Factors controlling teak (Tectona grandis Linn. f.) seed germination and their importance to Thailand

Abstract

The economic importance of teak with its high value and high quality wood has long been recognized. Consequently the species is now widely planted and the rate of plantation establishment is increasing every year. Currently in Thailand the annual teak planting programme is about 10,000 ha. There are however difficulties in establishing large scale plantatations of teak because of poor and erratic germination. A review of current germination procedures indicated that none of the methods used were reliable and there existed no definite procedures which consistently yielded improved germination. A series of preliminary studies were set up to investigate conditions and procedures which might affect teak germination. These indicated heat treatment under dry conditions was effective. The moisture regime in the soil in which the germinating seed was placed was also an important factor controlling germination. High temperature regimes of the order of 30°C or more also appeared to favour teak seed germination. The following pre-sowing treatments were not effective and could be deleterious: (a) using fuily extracted seeds for sowing, (b) the procedures of soaking and drying, (c) wet pre-treatments, (d) cold pre-treatments. These initial studies also examined the relationship between germination and the subsequent growth of the seedlings. Grading of teak drupes in each seed batch before sowing and also ensuring each seed batch was sown separately would reduce inter-plant competition in the seedbed and should increase the number of usable seedlings produced. Following the preliminary studies further investigations were carried out and to define: (i) the optimum procedures for heat treatment; (ii) the moisture regimes and moisture content of the soil medium favourable for teak germination under laboratory conditions. The recommended procedures were: (i) dry heat treatment at 80°C for 48 hours before sowing; (ii) the most favourable moisture content for teak germination varied with soil type and characteristics. In the perlite and vermiculite the optimum soil moisture content was around 200% and in the sand about 11% or lower. For a mixture of perlite and vermiculite a twice-daily watering was the best. The studies also confirmed previous reports that seed germination improved with seed age. The heat pre-treatment procedure was less effective in old seed and this suggested that there may be some similarity between heating and the after-ripening process. There is, however, a need for further and detailed study of this.