Plant Gene and Trait 2025, Vol.16, No.5, 234-241 http://genbreedpublisher.com/index.php/pgt 235 2 Principles of High-Density Planting and Drip Irrigation in Bitter Gourd 2.1 Agronomic rationale and yield potential of high-density cultivation High-density planting is achieved by growing more plants in the same area to increase yield. This can enhance the photosynthetic efficiency of the group and also make better use of the land. An appropriate density not only increases the number of fruits and the yield per unit area, but also improves ventilation and light transmission by adjusting the distribution of branches and leaves, thereby reducing diseases. For instance, the optimal density for grafting bitter gourd in a greenhouse is 70 to 100 plants per 667m². By pruning weak and low-lying branches in combination, the yield and fruit quality can be further enhanced. However, high density should also take into account the variety and growth environment. If the density is too high, it may cause the plants to compete for water and nutrients, resulting in smaller individual fruits. 2.2 Role of drip irrigation in optimizing water and nutrient delivery Drip irrigation is a method that can precisely deliver water and fertilizer to the roots. It can enhance water use efficiency (WUE) and fertilizer utilization rate. Studies have shown that bitter gourd with drip irrigation combined with appropriate fertilization (such as NPK 150:120:120 kg/ha) can significantly increase yield and fruit weight, and the water productivity under drip irrigation is much higher than that under traditional irrigation (Turkar and Deshmukh, 2018; Bahadur et al., 2021). Drip irrigation can also reduce water evaporation and nutrient loss, lower the risk of soil salt accumulation, and improve the stress resistance and quality of crops (Singh et al., 2020; Soomro et al., 2021). If drip irrigation is combined with plastic film mulching, it can better retain moisture, suppress weeds, and promote early maturity and high yield (Kayande et al., 2016; Abraham et al., 2018). 2.3 Integration of planting density and irrigation scheduling for growth optimization Combining high-density planting with drip irrigation is an important method for achieving high yields and efficiency of bitter gourds. Density, irrigation and fertilization should be properly coordinated to ensure that each plant receives sufficient water and nutrients and avoid excessive competition for resources. Studies have found that under drip irrigation conditions, irrigating at 100% crop evapotranspiration (ET) per day, combined with high-density planting, can significantly increase yield and water use efficiency (Singh et al., 2020; Bahadur et al., 2021). In addition, staged and batched water and fertilizer supply (such as NPK drip irrigation once every 7 days) can better meet the needs of different growth stages, enabling continuous growth and high yield of bitter gourd (Turkar and Deshmukh, 2018). In the specific implementation, it is also necessary to adjust the density and irrigation plan according to the variety, climate and soil conditions, so as to maximize the utilization of resources and achieve high yield (Xu et al., 2023). 3 Morphological Traits Related to High Yield 3.1 Vine length, branching patterns, and canopy architecture The length of the vine and the number of branches are important foundations for high yield of bitter gourd. Plants with longer vine lengths and more branches usually have a larger photosynthetic area, stronger growth vigor, are more likely to bear more fruits, and increase the yield per plant (Gupta et al., 2016; Lavale et al., 2022). Under high-density planting and drip irrigation conditions, a reasonable canopy structure can make the light distribution more uniform, reduce leaf overlap, improve photosynthetic efficiency, thereby promoting fruit development and increasing yield (Selvam et al., 2020; Bahadur et al., 2021). Different branching types and canopy structures also provide abundant genetic materials for breeding high-yield varieties (Alhariri et al., 2021; Mallikarjuna et al., 2024). 3.2 Leaf morphology, chlorophyll content, and photosynthetic efficiency Leaf morphology (such as leaf area, leaf shape, and leaf thickness) directly affects photosynthesis. High-yield groups usually have large leaf area and high chlorophyll content, which can increase the photosynthetic rate per unit area (Mehta et al., 2024). Drip irrigation can maintain the water content and chlorophyll content of leaves, further improving photosynthetic efficiency and dry matter accumulation (Bahadur et al., 2021). The research also found that the heritability of leaf traits is relatively high and the selection potential is large, which is an important direction for high-yield breeding (Panigrahi et al., 2024).
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