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Published in Issue No. 142, page 59 to 62 - (11236) characters
Collection and evaluation of sesame (Sesamum spp.) germplasm in NigeriaG.Akpan-Iwo A.A. Idowu S.M. Misari
Sesame belongs to the family Pedaliaceae and genus Sesamum (Hutchinson and Dalziel 1963; Purseglove 1974). The genus consists of about 36 species of which 19 species are indigenous to Africa (Weiss 1983; Uzo 1998). In Nigeria, three species, which include S. alatum (Thonn), S. indicum L. and S. radiatum Schum & Thonn, are widely cultivated for different purposes (Dabir 2000). The most popular species is S. indicum, which has hundreds of varieties and strains with considerable variation in size, form, growth pattern, colour of flowers, seed size, seed colour and composition.
Sesame is widely grown in northern and central Nigeria. The production areas are located between latitudes 7 –14°N, have a dry season which lasts about 4–5 months, an annual rainfall of about 1000–1500 mm, a vegetation of open savannah woodland and a topsoil of loamy sand (van Rheenen 1973). The major states for sesame production in Nigeria are Adamawa, FCT Abuja, Benue, Borno, Gombe, Jigawa, Kano, Katsina, Kebbi, Kogi, Nasarawa, Plateau, Taraba and Yobe.
Nigeria has a great potential for sesame production for the domestic and export markets but the yield of this valuable crop is relatively low and varies from one area to another, due to a lack of improved varieties. Based on this, the National Cereals Research Institute (NCRI), Badeggi, which has the national mandate for the genetic improvement of sesame, considered germplasm collection to be a priority project from 1997 to 2001. The assembly and evaluation of sesame germplasm will provide a diverse genetic base for sesame improvement.
The objective of this project was to collect and conserve indigenous cultivars, landraces, useful wild species of sesame from Nigeria, and cultigens from organizations outside Nigeria. In addition, these materials needed to be evaluated for selection and subsequent use in breeding programmes with the purpose of developing improved sesame varieties suited to Nigerian conditions.
Materials and methods
Germplasm collection and evaluation
In 1998, an expedition for the systematic collection of sesame cultivars and landraces was undertaken in the northern and central parts of Nigeria where sesame is known to be produced. This collection exercise was carried out in collaboration with the Agricultural Development Project (ADP) in each of the States, using extension personnel. The method of collection involved visits to farming villages and interviews with farmers. The interviewer’s questions covered the following information: local name for sesame, maturity period, growth habit and uses.
The germplasm collection was restricted to the areas between 7°and 14°N and between 5° and 13°E at an altitude of 100–400 m above sea level. The ecological zones and States from which sesame germplasm was collected are shown in Figure 1.
Requests for exchanges of germplasm materials from Columbia and Mexico through FAO and the Institute of Agricultural Research (IAR), Zaria, Nigeria, were made in 1997 and 1998, respectively. The IAR was the national curator of sesame germplasm in Nigeria until 1987, when the national mandate was transferred to the NCRI, Badeggi. Forty two accessions were transferred from IAR, while eight accessions were received through FAO. During the germplasm collection expedition within the country, 33 accessions were collected.
The germplasm materials collected were planted in the field at Badeggi for evaluation and characterization of the major morpho-botanical and agronomic characteristics. The accessions were planted in August 1999 by drilling on the flat in plots consisting of two rows of 6 m with 60 cm spacing. The plants were thinned 3 weeks after sowing and N:P:K (15:15:15) fertilizer was applied by dibbling 1 week after thinning. Single weeding was carried out 4 weeks after planting.
Genetic variability study
The extent of genetic variability shown in different structural components and yield was also investigated during the 1999 and 2000 cropping seasons at Research Station Badeggi, Niger State. The experimental design was a randomized complete block design replicated three times. Each accession was planted in a single-row plot of 6 m length with intra-row and inter-row spacings of 20 cm and 60 cm, respectively. Five plants from each accession were selected randomly and assessed for seven quantitative agronomic traits including days to 50% flowering, plant height, number of branches, number of capsules per plant, capsule length, seeds per capsule and grain yields. The genotypic and phenotypic coefficients of variability were estimated according to the formula suggested by Singh and Chaudhary (1995), and heritability (broad sense) according to Hanson et al. (1956). Phenotypic correlation was calculated according to the procedure suggested by Falconer (1960).
Results and discussion
Germplasm collection and evaluation
Overall, 83 accessions were collected. Field evaluation showed that over 80% of the accessions appeared to be resistant to lodging, while their capsules were characterized as four-loculed fruits (bicarpellate). The capsule arrangement on the axil was mostly alternate (one capsule per axil) in all the accessions except three accessions from Mexico: ‘Eva’, ‘Tetra 77’ and ‘Pachequeno’, which had multiple capsules per axil. Pubescence was common on most accessions, while shattering of seeds after physiological maturation was a common trait in all the accessions. All the indigenous cultivars and landraces showed an indeterminate growth pattern, while the few exotic cultigens from Columbia and Mexico showed a determinate growth pattern.
Genetic variability studies
The genetic variability study of the structural components revealed a wide range of variability for all characters except capsule length. The data analyzed revealed high genotypic (GCV) and phenotypic (PCV) coefficients of variability in characters such as the number of branches per plant, number of capsules, and moderate GCV and PCV, respectively, for seed yield. Since these genetic estimates (GCV, PCV) cannot provide a reliable measure of the heritable variations on their own, a heritability estimate (h2) and genetic advance (GA) were also considered (Table 1). From the results, it can be seen that all the characters have high heritability except for capsule length. The observed high heritability along with high genetic advance (expressed as percentage of mean) indicates the most effective condition for selection in the number of branches and capsules per plant and in seed yields. This condition appears to be due to additive gene action. The observed high estimate of heritability with low genetic advance (GA) in characters such as days to 50% flowering, plant height and number of seeds per capsule tends to be influenced by non-additive genes (dominance), and selection would be slow.
The correlation coefficients for all possible comparisons of the structural components with grain yield are presented in Table 2. Seed yield was strongly and positively correlated with the number of days to 50% flowering at both the genotypic and phenotypic level. Positive genotypic correlation with seed yield was also observed in number of seeds per capsule; and the number of capsules per plant.
Plant height and number of branches correlated significantly with yield at the phenotypic level only. However, seed yield showed negative correlation with capsule length. These results on correlation agreed with the previous reports of Pathak and Dixit (1992) for black-seeded sesame. A positive association of yield with the number of capsules was also reported by Varisai and Stephen (1964) and Gupta and Gupta (1977).
Generally the study indicated that sufficient variability exists in most of the components under study. These evaluations have shown useful genetic variation in important production traits of sesame germplasm from Nigeria and other sources. The high heritability and genetic advance obtained for number of branches, capsules per plant and seed yield demonstrates the possibility of improvement through selection. These findings will enhance selection and subsequent breeding work towards the development of improved and adaptable sesame varieties in Nigeria.
The authors wish to express their profound gratitude to the Project Managers of Agricultural Development Projects (ADPs) for their cooperation towards the successful collection of the germplasm in their domains. The authors also appreciate the support of the Director, NCRI, , Badeggi, for financing the project and granting permission to publish this work.
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