School of Agriculture, Food and Ecosystem Sciences - Theses

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    The effect of desiccation on the germination of some tropical tree seeds
    Syamsuwida, Dida ( 1991)
    The aim of this study was to investigate the influence of desiccation on the germination behaviour of some tropical tree seeds when tested under controlled conditions following exposure to different moisture regimes. The results were used to classify the seed of the observed species into the physiological categories of recalcitrant or non-recalcitrant and to provide practical recommendations for effective storage. Six species of tropical tree seeds, Cryptocarya triplinervis, Neolitsea caalbata, Acmena hemilampra, Podocarpus elatus, Azaarachta indica and Pittosporum rubiginosum were either forced dried at 300 C (22-28% RH), or dried slowly at 200 C (52-64% RH). The water content of the seeds was measured during drying and the percentage loss in water content and the rates of drying varied for different species. All seeds, except for A. indica were stored for two months at room temperature (230 q and at 40 C. A. indica seeds were stored in either (i) a desiccator with silica gel as a desiccant, (ii) a jar where the seeds were sterilized on the surface or (iii) laminated - polyethylene bags placed in a freezer. The period of storage was 6 weeks and the seeds were removed periodically to assess the viability. The embryo and the female gametophyte of P. elatus seeds were measured after 7 and 14 days of incubation to determine structural changes in the seeds due to the effect of desiccation. An investigation of the effect of the pattern of drying on subsequent seed quality of some of the species (C. triplinervis , A. indica and P. rubiginosum ) showed that the rapid drying gave better viability. On the other hand, the rapid drying method resulted in a gradual loss of viability of N. dealbata and P. elatus seeds. However, both of drying patterns did not so damage A. hemilampra seeds. The critical seed moisture content below which seeds could not recover from desiccation were 30% for C. triplinervis, 7% for N. dealbata, 35%- 37% for P. elatus and 13 5%f or P. rubiginosum. A. hemilampra seeds remained viable at a moisture content of 29% The lowest moisture content for A. indica was not determined because the viability of seeds was reduced during the experiment. The viability of seeds of C. triplinervis, A. hemilampra and P. elatus can be maintained after 10 weeks storage at 40 C given the maintenance of high moisture content. However, N. dealbata and P. rubiginosum seeds should be kept at 40 C because of the relatively low moisture content. Placing the seed in a desiccator gave the best result for A. indica. C. triplinervis, P. elatus and A. indica seeds may be categorized as recalcitrant. N. dealbata and P. rubiginosum seeds should be classified as non-recalcitrant species. A. hemilampra seed cannot yet be classified because the critical moisture content is not yet known. There were structural differences in the seed components of P. elatus during the course of germination due to desiccated either by rapid or slow drying.