EARLY SHOOT AND DIAMETER GROWTH IN FOUR <em>PINUS</em> <em>MERKUSII</em> POPULATIONS FROM THAILAND

Abstract

Early shoot and diameter growth in four Pinus merkusii populations from Thailand was monitored between the ages of 8 and 47 weeks under controlled environment. Based on earlier studies concerning shoot development of the grass stage P. merkusii seedlings, it was hypothesised that the northern high-altitude populations have slower shoot growth and faster diameter growth than the northeastern low-altitude populations. Variation in timing of shoot and diameter growth among the populations was also investigated. Statistically significant variation in hypocotyl length and total shoot and diameter growth during the experiment was found among the populations. The timing of shoot and diameter growth was similar in all populations. A short hypocotyl length seems to indicate slow shoot growth during the early grass stage. This suggests that hypocotyl length can provide indicative information concerning the duration of the grass stage. The results also confirmed the earlier findings that there is genotypic variation in the rate of progress through the grass stage among the mainland Southeast Asian populations. However, the results did not verify the assumption that the high-altitude populations have slower shoot growth and faster diameter growth than the low-altitude populations. Only one of the two high-altitude populations exhibited rather slow shoot growth during the experiment, whereas the other exhibited significantly faster shoot growth which was similar to the low-altitude populations. Furthermore, only one of the low-altitude populations differed significantly from the high-altitude populations with the slowest total shoot growth. Slow shoot elongation seems be related with intensive diameter growth and vice versa during the early grass stage. Genotypic variation in total diameter growth suggests that there is also variation among the populations in their ability to withstand fire.