Effects of the plant growth regulator NAA on young fruit drop prevention and seed quality of Ngoc Linh ginseng (Panax vietnamensis Ha et Grushv.)

Ngoc Linh ginseng (Panax vietnamensis Ha et Grushv.) is a rare and highly valuable medicinal plant endemic to Vietnam, whose large-scale cultivation is constrained by low fruit set, early fruit drop and limited seedling quality. This study evaluated the effects of different concentrations of the plant growth regulator Naphthalene Acetic Acid (NAA) on flower and fruit development, seed quality, seed germination and seedling growth of Ngoc Linh ginseng under nursery conditions. The experiment was conducted from March 2022 to March 2024 at Ngoc Linh Mountain, Quang Nam Province, using four treatments: water spray (control) and foliar application of NAA at 20, 30 and 40 ppm, arranged in a randomized complete block design. The results showed that NAA application significantly influenced reproductive and seedling-related parameters compared with the untreated control. NAA at 30 ppm produced the most favorable outcomes, increasing the number of flowers per inflorescence (61.63 flowers), flower stalk length (1.43 cm), flower diameter (3.59 mm), and the number of fruits per cluster (44.08 fruits). Fruit quality was also improved, with the highest proportion of red fruits (>46%) and the lowest proportion of green fruits. In addition, seed treatment with NAA at 30 ppm resulted in the highest germination rate (78.89%), seedling formation rate (75.56%) and proportion of marketable seedlings (74.11%). Seedlings from this treatment exhibited superior growth performance, including greater plant height, canopy diameter, and the highest weight of 100 tubers (132.65 g). Overall, foliar application of NAA at a concentration of 30 ppm is recommended to enhance flower and fruit set, improve seed quality and promote seedling growth of Ngoc Linh ginseng, thereby contributing to the development of a standardized and sustainable seedling production system.