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Ethnobotanical Leaflets 13: 1288-94. 2009. Influence of Metolachlor on Physiological Growth
Character of Tomato (Lycopersicon
esculentum L.) *B. U.Olayinka1, K. S. Olorunmaye2
and E. O. Etejere2 1 Biology Department, Kwara State College of
Education (Technical), P. M. B. 0001 Lafiagi, Nigeria 2 Department of Plant Biology, P.M.B.1515, University
of Ilorin, Ilorin, Nigeria *E-mail: umarbolaji@yahaoo.com Issued
01 October 2009 Abstract A field trial was carried out to
investigate the effects of various concentrations (0, 1, 2, 3kg.a.i/ha) of
metolachlor on physiological growth character of tomato. Results of this study showed that
weeds were decreased in proportion to applied concentration of metolachlor.
Metolachlor at 3kga.i/ha did not improve physiological growth character of
tomato in spite of effective weed reduction.
Tomato leaf area ratio (LAR) declination with age was higher in the
plots sprayed with metolachlor at 1-2kg.a.i /ha than those obtained in the
weedy control plots. The relative
growth rate (RGR) and net assimilation rate (NAR) of tomato in the weedy
control plots were adversely affected as from 6th week after transplanting
.This period coincides with high weed
density. However, the relative growth rate (RGR) and net assimilation
rate (NAR) of tomato in plots sprayed with metholachlor at 1-2kg.a.i/ha
showed vigorous growth till 7th week
after transplanting(WAT) before showing declination. These results suggest
that metolachlor at 1-2kg.a.i/ha could be an effective and safe herbicide for
application in transplanted tomato. Key words: Tomato, Lycopersicon esculentum, weed, metolachlor. Introduction Tomato, Lycopersicon esculentum L., is an important vegetable crop with
edible fruit commonly grown in the tropics. It has a variety of uses such as
serving as condiments for stew baking of bread as well as sources of vitamins
A and C (Ayodele, 1976). It can also be processed into canned tomato soup,
sauce and paste (Atherton and Rudich, 1986). Weed interference has been
reported to exert a considerable influence on tomato growth. Weaver and Tan
(1983) reported that weed interference decreased tomato yield and this
reduction in yield was apparent if weeds were allowed to remain in the crop
longer than 25 days after transplanting.
Akobundu (1987) observed that weeding frequency is high in tomato
production. This is because the plant does not develop crop canopy that
effectively shades the ground at any stage in its life cycle. Most popular
method of weed control in this crop throughout the tropics is manual weeding.
This is because the process is simple and the farm size is small (Akobundu,
1987). However, hand weeding becomes obviously tedious where large acreage is cultivated. Usoroh (1988) observed
that in reducing drudgery normally associated with manual weeding and yield
loss due to weed competition, chemical weed control via herbicides become
imperative to enable the crop to attain its growth potential. In arable crop setting many growth rate
studies have been carried out to evaluate the performance of various test
crops. Adelana (1976) used net
assimilation rate (NAR), crop growth rate (CGR) and relative growth rate
(RGR) to determine the growth rate of tomatoes under staked and unstaked
control treatments. Also, Adeyemi (1999) used leaf area index (LAR), leaf
area ratio (LAR) and relative growth rate (RGR) to evaluate the growth rate
of cacao seedlings under different weed control treatments. This study was designed to investigate
the growth rate of tomato under selective soil applied herbicide metolachlor
using weed flora present on the field of study. It is expected that knowledge
of growth rate under chemical weed control treatment can be an important and
helpful guide in determining the herbicide concentration that will be
effective in weed control and safe for tomato. Materials and
Methods Seeds of Lycopersicon esculentum
(var.Roma) were obtained from seed
unit of Kwara Agricultural
Development Project (KWADP) in
August 2000. The seeds were spread on
a tray to identify and remove foreign particles. Thereafter, the seeds were
packed in paper envelope and stored at room temperature (24-27OC)
until they were used for the study. Experimental
layout Field experiment was conducted on sandy
soil at Shao, Kwara State (80 311N, 40 411E)
between themonths of September and December, 2000. A plot size of 7m by 6m2 was
used. The plot consisted of 4 rows
having sub plots, each size of 3m2 with approximately 0.3m in
between row spacing. These subplots were of randomised block design where
treatments were allotted randomly with five replicates. Spraying
Technique Three different levels of 1, 2, and
3kg.a.i/ha of metolachlor and no herbicide treatment control were studied.
