Improvement of seedling quality of red jabon (Neolamarckia macrophylla (Roxb.) Bosser) through seed sowing techniques and seed invigoration

Abstract Red jabon (Neolamarckia macrophylla) is one of potential tree species, but there are some problems in its cultivation. Intermediate seed character and very small seed sizes with little food reserves often cause the low germination, low growth of the seedlings, and the sowing of the seeds to be too dense, resulting in an abnormal number of seedlings. The purpose of the research was to improve the seed germination and seedling quality of red jabon by adjusting the sowing density and seed invigoration treatment using hormonal and biopriming. Two experiments were conducted, that is, (1) identification of optimal seed density on the several combinations of sowing media (top soil, rice husk and compost) and (2) evaluation of the most suitable hormonal priming (GA3) and biopriming (liquid organic fertilizer, LOF) applications. The use of top soil media with a seed density of 0.5 g/400 cm2 can produce the highest pure live seed (PLS), that is, 721.67 seedlings/0.5 g. The seed treated by hormonal and bio-priming significantly affected the seed germination and seedling growth. Soaking seed in GA3 100 ppm for 4 days produced the highest of the PLS (764 seedlings/0.5 g), followed by soaking in LOF for 3 days and GA3 50 ppm for 4 days. The highest seedling height was generated from soaking the seeds using LOF for 3 days. The highest root collar diameter and biomass of red jabon seedlings were obtained from the treatment of seeds immersed in the GA3 50 ppm for 3 days. The best quality index value of red jabon seedlings was produced from the treatment of seeds immersed in the hormone GA3 50 ppm for 3 days. In general, a sowing density of 0.5 g/400 cm2 in top soil media and seed soaking treatment in GA3 50 ppm or LOF for 3 days can improve germination and growth of red jabon seedlings.