Abstract:
This study was conducted to develop a protocol for tomato cultivation under 50% shade
conditions inside protected houses to mitigate the problems arising with high temperature, using
foliar application of Paclabutrazole (PBZ) to control plant growth while achieving optimum yield
at the Faculty of Agriculture, University of Ruhuna. There were six treatments as T1(0
ppm/control), T2(25 ppm), T3(50 ppm), T4(100 ppm), T5(200 ppm) and T6(400 ppm) following
Randomized Complete Block Design (RCBD) with five replicates. The treatments were applied 14
days’ interval as a foliar spray. The vegetative and reproductive data were recorded at 14 days’
interval. Data were statistically analyzed using ANOVA and means were separated by Dunnett’s
test at 5% probability level. The results revealed that there was a significant effect of PBZ on plant
height increment, internodal length, stem diameter and leaf area. T1/control exhibited the highest
plant height increment (136.80 cm) while T6 exhibited the lowest (76.40 cm). T1/control was
recorded the highest internodal length (4.40 cm) for both internodes and T6 was recorded lowest
(3.07 cm and 2.80 cm) for 3-4 & 7-8 nodes respectively. T1 was recorded as the highest (129 cm2
& 248.10 cm2) and T6 was the lowest leaf area values (66.84 cm2 and 94.50 cm2) for 7th & 14th leaf
respectively. The highest stem dimeter was shown in T6 (6.86 cm & 9.50 cm) while T1/control
was recorded lowest (5.38 cm &7.19 cm) at 2.5 cm and 7.5 cm above base of the stem, respectively.
The number of leaves/plant and the chlorophyll content were not significantly different. The T3,
T4, T5 and T6 were significantly lower than T1/control (131.00) on number of flowers/plant
while T4(4.40) was only significant for the number of fruits/plant with T1/control (8.00). The
T6(108.81 g) was significant compared to T1/control (215.48 g) on fruits weight. The diameter
of fruits was significantly lower in T3, T4, T5 and T6 than T1/control (3.88 cm). The T2 was not
significant with the T1/control for any reproductive parameter. The results indicate that applying
25 ppm PBZ with 14 days’ interval effectively controls plant height (25.4% reduction) without
negatively affecting yield.
