Evaluating Performance of Sesame (Sesamum indicum L.) Genotypes in Different Growing Seasons in Northern Ethiopia

Ethiopia is one of the famous and major producers of sesame in sub-Saharan Africa, and Ethiopian sesame is among the highest quality in the world. +e experiment was conducted in Northern Ethiopia for three growing seasons (2013–2015) under a rain fed condition with the objective of identifying high-yielding genotypes and their agronomic traits. +e experiment consisted of twelve genotypes laid down in randomized complete block design with three replications. +e genotype, year, and genotype × year interaction components showed statistically highly significant variation (p< 0.001) for most of the agronomic traits which clearly confirms the presence of genotype × year interaction in this study. +e highest combined mean grain yield (906.3 kg/ha) was obtained from Hirhir followed by Serkamo white (756.5 kg/ha), and from the three growing seasons, the highest grain yield (1161.5 kg/ha) was recorded from Hirhir grown in the second growing season (2014). +e growing seasons were different from one another in allowing the genotypes to have a different performance, and all of the agronomic traits, except thousand seed weight, were statistically different across the three growing seasons. In the ordination of the genotypes and agronomic traits, PCA1, which accounted for 38.3% of the variation, was positively associated with grain yield, branches per plant, length of the pod-bearing zone, plant height, number of pods per plant, number of seeds per pod, and thousand seed weight. On the contrary, PCA2, which accounted for 19.7% of the variation, was positively associated with days to 50% flowering and days to 50% maturity.


Introduction
Sesame (Sesamum indicum L.), locally called "Selit" or "Simsim," is one of the major economically important oil crops in Ethiopia. e sesame sector is millions of dollars industry that supports the livelihoods of thousands of small farmers and hundreds of medium-to-large-scale private farms along with thousands of other actors involved in the chain of production-to-consumption/export continuum. Ethiopia is one of the famous and major producers of sesame in sub-Saharan Africa, and Ethiopian sesame is among the highest quality in the world; especially seeds produced in the Humera and Gondar regions are renowned worldwide for their high quality (color, taste, and nutty aroma) [1]. From nutrition point of view, sesame is also rich in phosphorous, iron, magnesium, manganese, zinc, and vitamin B 1 [2]. mainly in low-and mid-altitude areas, altitudes between 500 and 1300 meters above the sea level (masl) being the most suitable. Sesame productivity can go up to 1200 kg/ha and up to 2100 kg/ha at rain fed and irrigation production conditions [6]. However, the productivity of the available sesame varieties released so far (both for rain fed and irrigation production) is lower than some of the producing countries. Hence, the objective of this study is to evaluate di erent available genotypes which may be indispensably important for further sesame breeding and to identify high-yielding genotypes with desirable agronomic traits.

Materials and Methods
e experiment was conducted in Northern Ethiopia, Western zone of Tigray, speci cally in the Humera area for three growing seasons (2013)(2014)(2015). e agroecology of the locations is described as hot to warm semiarid plain (SA1-1) with edaphic and climatic variations as indicated in Table 1 and Figure 2, respectively.
Further description of the genotypes is given in Table 2. e experiment was laid down in randomized complete block design (RCBD) having three replications in both of the cropping seasons. Each genotype was randomly assigned and sown in a plot area of 2.8 m by 5 m with 1 m between plots and 1.5 m between blocks keeping inter-and intrarow spacing of 0.4 m and 0.1 m, in that order. Each experimental plot was treated equally as per the recommendations of the crop for the growing area.

Data Collection.
Each treatment was laid down in a total plot area of 10 m 2 area (5 meter row length having 5 number of rows at 0.4 m interrow spacing) and net plot area of 6 m 2 . From the net plot area, seven plants were selected randomly and tagged to collect the agronomic traits data (except grain yield) and the average values of the agronomic traits from the seven plants were considered for further statistical analysis. Grain yield of the genotypes was taken from the net plot area (6 m 2 ) of the three replications, and the average yield was taken and converted in to yield per hectare. e detailed explanation of the agronomic traits collected from this study and analyzed for further interpretation is elucidated below:

