Introduction
Vegetable sesame (Sesamum radiatum Schum), a member of the family Pedaliaceae
is an important vegetable commonly consumed in Nigeria and many other parts
of the tropics. The plant occurs throughout tropical Africa mainly as weed (Hutchinson
and Dalziel, 1963) where it is gathered in the wild and is used as a potherb.
It is one of the many neglected leafy vegetables of the tropics despite its
nutritional contribution. It is sometimes cultivated to be used as an ingredient
that increases the desirable viscosity of sauces. These sauces are mixed with
mashed food prepared from cereals or root crop flours, where it adds to the
protein, vitamin and mineral contents of the predominantly starchy diets of
the people of area concerned (Oyenuga and Fetuga, 1975;
Omidiji, 1978).
Vegetable sesame is propagated by seeds drilled in or broadcast on a wellprepared
seedbed. Seeds are at times first raised in a nursery and the seedlings are
transplanted to the wellprepared seed beds (Auwalu, 1995).
The leaves are harvested 68 weeks from seedling emergence or establishment.
The crop is harvested either by uprooting the entire plant or by repeated topping
of plants that regrow to yield harvestable branches. Nutritional analysis showed
that most tropical greens are much richer than temperate types in protein, vitamins
and minerals (Tindall, 1977; Omidiji,
1978).
Increasing the productivity of a crop like vegetable sesame requires information
on the status of the production techniques, relationship between growth and
yield parameters as well as within yield components and the degree of environmental
and fertilization influence on the expression of yield. Since yield is a quantitative
character that is a function of many related characters for an effective yield
improvement, a simultaneous improvement of most yield components is imperative.
The correlation coefficient measures the mutual association between a pair of
variables independent of other variables while regression analysis gives the
relationship between one variable and one or more factors (Ajala
et al., 1996; Babatunde and Auwalu, 2003).
The present study seeks to establish the relationship between growth parameters, yield and yield components and fertilizer application as they influence and/or determine productivity in vegetable sesame.
Materials and Methods
The experiments were conducted during the dry season of 1996 and the rainy
season of 1997 at the horticultural garden of the School of Agriculture, Abubakar
Tatari Ali Polytechnic Bauchi and the research farm of the School of Agriculture,
Abubakar Tafawa Balewa University Bauchi, Nigeria, respectively. Both research
field are approximately located at 10°17’ N, 9°49’ E and 609.3
m above sea level in the northern guinea savannah ecological zone of Nigeria
as reported by Auwalu et al. (2004).
Three levels of N fertilizer (urea = 46% N) and three levels of P fertilizer
(single super phosphate = 7.8% P_{2}O_{5}) were applied in factorial
combination laid out in a randomized complete block design with three replications
and are explicitly explained by Auwalu et al. (2004).
All the standard agronomic and cultural practices undertaken (which included
land preparation, sowing, thinning, weeds, pests and disease) with the exception
of irrigation practice in 1996, were carried out uniformly in both years.
Growth parameters such as plant height, number of leaves per plant, leaf area
index were correlated with total marketable yield t ha^{1} in 1996
and 1997 using the Pearson correlation in MINITAB 10.2 version computer software
package. The path coefficients were obtained using the correlation coefficients
used to develop simultaneous equations as described by Dewey
and Lu (1959) as follows:
In the above equations, P_{1}, P_{2} and P_{3} are
path coefficients, while r_{12} …..r _{34} are the coefficients
of correlation. The path coefficients measure the direct contribution between
yield and the concerned growth parameters, whereas the correlation coefficients
measures a mutual association between the growth parameters as explained by
Babatunde and Auwalu (2003). The direct contribution
was calculated as follows:
Where D = direct effect of iDewey
The combined contributions of two growth parameters was estimated with the
formula:
Table 1: 
Direct, indirect and total contributions of growth parameters
to total marketable yield of vegetable sesame in two years 

Where
C ij 
= 
combined effect of i and j 
r ij 
= 
coefficient of correlation between i and j 
(i and j depict direct and indirect contributions,, respectively)
The residual factors Rx which is unaccounted for by the direct and combined
contributions was estimated as follows:
Rx = 1 – (P_{1} r _{14}+P_{2}
r _{24}+P_{3} r _{34})x100 

Where
Rx 
= 
Residual effect 
Pi 
= 
Path coefficients 
r ij 
= 
Total contribution of factors i and j represented by the coefficient of
correlation in the above simultaneous equations. However, all these were
obtained through the explicit calculations presented in Table
1. The three components of direct effect, combined contribution and
residual effect should addup to unity or 100%. 
Combined analysis of variance for data on leaf fresh weight, shoot dry weight
and total marketable yield was also done. These yield components were correlated
among themselves. Similarly, regression analysis was carried out between these
yield component and the fertilizer application with the use of MINITAB 10.2
version computer software package.
Results and Discussion
In both seasons, the correlations were positive and highly significant (p<0.01).
This indicated that the growth as well as yield parameters are interrelated
among themselves. It also implies that the growth parameters are the major determinants
of vegetable sesame yield (Table 2) This result is in conformity
with the result obtained by Babatunde and Auwalu (2003)
who carried out correlation analysis between growth and yield of red variant
Roselle. It was further ascertained in this result that the taller plants possessed
higher number of leaves per plant and this eventually led to wider leaf area.
This wider leaf area would invariably lead to greater photosynthetic activity
hence, higher total marketable yield. The reason may however be attributed to
the fact that vegetable sesame is an indeterminate plant with sympodial growth
habit like pepper (Aliyu et al., undated) and Roselle (Babatunde
and Auwalu, 2003).
Similarly, the correlation coefficients of combined analysis between yield and yield components was positive and highly significant (p<0.01) as presented in Table 3. However, the highest correlation coefficient (0.952**) was obtained when total marketable yield was correlated with leaf fresh weight.
Table 4 shows that there was differential contribution of some growth parameters on total marketable yield of vegetable sesame. Plant height made the largest direct contribution of 54.02 and 34.35% in 1996 and 1997, respectively to total marketable yield. In same vein, the residual effect which cannot be accounted for by direct and combined contributions were large in both seasons. It was above half of the entire contribution (57.21%) in 1996 and up to 35.55% in 1997. Thus, it was only about 42.79 and 64.45% variation in vegetable sesame total marketable yield that could be attributed to the direct effect from plant height, number of leaves per plant and leaf area index and their combined contributions in 1n 1996 and 1997, respectively.
The result of the regression analysis between yield components and fertilization showed that both nitrogen and phosphorus fertilizer application are not very important determinant of yield (Table 5).
Table 2: 
Correlation coefficients between yield, growth parameters
and within growth as well as yield parameters of vegetable sesame in two
years 

** = p<0.01 
Table 3: 
Correlation coefficients of combined analysis between total
marketable yield and other yield parameters 

**p<0.01 
Table 4: 
Direct and combined contribution of some growth parameters
on total marketable yield of vegetable sesame presented as percentage in
two years 

Table 5: 
Combined contribution of nitrogen and phosphorus fertilization
on yield and yield components of vegetable sesame 

R^{2} = Coefficient of determination, N = Nitrogen,
P = Phosphorus 
This is evident from the fact that the coefficients of determination were infinitesimal
and not significant. In spite of nonsignificancy from the regression equation,
the total marketable yield showed negative phosphorus regression sign. This
can also be linked to the high level of residual contribution to total marketable
yield as presented in Table 4. This finding is however contrary
to that of Babatunde and Auwalu (2003) who reported
that factors (agronomic practices) were very important determinants of yield
in red variant roselle calyx.