The Adoption of Temperate Selected Sesame Accessions in the Tropics : Selected for Japan and Grown in Ghana

Sesame is an oilseed crop which can be grown on marginal lands. Selection of stable sesame cultivars that can adapt to local environmental conditions can be a very important food security strategy. A set of 21 high yielding sesame accessions that have been selected for a temperate region were grown in the transitional zone of Ghana during the major season of 2014. The seeds were sown after the first rain in the year in a completely randomized design, with three replications. The objective was to evaluate the effect of the contrasting environment on sesame phenology and to select cultivars with yield potential that can be accepted into local farming systems in the new environment. Morphological, physiological and agronomic traits, leading to yield were recorded in this study. Number of capsules per plant had the strongest association (72%) with seed yield. Five accessions showed a combination of early maturity < 12 weeks with high overall mean seed yield (> 20 g per plant) and good harvest index (0.29). Based on their mean performance these cultivars have been selected as promising exotic cultivars for the new locality.

Despite the improved potential for increasing the production and productivity of sesame, there are a number of challenges. Over seven million hectares were grown worldwide in 2010, which produced about four million tons of seeds (FAO, 2012). The average world yield is still low at 0.52 ton ha -1 (FAO, 2012) which is from low-yielding dehiscent varieties with poor harvest index values, and have significant yield loss during threshing (Ashri, 1998;Uzun & Cagirgam, 2006). Among these production constraints, the most crucial include the lack of improved cultivars which are high yielding, non-dehiscent and also reliable seed supply (Pham et al., 2010;Tiwari et al., 2011). The average grain yield per hectare has been reported to be relatively low in most producing countries; between 300-350 kg/ha (Phillip, 1977;Saha & Bhargava, 1980;Schilling & Cattan, 1991). The fruit capsules dehisce along the suture lines and release the seeds to the ground. These wild characters prevent mechanized harvesting and the expansion of sesame cultivation (Uzun et al., 2003). However, non-dehiscent sesame varieties with yield potential of over 1 ton ha -1 and suitable for mechanical harvest have been developed in the last decade (Langham et al., 2008) confirming the status of sesame as a viable cash crop with tremendous export potential (Oplinger et al., 1990).
Sesame is however catching attention because breeding programs for about 80 years has seen a breakthrough (Anwar et al., 2012) where the crop's major drawback, brittle seed capsules has been solved. The main reason for this delayed success in breeding programs was that it is mainly produced in developing countries and usually by smallholders (Ashri, 2007). For now collections of improved sesame species and cultivars are available in the USA, India, Russia, China, Kenya, South Korea and to a lesser extent Japan, and these provide a valuable gene pool. Ashri (2007) has indicated that, introduced sesame varieties can adapt to new environments within 2-3 seasons of replant. Cultivars to be adopted should be selected based on the local climate, resistance to local pests, and intended use (Sheahan, 2014). Although there is ample evidence indicating that sesame yield depends on the interaction of different climatic parameters such as solar radiation, temperature and humidity (Beech, 1985;Nath et al., 2001) we still had the chance to grow temperate selected sesame cultivars in a tropical area to evaluate its adaptability and yield potential.

Location and Plant Materials
Twenty-one sesame accessions (Table 1) were collected from the sesame bank of University of Toyama, Japan and the pericarp size was classified as: medium, big or large with the large being the size found on bread buns were grown under field conditions after the first rain in March 2014 at Sunyani. Sunyani lies 7.3333°N, 2.3333°W in a tropical forest-savanna transitional zone with a bi-modal annual rainfall. The field experiment was carried out at the research fields of Sunyani Polytechnic, where the annual temperature fluctuates between 25 °C and 35 °C.

Experimental Procedures
The cultivars were sown in 6 m long cultivar-alternating plots which were 100 cm apart with an interplant distance of 40 cm. This was replicated in each of the three blocks. After 2 weeks of growth, plants were thinned to 2 plants per stand and data collection was initiated. Ten mid-row plants of each cultivar per block were randomly tagged as target data subjects.

