Plant Materials The experiment was carried out at the plant physiology laboratory and green house of the Faculty of Bioresources and Food Industry, Universiti Sultan Zainal Abidin, Besut Campus, 22200 Besut, Terengganu, Malaysia. Yellow flesh watermelon (Citrullus lanatus (Thunb) Matsum and Nakai) seeds were purchased from Bumi Maju Agro, an authorized seed dealer of Terengganu and used for germination and growth and developmental study. The mixture of cocopeat and soil as the growing media were prepared in the germination tray. The mixture of cocopeat and BRIS soil were prepared and added in 16 × 16 inches poly bags for the planting of watermelon seeds.
Seed Sowing and treatment application The germination trays were prepared by filling the holes with growing media mixture of cocopeat and soil. Then, the growing media was moistened with water prior to sowing the watermelon seeds to provide moisture to the media. After that, each hole of the tray was sown with one seed only. All the planted seeds in the tray were placed in the germinator. The seeds were treated with five different temperatures including control (normal temperature 250), 200, 300, 350 and 400. All the seeds were treated with different temperature regimes only two days. After treatment application all the seedlings were kept at normal condition. The growing media regularly moistened by applying water to ensure saturation throughout the germination period.
Transplanting in polybags After 3 weeks, all the seedlings were transplanted into the poly bags containing the planting media which are the mixture of coco peat and BRIS soil with ratio 1:1. Each poly bag contained about 1 kg of growing media. The growing media in the germination tray was sprayed with water to make it easy to pull out the seedling from the tray. A small hole was dug at the center of the poly bag. After that, the seedlings were transplanted in the 16 × 16 inches poly bags. Each poly bag contained one seedling only.
Measurement of seedlings growth and developmental characteristics Seeds were considered to have germinated once the radicle had protruded at least 2 mm from the testa. The days of required to seed germinate, and its germination rate were recorded. The vine length, number of leaf and leaf area were measured weekly. The root development was measured after seedling already uprooted from the polybags. The length of root was measured by using ruler. The whole seedling was taken out from the poly bag. Fresh weight of the seedlings was taken by weighing the plants by using weighing balance. Then, the plants were dried in oven at 600 for 24 hours and its dry weight was taken.
Determination of chlorophyll and pigments content Chlorophyll content was measured by using SPAD-502 meter (Minolta Japan) according to the method described by Saifuddin et al. (2009). This SPAD meter was lightweight, hand-held device that widely used for accurate, fast and non-destructive measurement of leaf chlorophyll content by means of absorbance or transmittance measurements. The measurement was taken by meter which was simply clamped over leafy tissue. The meter showed the indexed chlorophyll content reading. Carotenoid content was measured by using spectrophotometer. This measurement was taken to measure the photosynthetic pigments of leaf. The leaves samples were collected for each treated seedling. Then, the samples were cleaned and air dried. The veins of the leaf were removed, and the leaf was cut into small pieces. Samples were weighed about 1 g by using electronic balance for each treatment. The weighed samples were crushed by using mortar and pestle and were homogenized in 10 ml of 80% acetone for each 0.25 g samples. Then, the homogenate was filtered through mounted in glass funnel. The filtrate was poured into 3 mL cuvette and its absorbance was measured in wavelengths of 663 nm, 645 nm and 480 nm wavelengths for measurement of chlorophyll a, chlorophyll b and carotenoid, respectively. The readings were taken by spectrophotometer devices. The concentrations of chlorophyll and carotenoids were calculated by using the formula of Arnon (1949).
Stomatal conductance, chlorophyll fluorescence and photosynthetic yield and leaf Total Soluble Solid (TSS) A Portable Leaf Porometer, Model SC-1 was used to measure the stomatal conductance (CID Bio-science, USA). Measurement was taken for three replicates at different spot of a single leaf. The average of all three replicates was calculated and the results were recorded. Chlorophyll fluorescence was measured by using JUNIOR-PAM Chlorophyll Fluorometer. The JUNIOR-PAM was controlled by PC through USB interface. The fluorometer requires no external power supply as it is powered by the PC via the USB line. WinControl-3 software was installed, and PC was connected to JUNIOR-PAM through USB. The magnet was clamped to the leaf, and then the chlorophyll fluorescence readings were measured and saved in the PC. Initial fluorescence (F0), maximal fluorescence (Fm) and photosynthetic yield (Fv/ Fm) were obtained. Then, variable fluorescence (Fv) was calculated. The TSS of leaf was measured by using handheld refractometer. The leaf sample was crushed by using the pestle and mortar and the juice was extract. Then, 1 to 2 drops of the leaf extract were placed onto the sensor of hand refractometer. The TSS readings were recorded as described by Khandaker et al. (2012).
Statistical Analysis The experiment was arranged under a Completely Randomized Design (CRD) with five (5) replications. The data were analyzed by using SPSS statistical software. The one-way ANOVA was applied to evaluate significant differences in the parameter studied for the different treatments. Differences at p < 0.05 were considered as significant.