Effect of Heat Treatment around the Fruit Set Region on Growth and Yield of Watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai]

A. Research Context

B. Knowledge Gap

C. Research Objectives

• Watermelon cultivar 'Sambok-gul'
• Watermelon sown on perlite beds in a plastic house under controlled conditions.
• Locations: Watermelon Farm, Jeongeup-Jeonbuk.
• Total of 15 plants each were randomized.
• 3 treatments:
• Control
• 14°C
• 18°C
• 3 replications.
• Spaced 45 cm and row length was 3 m wide.
• Temperature treatments were given around the fruiting region.

Data Collection and Analysis

• The data collected are:
• Length of the 1^st cotyledon to the 20^th node
• Stem thickness at the fruit set node
• Leaf length
• Leaf width
• Petiole length
• Fruit length
• Fruit width
• Leaf area
• Number of fruit set nodes
• Fresh fruit weight
• Soluble solid content
• Ca²⁺
• Mg²⁺
• Mean analysis to compare the effects of treatments using SAS software.
• The daily low temperatures prior to and after fruit set were recorded from 30 March to 21 April (Table 1).

• Stem thickness of fruit set node (8.5 mm per plant), fresh weight (1.9 kg per plant), and leaf area (355.3 cm² per plant) were observed significantly different and higher in 14°C treatment (Table 2).
• Length of 1^st cotyledon to the 20^th node (210.5 cm per plant) was found significantly higher at 18°C (Table 2).
• Increased shoot growth is considered as a parameter for the shoot demand for nutrients uptake (positive impact).
• In particular, larger leaf area (351.7 cm² per plant) was found at 18°C (Table 2).
• Larger leaf area might happen due to increase in leaf length and leaf width.
• Fresh weight was found significantly higher in temperature treatments (2 kg per plant [18°C] and 1.9 kg per plant [14°C]) than control (1.5 kg per plant).
• Temperature treatments had non-significant effect on plant height, number of fruit set nodes, and petiole length.
• Temperature treatments had significant effect on most of the growth characteristics, particularly, fresh weight, leaf area, steam thickness of fruit set node and length of the 1^st cotyledon to the 20^th node starting 15^th day after fruit set and at the time of harvest.
• The modulated temperature treatments significantly affected photosynthetic activity, increase in lateral main shoot length, growth and development of root and shoot, plant height, internode length, number of branches, flower number, leaf number, leaf area, and yield in various crops.

• 18°C treatment had significant effect on fruit length and fruit width, resulting in higher fruit weight on the 15^th day after fruit set (3 kg per plant) and harvest stage (8.3 kg per plant) (Table 3).
• Enhancement in photosynthetic productivity due to the positive effect of temperature treatments on leaf area.
• 18°C treatment had significantly higher soluble solid content (11.1%) at harvest stage (Table 3).
• 18°C treatment had significantly higher fruit set percentage (96.5%) (Figure 1).
• Imposing of temperature treatment 18°C had advantage not only in improving cultivar performance in terms of fruit weight on the 15^th day after fruit set and at harvest stage, but also the soluble solid content and fruit set percentage at harvest.
• Temperatures below or above optimum levels may influence higher differences in plant metabolic activities, fruit set, fruit quality, yield, and number of seeds per fruit.

• Temperature treatments had accelerated the accumulation of Ca²⁺ and Mg²⁺ ions with significant variations in different leaves that emerge from fruit set nodes (Table 4).
• Ca²⁺ and Mg²⁺ ions were higher in the 1^st upper leaf of the fruit set node and the 1^st lower leaf of the fruit set node, respectively at 14°C.
• Temperature treatments had higher leaf area, so promoted high photosynthetic activity and transpiration rate, and in return accelerated ion uptake rate.
• The leaf at the fruit set node is supportive source and increasing fruit size and solid soluble content during harvest stage.
• Another study:
• Higher content of Ca and Mg in the leaves at 25°C.
• Very low or high temperature may decrease various metabolic process in plant tissues, such as nutrient uptake, fluctuation in the anion exclusion volume and exchangeable Ca²⁺, chlorophyll formation, and photosynthesis.

• The average integrated power consumption is 21.9 kW with expense of 795.3 Won to maintain the temperature of 14°C.
• 18°C temperature require higher energy and expense.
• Both the power consumption and charges were estimated 64% higher in 18°C over 14°C.
• Every one unit increase in temperature resulted in an increase in power consumption and expense.
• Usually, a farmer in Korea has an average income (spring season) around 4,635,554 Won in 2011.
• These additional costs are estimated to be adequate for Korean farmers budget and also has yield benefit.

• 18°C temperature treatment enhanced good fruit set rate and soluble solid content in the centre part of the fruit.
• Ca²⁺ and Mg²⁺ accumulations were increased in leaves of the fruit set node.
• 18°C temperature treatment had additional/extra costs for power consumption that considered as affordable and in range for Korean farmer budget.
• Modulated temperature treatments could be utilized to enhance the fruit yield and quality in the winter watermelon crops (Citrullus lanatus (Thunb.) Matsum. and Nakai).