Data Collection
Plant height from the base to the terminal leaves; stem height from the base to first capsule; fruiting zone length which was the height between the first basal and terminal capsules were each measured using a graduated wooden measure. The number of branches of five randomly selected tagged plants was counted. The number of capsules per plant from each of the five randomly tagged plants was taken. Plants were each cut at the base and the wet biomass yield/plant was determined (leaves, stem, capsules). Fresh capsule weight from ten plants, seed yield per plant, seeds/capsule, and 1000 seed weight were determined using an electronic balance. Harvest Index was taken as the ratio of seed yield to biomass yield per plant.

Data Analysis
Analysis of variance was carried out on above mentioned traits using 9 th edition of Genstat ® (Release 9.2, 2007). Means of treatments were separated using Least Significant Difference (LSD) after Analysis of Variance (ANOVA) in common probability levels. Note. These accessions were collected from the sesame bank of University of Toyama, Japan.
*Pericarp size was classified as: medium big or large. Large being the normal size found on commercial buns.

Results and Discussion
All the tested sesame varieties had seed colours and a ≈ 12 week maturity period which were true to type as described by the seed breeder or collector. The pericarp sizes were classified to be medium, big or large. The large seed (Table 1) is in reference to commercial seeds used in the bakery industry.
Results obtained from the 21 varieties indicate that there exist wide variations among the varieties. The distance from the first capsule down to the base of the plant was between 22-80 cm (Table 2) and was significant (p < 0.001). There was a positive correlation (65%) between the first capsule height from the base and plant height. The tallest variety (5762) measuring 149 cm and the shortest variety (603) measuring 112 cm tall had the first capsule being 63 cm and 28 cm above ground respectively. There was a significant difference (p < 0.02) among the plant heights of the varieties. Plant height had a 52% correlation with yield.
The highly branched varieties, with greater than 15 branches per plant (Table 2); as compared to the no branching types could attain a higher fruiting zone length if the branches were considered. Fruiting zone in this experiment was restricted to the main stem leading to plant height. Branching is very variable in sesame and for these varieties was significant (p < 0.001, Table 2).
Fruiting zone which for sesame is the distance between the first basal capsule and the terminal capsule was significant among the varieties (p < 0.001). The mean fruiting zone length was 87 cm. Results from these varieties indicate that fruiting zone length had a negative correlation 36% with yield. This was especially manifested in the variety (987) with a high above average fruiting zone length of 105 cm producing a seed yield of 13 g/plant. This was in contrast with some varieties e.g. (965) with seed yield 29 g/plant from a fruiting zone of 85 cm. Yield per plant as a consequent was highly significantly different (p < 0.001, Table 4).  Note. *Fruiting zone length was the height between the first basal and the terminal capsules.
There was no significant difference (p = 0.29) among the varieties in the wet biomass yield (mean = 243 g/plant) although variety (999004) which is highly branched (17/plant) had a wet biomass yield of 454 g/plant. All other forage or fresh vegetable uses of the sesame varieties were significantly different ( Table 3). The fresh capsule weight of the variety (9891), 2 g, was above the collection average of 1.4 g.
The 21 varieties had a mean harvest index/plant of 0.48 which was significant (p < 0.001). Variety (999004) also combined a low harvest index (0.29: Table 3) and a high wet biomass with good yield of 23 g/plant. Capsule numbers per plant of these varieties was the best index to predict yield (73% correlation: Table 4).  *Wet biomass yield was the fresh weight of leaves, stem and capsules on a plant. Harvest Index was taken as the ratio of seed yield to biomass yield.
