Caulerpa racemosa is a green seaweed or well-known sea grape that is an economically important macroalgae species of the genus Caulerpa (Caulerpaceae, Chlorophyta) utilized for local consumption and international trade in Southeast Asian countries (Kandhasamy and Arunachalam 2008; Pereira 2016; Dumilag 2019). Sea grapes contain nutrients such as nitrogen, magnesium, and iron. Seagrapes contain high mineral content, nitrogen, magnesium, iron, protein, polyunsaturated fatty acids (PUFAs), and vitamins (Gabrielsen 1996; Saito et al. 2010; Peña-Rodriguez et al. 2011; Nagappan and Vairappan 2014). Based on nutrient analyses, C. racemosa thalli contain 3.60% total nitrogen, 0.938% potassium, 0.614% phosphorous, 16.79% calcium, 0.75% magnesium, 0.018% sulphur, 1.05 ppm iron, 14.95 ppm copper, and 36.13 ppm zinc (Chapman and Chapman 1980).
In Indonesia, locally known as “Latoh”, it is used as “pecel” or salads. C. racemosa cultivation has been carried out in Indonesia, including in Sulawesi, Nusa Tenggara and Jepara, Central Java. According to DJPB data (2017), the demand for Caulerpa increases yearly, both nationally and internationally. National seaweed data for five years (2011–2015) shows a positive upward trend, with an average increase of 22.25%. Increased demand must be accompanied by increased production as well. The problem that arises is that C. racemosa has not been maximized. Improving the quality of seeds to boost growth is one strategy to solve this challenge. Seaweed grows due to the processes of respiration and photosynthesis that it performs.
Synthetic plant growth regulators alter the plant's quality and potentially harm human consumption. Plant growth regulators (PGRs) can improve physiological efficiency, including photosynthetic ability, thereby helping in effective flower formation, seed, and fruit development and ultimately enhancing the productivity of the crops (Solaimalai et al. 2001). However, the excessive use of PGRs and their degradation products have side effects on human health, animals, and plants. The residues of PGRs in agricultural products are seriously detrimental to human health because they have been found with hepatotoxicity, neurotoxicity, carcinogenicity, and other side effects. Furthermore, PGRs are suspected of disrupting human and animal reproductive systems (Xu 2018; Chen et al. 2022).
Currently, efforts are being made to boost growth by making plant growth regulators from natural materials. The role of growth regulators has been documented in hundreds of herbaceous crops (Kavina et al. 2011). Some marine natural materials have been used as PGRs, such as Ulva, Padina, and Sargassum (Garcia et al. 2020). In addition to using marine natural materials, natural PGRs from land plants are widely used. Coconut water has auxins, gibberellins, and cytokinins (Mamaril 1988; Mintah et al. 2018; Aisa et al. 2020; Estevez 2021); Moringa leaves containing zeatin (Culver et al. 2012; Maishanu et al. 2017); mung bean sprouts containing abscisic acid (ABA), gibberellin (GA), jasmonic acid (JA), and indole-3-acetic acid (IAA) (Holdsworth et al. 2008; Linkies and Leubner 2012; Miransari and Smith 2014); maize containing cytokinin (Schmülling et al. 2003; Heyl et al. 2012; Murai et al. 2014); shallots containing auxin (Yunindanova 2018), and Eucheuma cottonii containing auxin, gibberellin, and cytokinin (Sedayu et al. 2013;). These natural materials, such as PGRs, are mainly used on higher plants, but it has rarely been investigated on low-level plants such as seaweed. Hence, this study aimed to determine the effectiveness of aqueous extract from various plants as exogenous plant growth regulators (PGRs) in the morphology, growth, and nutrition of C. racemosa.