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... INTRODUCTION
Orchidoid mycorrhizae (OM), as the name suggests, are characteristics of roughly the 20,000 species in the orchid family, and are not known in any other group. ... Like other mycoparsitic plants, they have a number of structural specializations to this way of life, including their own distinctive form of mycorrhiza.
Orchid Seeds
Orchid seeds are dust-like, consisting of a tiny spherical embryo with no endosperm and a thin seed coat (Arditti & Ghani, 2000). ... Once fungal contact has been made, the orchid seedling grows unto a callus-like lump of tissue termed a protocorm (which corresponds to the hypocotyls and radicle of other plants). ...
The fungi
All orchid mycorrhizal fungi are able to obtain carbohydrate from outside the orchid although there is some diversity of source (Smith and Read, 1997). ... Orchid fungi have unspecialised requirements for nutrients other than carbon sources. ...
Nevertheless, orchid mycorrhiza has an impact on plant fitness from germination through seedling stage and in many cases throughout life. But perhaps one of the most interesting areas of OM studies lies in the initial infection and subsequent germination of orchid seeds in nature by orchid mycorrhiza. As such, this paper aims to give an overview of the latest findings regarding OM as a factor that affects the recruitment (and subsequent infection) of orchid seeds as well as their ecological and/or substrate distributions. ... OM AS A FACTOR IN THE RECRUITMENT AND DISTRIBUTION OF ORCHID SEEDS
The great seed production in orchids suggests that the mortality of seeds and seedlings is exceedingly large. Unsuitable substrate and adverse physical conditions are challenges to any viable seed, but orchid seeds have the additional problem of locating a compatible mycobiont (Rasmussan, 2002). ... , 2002), the recruitment of orchid seeds as well as an indication of the natural situation for germination, is to be obtained. ... These findings strongly suggest that OM exudates are essential in ensuring the inhibition or localization (and subsequent germination) of some species of orchid seeds. ... , 1996) have opened new possibilities for analysing germination behaviour, fungal availability and natural substrates as they affect orchid seed recruitment. ... pubescens was able to germinate freely in the ground without mycorrhiza infection. However, the seedlings are not always successful in establishing mycorrhiza and high seedling mortality follows (Fig. ... Size represented as maximal width of the turnip shape seedlings with established visible mycorrhiza. ... 2: Symbiotic germination is necessary in Liparis lilifolia with a range of orchid endophytes (labelled M-). ...
One other important substrate factor that was found to determine the recruitment and germination of orchid seeds is water availability. ... (2000) demonstrated that mycorrhizal fungi were able to significantly facilitate the germination of orchid seed hosts. ... The interaction between embryo and fungus can have three basic outcomes: (a) a mycorrhizal interaction, with the formation of pelotons which are later lysed; (b) a parasitice interaction, in which the orchid cells are invaded by relatively disorganized hyphal growth and death of the protocorm results.
Approximate Word count = 2240
Approximate Pages = 9
(250 words per page double spaced)
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