Variance Estimation of the Agronomic Traits.
e results of the agronomic traits obtained from the combined analysis of variance of the genotypes are illustrated in Table 3. e genotype, year, and genotype by year interaction (G × Y) variances were decomposed to provide a general overview in relation to the evaluated traits and overall performance of the genotypes ( Table 3). As a result, the genotype, year, and genotype × year interaction components showed statistically highly significant variation (p < 0.001) for most of the agronomic traits. However, thousand seed weight (in gram) (TSW) was not statistically significant across years, and length of the pod-bearing zone (LPBZ) was not statistically significant in the genotype by year interaction (G × Y). is statistical difference was due to both of the main and interaction effects of the genotypes and the years. As indicated in Table 3, the genotypes were clearly different in their agronomic traits, and similarly the years, in which the experiment was conducted, were different mainly in the rainfall received during that specific growing season (Figure 2). Moreover, Table 3 clearly shows that the response of the genotypes were unstable and fluctuated in their trait expression with change in the growing seasons. ese all observable facts clearly confirm the presence of genotype by year interaction (G × Y) in this study. [7] also reported Table 2: Genotypic code, status, and source of the evaluated sesame genotypes.

Genotype
Genotype code Status Seed color Source of seed   International Journal of Agronomy similar differences of the genotype, year, and genotype × year interaction effects in sesame genotypes.

Agronomic Traits Performance of the Evaluated Sesame
Genotypes. Combined analysis of the 12 sesame genotypes evaluated in three different growing seasons is depicted in Table 4. e result of the combined analysis showed that the genotypes were significantly different in their grain yield across the three different growing seasons showing that the genotypes were unstable in their grain yield. In addition to this, the grain yield analysis showed that there was a statistically significant difference among the genotypes in all of the agronomic traits and the genotypes were unstable, even all of the other agronomic traits. Similarly, the grand mean across years was significantly different, and the growing seasons were also not stable. e highest grain yield (906.3 kg/ha) was obtained from Hirhir (local check), which is a local cultivar, followed by Serkamo white (756.5 kg/ha). is is because of the genetic difference between the sesame genotypes, and because of this, farmers' cultivar is well adapted to the growing environments (both the location and the years) [8]. Also, a significant difference of sesame genotypes in their grain yields evaluated in different growing seasons is reported. Almost all of the newly evaluated advanced lines which were expected to be better than the farmers' cultivar were beaten by the farmers' cultivar in terms of grain yield. Furthermore, Hirhir was also the early maturing genotype (which matured at 86.56) although it was as early maturing as some genotypes like Acc-051-02-sel-1-(2), Acc-202-374, and NN-038. Genotype Tate was better in its number of branches per plant (3.4 branches per plant) although it was statistically at par with the local cultivar Hirhir (3.1 branches per plant). Similar to this study, there was a significant difference in grain yield, number of branches per plant, and days to maturity among the evaluated sesame genotypes [7,9]. Regarding to plant height, the highest stature (136.4 cm) was recorded from genotype Acc-051-02-sel-14 although it was statistically at par with other seven genotypes (Table 4). In terms of the pods per plant (PPP), the highest number of pods per plant (35.16 PPP) was recorded from the local cultivar Hirhir. However, it was statistically nonsignificant with Acc-051-02-sel-1-(2), Acc-051-02-sel11--(1), Acc-051-02-sel-14, Acc-202-374, Cross22XT-85(24-2), NN-038, and Tate ( Table 4). Number of pods per plant is among the most important agronomic traits in sesame, so since most of the evaluated sesame genotypes were equally important in their pods per plant, most of these genotypes are important for further sesame breeding. Generally, since there are some genotypes which are statistically nonsignificant with the best farmers' cultivar in some of the major agronomic traits, the genotypes should be maintained for further sesame breeding program.

Performance of the Sesame Genotypes across the ree
Years. Performance of the sesame genotypes in terms of their agronomic traits evaluated in three different growing seasons is depicted in Table 5. e growing seasons were different from one another in allowing the genotypes to have different performance [7]. e agronomic traits of sesame genotypes were different in different growing seasons [10]. Most of the agronomic traits, except thousand seed weight, were statistically different across the three growing seasons Table 5. [1] also found a significant difference of different agronomic traits of wheat evaluated across years. ere is a possibility for occurrence of such variation of genotypes in their agronomic traits across years and even across locations, and this may be both a challenge and an opportunity for plant breeding and breeders [11]. e highest grain yield of the sesame genotypes was recorded in the second growing season (2014).
is might be because there was optimum and evenly distributed rainfall during this growing season (Table 5). On the contrary, the highest number of branches per plant, length of the pod-bearing zone, plant height, and number of pods per plant were recorded in the first growing season (2014). e combined performance of the different agronomic traits of the sesame genotypes is depicted in Table 4. However, Table 6 is organized to clearly visualize the performance of the different agronomic traits of the sesame genotypes evaluated in the three growing years. From the three growing seasons, the highest grain yield (1161.5 kg/ha) was recorded from the local cultivar Hirhir grown in the second growing season (2014). Similarly, the highest length of the pod-bearing zone (81.8 cm) and plant stature (170.3 cm) was recorded from the local cultivar Hirhir grown in the first growing season (2013). In terms of the number PPP and number of SPP, the highest PPP (41 PPP) and the highest SPP (64.7 SPP) were obtained from Acc-202-374 grown in 2013 and Hirhir grown in 2014 growing season, respectively (Table 6).    International Journal of Agronomy

