V. P. G. Moura
Published: 1977
Total Pages: 168
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Eucalyptus urophylla S.T. Blake is a tropical species occurring naturally in a group of islands of the Lesser Sunda Archipelago, beteween 6 and 10 latitude Sourth and between 188 and 128 longitude East. E. urophylla grows in a wide range of soils from almost sea level to 2980 meters in altitude. The climate ranges from hot to cool tropical conditions with a pronounced dry seasson of about three months in the winter. A study was made of genetic variation in E. urophylla taken from an altitudional transect mostly in East Timor with the exception of one seed sample which came from 600m altitude in the nearby island of pantar. The physiological basis of the genetic variation with altitude was examined by growing seedlings fram six altitudes, 600, 1200, 1500, 2100m and 2740m, under controlled conditions. The seeds were found to vary in size with altitude, being larger in the provenances from higher altitudes. Cotyledon size was dependent on seed size and strongly affected the early seedling growth, larger cotyledons resulting in larger seedlings up to four weeks of age. After four weeks the positive relationship of cotyledon size and seedling growth changed, firstly disappearing in the six-week-old seedlings then becaming negative in seedlings at eight weeks of age. The germination of seeds in a range of constant temperature (10 to 40) showed that all provenances germinated equally weel between 20 and 32 C, with an optium around 31C. These was a slightly superior rate of germination of the high altitude provences at the lawest temperature regime. Seedlings grown at four temperatures (12, 20, 25 and 30 C) fram 12 to 22 weeks age showed that all provenances grew best at the two highest temperatures. Howeres, differences were found between provenances with a trend to decreased height and dry weight with increasing altitude. This trend was associated with changes in certain characters. Leaf size and internode length decreased with rise in altitude of seed provenance while leaf thickness increased with altitude. Two conclusions are drawn with regard to field plantations o f E. urophylla in the tropics. The firsts is that seedling selection shoud be delayed until the age at least eight weeks in order to avoid the overriding influence of seed and cotyledon size the early growth of seedlings. The second is that low altitude populations are better adapted to grow in high temperature conditions, but high altitude populations are likely to be more successful in the cool conditions found at high altitudes.