The yield of any crop is a very complex quantitative character resulting from different factors, the more important of them being the yield per plant and number of plants per unit area (Menon, 1967). Although sesame has numerous varieties and ecotypes adapted to various ecological conditions (Nzikou et al., 2009;Adebowale et al., 2011) in the present study, we investigated the adaptability of temperate selected varieties in a tropical region. The tested sesame varieties had all the commercial seed colours between white and black. Seed colour is a major trait that affects consumer's acceptability. Paltak and Dixit (1992) reported that the consumer's preference for seed colour differs from region to region for which we need to confirm in Ghana. White sesame seeds, have higher oil, protein and moisture ratios as compared to black seeded sesame (Kanu, 2011). The physical appearance is a key marketing indicator and acceptability of sesame type varies greatly with cultural preferences. The Sudanese favour white seeded sesame whilst the Japanese prefer black seeded ones (Hossain et al., 2010). In particular, a larger seed size, coupled with a light-coloured seed coat like white, often command price premiums in a market-dependent manner (Cassells & Caddick, 2000;Graham et al., 2001). In parts of Asia for example, white seeded sesame sells at least 30% higher than dark coloured varieties (Chakraborty et al., 1984).  Plant density is a crucial index in sesame and an optimum of 400,000 plants/ha has been recommended (Katung, 2003). In earlier experiments in Ghana, Sintim and Yeboah Badu (2010) at 250,000 plants/ha obtained yields that were above quoted yield values in Africa. Seed yield is a complex trait governed by polygenes and therefore is influenced more by environmental factors (Basu et al., 2009). Another important factor that influences the seed yield of sesame is varietal differences hence the need to select varieties of good quality that can be adjusted to the local climatic conditions (Pham et al., 2010). In other sesame growing areas in the tropics, seed yield of 37 g per plant has been reported in controlled pollinated fields. The tested varieties with greater that 20g seed yield per plant are very promising and will be introduced into the local farming/cropping system. Although characters such as plant height of determinate varieties (Uzun & Cagirgan, 2001) and early maturation (Day, 2000;Day et al., 2002) make a great contribution to seed yield these attributes are variety specific. The most crucial index should rather relate to internode length and capsules per node. In the varieties tested, plant height and fruiting zone length were not a critical determinant of yield. Plants with tall stems should combine with short length of basal capsule from the ground, short internode and number of capsules per internode to ensure high yield. Early maturation is very important where sesame is grown as a second crop in areas with short seasons. Currently we have been able to grow sesame in a three season cycle in a year if we utilize the first rain in early March for our 12 week maturity sesame varieties. The selection of varieties should however not sacrifice plant features related to earliness for only seed yield. There have been instances where seed yield was negatively correlated with plant height (Ngala et al., 2013) which is similar to results from this experiment. In our case it was attributed to long internodes and low capsule number per node for some varieties.
Sesame has shown in other places to be highly sensitive to day length (Narayanan & Reddy, 1982;Suddihiyam et al., 1992) and has significant interactions with temperature (Suddihiyam et al., 1992). Oil content has been found to be influenced negatively by temperature (Kamal-Eldin & Appelqvist, 1994). It flowers in about 45 days under 10-hour day length. The short day length requirement was not considered to be crucial for these varieties, since summer day length is even longer in temperate regions from where the seeds were collected. Sesame is also reported to adapt to different photoperiod requirements (Ashri, 2007) as well as the existence of day-neutral cultivars. These new temperate selected varieties can fit into our cropping pattern as most of the land is normally fallow after harvesting a main crop due to the long term moisture requirements for native crops. Sesame is also known to be a good candidate when planted as a primary crop or a secondary crop after wheat (Langham et al., 2008). The performance of these adaptable varieties such as: those with more than 100 capsules per plant, 90 seeds per capsule, 4.23 g 1000-seed weight are comparable to the high yield value of 3.59 g 1000-seed weight reported elsewhere for high yielding varieties by Anwar et al. (2012) and Hassan (2012).

Conclusions
For other attributes not tested in this experiment: sesame can increase yields in subsequent cash crops by successfully improving soil moisture retention and soil texture. It is notable for its ability to grow under droughty conditions and in extreme heat and under conditions where few other crops can survive as it requires very few inputs. These attributes make sesame an excellent candidate for low-input sustainable food systems as required in Ghana.