<![CDATA[Siam orange (Citrus nobilis L.) is widely propagated by grafting because it produces seedlings identical to the parent plant and shortens the vegetative phase. The success and vigor of grafted seedlings can be improved by applying plant growth regulators (PGRs) of natural or synthetic origin, yet different PGR types may produce different responses. This study aimed to determine the effect of different PGR types on the growth and graft union of grafted Siam orange seedlings and to identify the most effective type. The research was conducted at CV. Diplomat Kantor Barat, Batu City, Indonesia, from March to July 2024, using a non-factorial Randomized Block Design with nine treatments and three replications: Z0 (control), Z1 (young coconut water), Z2 (old coconut water), Z3 (shallot extract), Z4 (mung bean sprout extract), Z5 (NAA), Z6 (BAP), Z7 (IBA), and Z8 (GA₃), each at 200 ppm. The observed variables were survival percentage, shoot height, number of leaves, leaf area, shoot diameter, and graft union. Data were analyzed using ANOVA followed by the Honestly Significant Difference test at 5%. The results showed that GA₃ (Z8) produced the highest shoot height, number of leaves, leaf area, and shoot diameter, owing to its higher gibberellin content. Synthetic PGRs generally outperformed natural PGRs and the control, while NAA (Z5) and IBA (Z7) produced the best graft union, indicated by a minimal gap between scion and rootstock due to their high auxin content.]]>
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