MSc

Watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] is a popular dessert
vegetable of the Cucurbitaceae family. Even though the demand for fruit is very high,
watermelon production confines to a limited area of 100 hectares with a production of
840 metric tonnes in Kerala. Precision farming is gaining importance in vegetable
production and fertigation is an integral part of it. Watermelon responds well to
fertigation in terms of growth and yield enhancement at different stages of crop like
establishment phase, vegetative phase, flower initiation and at the time of harvesting.
Erratic rainfall is the main limiting factor for watermelon cultivation in southern
Kerala. Chitosan as a bio stimulant has a potential role in improving yield, quality,
biotic and abiotic stress resistance of agricultural crops which can be exploited in the
production of watermelon also. Researchers reported that bio stimulant effect of
chitosan on plants was not much clear and it might be due to the increased
photosynthetic rate by its application. Hence the present study was undertaken with an
objective to standardise fertigation and to evaluate the effect of chitosan on
biochemical and morphological characters of triploid seedless watermelon hybrid,
Shonima from December 2021 to March 2022 at the Department of Vegetable
Science.
The experiment was conducted in split plot design with four levels of fertigation
(50 % RDF, 75 % RDF, 100 % RDF and 125 % RDF) in main plots and three chitosan
concentrations as foliar application (0.1 %, 0.2 % and 0.3 %) in subplots. Control was
maintained with a level of fertilizer application @ 70: 25: 25 kg NPK/ha (KAU POP)
and without any foliar application of chitosan. Fertigation was scheduled at three days
interval and foliar application of chitosan was done at the pre flowering and fruit
setting stages. Weather parameters like maximum temperature, minimum temperature,
relative humidity and rainfall were recorded. As the crop duration during the summer
season was shortened from 120 days to 90 days, only 25 splits of fertigation (6, 12, 7
during establishment, vegetative and fruiting stages respectively) were completed out
of 40 (6, 12, 22 during establishment, vegetative and fruiting stages respectively).
Fertigation doses given were 21.87: 15.62: 37.5 kg NPK/ha (50% RDF), 32.81: 23.44:
56.25 kg NPK/ha (75 % RDF), 43.75: 31.25: 75 kg NPK/ha (100% RDF) and 54.68:
39.06: 93.75 kg NPK/ha (125 % RDF).
Fertigation levels significantly influenced vegetative and floral characters of
watermelon. Longest vine length (3.87m) was recorded by 125% RDF. Male flower
anthesis (24.39 days) was found to be early in 50 % RDF. Fruit and yield characters
along with quality parameters were significantly influenced by fertigation doses.
100% RDF recorded maximum equatorial diameter (16.90 cm), polar diameter (17.55
cm), fruits/plant (4.52), average fruit weight (1.61 kg), yield/plant (5.97 kg/plant) and
lycopene content (5.76 mg/100g). Maximum TSS (8.64°Brix) was recorded in 75 %
RDF and maximum total sugar (5.38%) in 50 % RDF which was on par with 75 %
and 100 % RDF. Chitosan concentrations influenced fruit, yield and quality
parameters of watermelon. Foliar application of 0.1 % chitosan recorded maximum
fruit equatorial diameter (16.76 cm), polar diameter (17.43 cm), fruits/plant (4.25),
average fruit weight (1.94 kg), yield/plant (6.23 kg/plant), TSS (8.87 °Brix), lycopene
content (4.96 mg/100g), reducing sugar (3.54 %) and total sugar content (5.38 %).
50% RDF recorded lowest rind thickness (1.17 cm). Interaction effect of fertigation
doses and chitosan concentrations on fruit and yield characters and quality parameters
was found to be significant. Treatment combination of 100 % RDF + 0.1 % chitosan
spray recorded maximum equatorial diameter (18.08 cm), polar diameter (18.87 cm),
average fruit weight (2.38 kg), yield/plant (8.06 kg/plant) and lycopene content (6.72
mg/100g). Maximum TSS (9.46 °Brix) and reducing sugar (3.98 %) was recorded by
75 % RDF + 0.1 % chitosan spray. Maximum total sugar content (5.67 %) was
observed by 50 % RDF + 0.1 % chitosan spray. BC ratio (2.01) was found to be
maximum with 100 % RDF + 0.1 % chitosan. Soil nutrient status was increased after
the crop duration. Vulnerability index of watermelon bud necrosis virus, percentage
disease index (PDI) of fusarium wilt and gummy stem blight reduced after foliar
application of chitosan.
The crop duration was reduced during the summer season hence, the
recommended dose of fertigation for Shonima (90 days duration) was 43.75: 31.25: 75
kg NPK/ha. The recommended chitosan concentration was 0.1 % and treatment
combination 100 % RDF + 0.1 % chitosan was found to the best for yield and quality
parameters of watermelon.
Fertigation enhanced the nutrient uptake thereby improved the growth, yield and
quality of watermelon. Chitosan having potential role in biotic stress tolerance by
regulating the jasmonic acid responsible for this by generating hydrogen peroxide.
Enhanced yield and quality of fruits with foliar application of chitosan could be
studied further with reference to physiological aspects like photosynthetic rate,
stomatal conductance, transpiration rate etc. Biochemical and morphological traits of
seedless watermelon was improved with influence of fertigation and foliar application
of chitosan compared to conventional method of fertilizer application without any
foliar spray of chitosan.