Sesame ( Sesamum indicum
L.) is a crop of great antiquity and probably one of the oldest oilseeds under cultivation. No records on sesame outdate those of Babylon in Sumeria where it was known in 2350 B.C. At present the crop is grown in many tropical and subtropical countries, among which India, China, Mexico, the Sudan and Venezuela rank first in production. Since 1967 most published research has been carried out in India and Venezuela.
The total world production which varies considorably from year to year, has shown since 1950/1951 no consistent trend of increase or decrease. It amounted to about 1.8 million ton both in 1950/1951 and 1969/1970. Approximately 10 per cent of the production moves into international trade. In Nigeria purchases of sesame seed by the Marketing Board arrived at 17,459 ton in 1969/1970 and 5,714 ton in 1970/1971. The export is mainly directed towards Italy. Sesame seed contains about 50 Per cent oil and 20 per cent protein, it is a popular constituent of various local dishes and is highly regarded because of the good quality of its oil.
The crop is well established in parts of four province- of the Northern States of Nigeria. The production areas are characterised by their location between latitudes 6° and 10°, a duration of the dry season of about 4 to 5 months, an annual rainfall of about 1,000-1,500 mm, a vegetation of rather open savannah woodland and a top soil of loamy sand. The cultivation and crop handling follow traditional patterns and the use of machinery is uncommon.
Most of the experimental work reported here has been carried out at the Agricultural Research Station, Mokwa, Nigeria. Section 4 deals with spacing and density experiments. Ways of sowing vary in the different production areas of Nigeria but basically two methods can be distinguished. (a) The Igbirra method, characterised by sowing on ridges about 4 m apart at a spacing of 45 cm between the stands and with about 16 plants per stand, and (b) the Tiv method, which involves broadcasting,
rarely followed by thinning; plant counts per unit area showed considerable variation, the mean plant density value being calculated as 673,000 plants per ha. In view of soil and water conservation, sowing on ridges has been a recommended practice in Nigeria for a long time, the distance between the ridges usually being 91 cm. The experimental results under such conditions were interpreted as to give an optimum for a spacing of about 6 cm. on the ridges. Sowing on the flat in 1971 produced a maximum-yield at a spacing of about 22 x 13 cm. In this case a formula derived from Bleasdale and Nelder (1960) was found to describe well the relation between spacing and yield.
In both methods, described under (a) and (b) there is room for improvement.
In Nigeria. it is common experience that for a good number of crops early sowing, immediately after the onset of the rains, results in maximum yields and delay of sowing causes yield reduction. Factors thought to affect sowing date differences and their consequences for crop growth and yield, were, daylength changes, leaching of nitrogen, capping of the soil caused by hard rain, saturation of the soil with water, and differences in light intensity, disease and post incidence and temperature during the growing season.
The data in section 5 provide a quantitative evaluation of the effect of sowing date on growth and yield of sesame. They indicate that the first four factors mentioned cannot explain the typical "sowing date delay effect." However, changes in light intensity, disease incidence and possibly temperature during the season influence the relation between sowing date and crop growth.
Most of the common sesame cultivars are characterised by opening or dehiscent capsules. This capsule character has the advantage that it simplifies threshing, but the disadvantage that it increases seed loss. The discovery in 1943 of the indehiscence character in Venezuela by Langham was of great significance, as it enabled increased mechanisation of sesame production, and was expected to reduce seed loss. However, the results of experiments described in section 6 showed that losses caused by shattering of seed from opening capsules is less than visually estimated, and that seed loss need not exceed 2 per cent if a good harvesting method is applied (Fence B). It is concluded that the character of indehiscent capsules will become of value only when combines can be employed economically at harvest. Picking or stripping of capsules appeared to be a method of no practical value.
Section 7 mentions the main diseases and pests of sesame and deals in more detail with a virus, disease called leaf-curl. Attempts to transmit the disease with plant sap and with seed failed but white flies were observed to act as vectors of leaf-curl. The damage caused by the disease can be disastrous and it embodies an actual or potential threat to sesame cultivation in Nigeria. Sowing date trials showed that delay of sowing after the onset of the rains increases infection and that the disease incidence decreases when sowing is postponed till after the middle of July. Sowing after the middle of August results in disease-free crops. The magnitude of the white fly population, as estimated by counts on yellow, sticky traps, was not always a reliable indicator for the extent of disease infection. Resistance to leaf-curl was correlated with hairiness in an F 4
bulk population, but occurred also in glabrous plants and reduced the disease damage considerably.