Ordination of the Sesame Genotypes and eir Agronomic
Traits. To clearly visualize the association of the sesame genotypes and their agronomic traits, a biplot is depicted in Figure 3. In the ordination of the genotypes and their agronomic traits, the first two principal components (PC s ) accounted for 58% of the total variance (38.3% and 19.7% for PC1 and PC2, respectively) ( Figure 3). A bi-plot was used by [12] to visualize the associations of different parametric and nonparametric stability measures in faba bean. e importance and relationship between variables within a component are determined by the magnitude and direction of factor loadings within a PC [13]. e sign of the loading indicates the direction of the relationship between the components and the agronomic traits. Principal component axis one (PCA1) that accounted for 38.3% of the variation was positively associated with grain yield, branches per plant, length of the pod-bearing zone, plant height, number of pods per plant, number of seeds pod, and thousand seed weight. In contrast to this, PCA1 was negatively associated with days to 50% flowering and 50% maturity. [14] also found a similar result to this finding. In contrast to this, PCA1 was negatively associated with days to 50% flowering and 50% maturity (Figure 3). [11,14] also found similar results to this finding from their study on sesame genotypes.
In any plant breeding program, the final objective is to boost quality and/or quantity of a required crop. Knowing the association between the required trait and other related traits is a prerequisite for such programs. Yield is a dependable complex inherited character as a result of interaction of several contributing factors that may be related or unrelated. Hence, it is paramount important to see the association of the sesame genotypes and their agronomic traits and the association of the different agronomic traits among each other. Hence, according to Figure 3, days to 50% flowering (DF) and days to 50% maturity (DF) were negatively associated with most of the agronomic traits like thousand seed weight (TSW), grain yield (Yield), length of the pod-bearing zone (LPBZ), plant height (PH), pods per plant (PPP), and seeds per pod (SPP). G9 (Hirhir) was positively and highly associated with the first principal component (PCA1) as well as with the agronomic traits like yield, pods per plant, and length of the pod-bearing zone.

Conclusion and Recommendation
e genotype, year, and genotype × year interaction components showed statistically highly significant variation (p < 0.001) for most of the agronomic traits of the sesame genotypes which confirm the presence of genotype by year interaction (G × Y) in this study.
Regarding the grain yield, the highest grain yield (906.3 kg/ ha) was obtained from Hirhir followed by Serkamo white (756.5 kg/ha). Generally, since there are some genotypes which are statistically nonsignificant with the best Hirhir in some of the major agronomic traits, the genotypes should be maintained for further sesame breeding program. On the contrary, the highest grain yield of the genotypes was recorded in the second growing season (2014), and the highest grain yield (1161.5 kg/ha) was recorded from the local cultivar Hirhir.
Principal component axis one (PCA1) that accounted for 38.3% of the variation was positively associated with grain yield, branches per plant, length of the pod-bearing zone, plant height, number of pods per plant, number of seeds pod, and thousand seed weight. On the contrary, the second component axis (PCA2) which accounted for 19.7% of the variation was positively associated with days to 50% flowering and days to 50% maturity.
Finally, this study is of paramount importance to identify the best genotypes in terms of the different agronomic traits and to investigate the agronomic performance of sesame genotypes across different growing seasons, and this study also forwards for sesame researchers to carry out different researches across locations and across years.
Data Availability e supplementary material file includes data used for the analysis of this manuscript.

Conflicts of Interest
e authors declare that they have no conflicts of interest.

Supplementary Materials
e abbreviations and the words they stand for listed below: DF, days to 50% flowering; DM, days to 50% maturity; BPP, number of branches per plant; PH, plant height (cm); PPP, pods per plant; SPP, seeds per pod; LPBZ, length of the podbearing zone (cm); TSW, thousand seed weight (gram). e experiment was conducted for three years in Humera in a randomized complete block design with three replications. 12 advanced lines which come from previous selections were used in the experiment, and these advanced lines were tested for three years. All of the yielded and other agronomic traits were collected from the 12 advanced lines conducted for three years. (Supplementary Materials)