environmental factors that cause a difference in the size of roots.
Root diameter, non significance difference between varieties, even though, the highest mean root diameter (6.6cm) was obtained from Kulfo variety at over two locations ( Table  3). The difference observed in root diameter among the OFSP varieties is attributed to their genotypic difference. The current result is in conformity with the finding of [18], who conclude that sweet potato variety, H19/06 gave significantly the highest root diameter (6.92 cm) compared to the other varieties included in their study. Similarly, [19] reported that the highest root diameter (4.9cm) was recorded from Tulla variety than local and Beletech varieties.

Root Number per Plant, Marketable and Unmarketable Yield
The varieties significantly differed in root number per plant and marketable root yield, while significantly differed on unmarketable yield at both locations ( Table 3). The highest mean value of root number per plant, (6.67) and marketable yield (15.2 t/ha) was recorded from Kulfo variety at two combined over location. The results were significantly difference due to the different variety of oranges fleshed sweet potato. These results are closely related to those reported by [18] the number of root per plant which varied from 1.73 to 6.03. [20] also found the number of roots per plant varied from 4.70 to 11.76. The differences in roots yield could be attributed to genetic variations among genotypes in partitioning photosynthesis. Similarly, [19] reported that the highest mean root length was obtained from Tulla variety than Beletech Kulfo and local varieties.
Differences in yield due to the genetic makeup among genotypes have also been reported in other sweet potato trials [21] as well as other crops such as common beans (Phaseolus vulgaris) [22]. Moreover, [3] also reported significant variation between sweet potato genotypes in yield and other desirable traits in their adaptation trial in different agro-ecologies of Ethiopia. Similarly, the differences in marketable root yield could be attributed to the genetic variations among the OFSP varieties in partitioning photosynthesis [21]. Based on the current result we can suggest that variety Kulfo was the best variety for marketing purposes but the two newly introduced OFSP varieties Beletech and Tulla were considered the poorest varieties for marketing purposes [9]. Thus, these are important parameters for selection and serve as indicators of adaptability of the crop to the study area. Accordingly, a variety of Tulla can be used as a good source of marketable roots where production is aimed at marketable roots [13].  Unmarketable root yield: Unmarketable root yield was none significantly (p<0.05) different among the Orange flesh sweet potato varieties (Table 3). Similarly, [19,13] also observed none significant differences in unmarketable root yield among sweet potato varieties in their study. Even though unmarketable root yield was none significantly different among the orange flesh sweet potato varieties, the highest unmarketable root yield (0.89 ton/ha) was recorded from local check at over location in two sites. On the other hand, the lowest unmarketable root yield (0.31t/ ha) was recorded in (variety Beletech) which is also not significantly different from two varieties ( Table 3). [23] had observed wide variation among sweet potato varieties in most of the parameters (number of branches per plant, vine length, fresh fodder weight, and saleable root yield) studied and attributed such differences to genetic composition.

Total Root Yield (t/Ha)
Total root yield Significant (p<0.05) difference occurred in total root yield among the orange flesh sweet potato varieties evaluated ( Table 2). The highest total root yield (15.54 ton ha -1 ) was recorded in Kulfo variety (Table 3). However, the lowest total root yield (10.64 ton ha -1 ) was recorded in Variety Tulla. The differences in total root yield could be attributed to varietal differences among the orange flesh sweet potato varieties [24].

Stability Analysis Across Environment
The GGE-biplot analysis showed that Kulfo variety had relatively higher Principal component one (PC1) values, indicating that this variety had the highest average fresh root yield (Figure 1). Tula variety was low yielding but most stable and Beletech was low yielding and least stable. From the result of the relationship among test environments (figure 2), the angles between the two locations: Habro and Mechara were less than 90°C and imply that they are positively correlated to one another. In addition, large positive PC1 scores for genotypes indicate that those genotypes had relatively higher mean values [25]. The average environment coordinate (AEC) is the line that passes through the bi-plot origin and separates genotypes with mean values below average and above average [26]. Those genotypes to the right of this line are high yielders, while those to the left are low yielders [3].
Since the most stable genotypes are located close to or along the zero line of IPCA ordinates [27]. Stable and high yielding traits are among the major agronomic characteristics required by farmers in sweet potato adoption as such varieties that can have both of these characteristics would likely be accepted by farmers [28,29]. Therefore, based on marketable root yield result from two locations, Kulfo varieties were good performance over other variety and standard checks (Figures 1 and 2).

Conclusion and Recommendation
Three improved varieties (Kulfo, Tulla, and Beletech) including one local check were evaluated with the objective of selecting adaptable and best performing Orange type sweet potato variety in the study area. The experiment was carried out on two districts, West Hararghe zone in 2016 and 2017 cropping season.
The current study results showed that the most important yield and yield contributing parameters: root diameter, number of roots per plant, marketable root yield and total root yield were significantly varied among the orange-fleshed sweet potato varieties evaluated. Kulfo variety was the highest marketable yield across locations while Beletech variety was consistently lowest marketable roots yielding variety. Based on over locations analysis result of marketable root yield from two locations, Kulfo variety was good yield performance over other varieties and local check. The maximum mean marketable yield of improved varieties (15.2 t/ha) in Kulfo variety and 3.75% yield advantage than the local check. in addition, this genotype had wider adaptability and stability across environments. Therefore, Kulfo variety was potential candidates that could replace local variety, an OFSP variety that is currently grown in West Hararghe zone.
Therefore, Kulfo variety was recommended as the best OFSP variety with optimum yield and highest adaptability in the Eastern part of Ethiopia and potentially combat VAD at community level. Since the findings are based on only three varieties and one check at two locations, further studies using more variety, combination of locations and seasons is required to generate more reliable information on the performance of varieties across the location.