Plant Gene and Trait 2025, Vol.16, No.5, 234-241 http://genbreedpublisher.com/index.php/pgt 237 5.3 Interaction with nutrient uptake and morphological expression Drip irrigation fertilization (integrated water and fertilizer) can greatly improve the efficiency of bitter gourd in absorbing nutrients such as nitrogen, phosphorus and potassium (Mali et al., 2017). This not only makes the root system absorb nutrients more efficiently, but also directly reflects in the plant morphology, such as thicker vines, thicker leaves, and better fruit development. Drip irrigation fertilization can also increase the dry matter and nutrient content of fruits. However, when the water and fertilizer levels are too high, it may reduce the content of some antioxidant substances (such as vitamin C) (Abraham et al., 2018). In addition, drip irrigation can also regulate the rhidal environment, promote the activities of beneficial microorganisms, and indirectly optimize the morphological performance of plants (Figure 1) (Wang et al., 2024). Figure 1 (a) Soil microstructure under different treatments and (b) distribution of soil pores under different treatments: white areas represent pores and black areas represent soil particles (Adopted from Wang et al., 2024) 6 Morphological Indicators of High-Yield Bitter Gourd Populations 6.1 Key morphological traits linked to yield performance The yield performance of high-yielding bitter gourd is closely related to many morphological traits. It is generally believed that traits such as fruit weight, fruit length, fruit diameter, fruit quantity, flesh thickness and vine length are significantly positively correlated with the yield per plant and are important references for judging high yield (Iqbal et al., 2016; Yadagiri, 2017; Liu, 2024). Among them, fruit weight (r=0.81), fruit length (r=0.73), flesh thickness (r=0.65), and fruit diameter (r=0.63) had the strongest correlations with yield (Wan et al., 2022). In addition, early flowering and a high ratio of male to female flowers will also directly affect the yield (Prasanth et al., 2020). 6.2 Trait stability and variability under combined treatments Under conditions of high-density planting and drip irrigation, these yield traits usually have high heritability and significant genetic progression, indicating that they are mainly controlled by genes and have less environmental influence, making them suitable for improvement through phenotypic selection (Panigrahi et al., 2024). For instance, the heritability of traits such as fruit weight, fruit length, fruit quantity and vine length all exceeds 90%, and they remain stable in different environments, which can be used as important selection indicators for high-yield breeding (Mehta et al., 2021). However, traits such as fruit surface nodules and fruit color are greatly affected by the environment. It is best to combine molecular marker-assisted selection to improve breeding efficiency (Mallikarjuna et al., 2024). 6.3 Potential morphological markers for selection in breeding programs Overall, fruit weight, fruit length, fruit diameter, fruit quantity, flesh thickness and vine length are not only closely related to yield, but also have high heritability and improvement potential, and are ideal reference traits for high-yield breeding (Mehta et al., 2021; Mallikarjuna et al., 2024). In addition, early flowering, the ratio of male to female flowers, fruit nodules and fruit color, etc. can also be used as auxiliary references. Especially in
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