The various herbicide concentrations were sprayed using knapsack sprayer
using time volume method. Field plating Tomato seedlings of uniform size
previously raised in the nursery were transplanted on the field when
they were three- week-old, at spacing 0.6m
between and within the subplot of 3m2thus producig twelve
seedlings of tomato per subplot vo. Metolachlor was applied as
pre-transplanting with knapsack of 20litres capacity, calibrated to deliver a
spray lume o f 166L/ha following procedure explained in the spraying
technique. No weeding was carried out in the weedy control plot, i.e 0kg/ha,
thereby subjecting the seedlings in this treatment to weedy condition
throughout the period of the investigation. Diseases and pests were
controlled by treating the seeds with Apron Plus 50SD (10%metalaxy,
6%carboxin and 34%furothiocarb) at the rate of 2.5g/500gseeds). The field was
fertilized with NPK 20-10-10 applied at the rate of 60kg/ha three weeks after
transplanting. Each sub plot was
manually irrigated with 20 litres of water at three day intervals
throughout the dry season to maintain
normal crop growth. Weed count (density) was carried out
using 0.5x 0.5m2 quadrat. All weeds rooted within 0.25m2
quadrat position adjacent to the crop plant were taken at weekly interval for
weed density estimation. Five tomato plants were harvested at soil level for
above ground dry matter determination at weekly interval over nine weeks
period per treatment .Tomato leaves, stems and fruit were harvested and oven
dried at 80oC to constant weight. Leaf area was determined using
graphical method. Growth analysis of tomato plants was
estimated from the primary data of leaf area and dry matter accumulation
using various formulae for growth analysis. Leaf area ratio was calculated using the method of
Adeyemi, (1999), and Abayomi and Adedoyin (2004) as, LAR =Leaf area/Shoot dry weight Relative growth rate was estimated as, RGR =LogeW1-logeW2/t2-t
While net assimilation rate (NAR) was estimated
using the formula of Evan (1972), Abayomi
and Adedoyin (2004) as, NAR= (W2-W1)(logel2-logeL1)/(L2-L1)(t2-t1) Where W1 is the initial and W2
is the final (dry) weights of the plant shoot; L1 and L2 are the
leaf area at t1 and t2; t1 and t2 are time
interval at which the observation were made. Results and Discussion Weed density The results of this study have shown that there was low weed infestation about (130.4n/m2) with low number of weeds emerging per unit area (Figure 1). This could be due to severe drought condition during the period of the experiment which delayed weed emergence and initial tomato growth (LNRB 2000). The number of weeds emerging per unit area in transplanted tomato field was reduced in proportion to the applied concentration of the herbicide sprayed plots compared with weedy control plots (Figure 1). Most effective weed control was given by metolachlor at 2-3kg/ha (Akobundu1987, Kristen et al. 2004). Considering the weed species that were encountered in this study, Panicum laxum, Rhychelytrum repens and Tridax procumbens were effectively controlled by metolachlor 2-3kg.a.i./ha. However, the herbicide is less effective against Imperata cylindrical, Sesamum alatum and seedling of Hymnocardia acida even at higher dose of 3kg.a.i/ha.
Figure 1: Effect of soil applied
metolachlor on weed density in tomato (Lycopersicon
esculentum). Growth analysis Leaf area ratio (LAR) generally declined
with age of tomato plants after each rate attained its maximum peak (Figure
2).The decrease in leaf area ratio observed could be due to continuous
increase in plant biomass without a corresponding increase in leaf area
coupled with senescence and death of old leaves. This trend was observed to
be lower in the weedy control plots or plots sprayed with metolachlor at
3kg.a.i/ha compared with plots sprayed with metolachlor at 1- 2kg.a.i/ha. A
reduction in LAR with age has been observed as a feature in annual plants
(Higgs and James 1969). Adelana (1976)
and Adeyemi (1999) have reported similar observation in their studies of
tomato (Lycopersicon esculentum )
and cocoa seedlings (Theobroma cacao)
respectively. The relative growth rate and net assimilation rate (Figures 3 and 4) after each rate attained their respective peak followed trend similar to leaf area ratio. This further suggests that growth and development of tomato either gross or net of tomato plants under weedy control plots were adversely affected by weed infestation as from 6th week after transplanting when the weed interference was high. The increase in growth rate with age under the plots sprayed with metolachlor at 1-2kg.a.i/ha till 7th week after transplanting was because tomato plant is still showing vigorous growth when the leaf area and dry matter were still increasing as the plant size increases. The declination in RGR with age could be attributed to the fall in leaf area ratio and net assimilation rate. Thus the yield per unit area showed a decrease with age after each rate attained its peak. The declination in NAR could be due to reduction in photosynthetic activity of the leaves as they become senescent and died. The findings were consistent with the results of studies carried out on T. cacao by Adeyemi (1999). It could therefore be concluded from this study that metolachlor at 1-2kg/ha could be considered effective and safe herbacide for application in tomato plots.
Figure 2: Effect of soil applied metolachlor
on leaf area ratio of tomato (Lycopersicon
esculentum).
Figure 3: Effect of soil applied
metolachlor on relative growth rate of tomato (Lycopersicon esculentum).
Figure 4: Effect of soil applied
metolachlor on net assimilation rate of tomato (Lycopersicon esculentum). References Abayomi, Y. A. and Adedoyin, G. A. 2004. Effect of planting date and fertilizer
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