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Liquid Culture Systems for in vitro Plant Propagation

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190 M. Berthouly & H. Etienne<br />

immersion can be acclimatized directly after root<strong>in</strong>g <strong>in</strong>duction <strong>in</strong> the same<br />

bioreactor (Berthouly et al., 1995). After plant<strong>in</strong>g, the shoots and flowers of<br />

aster plants obta<strong>in</strong>ed from shoot tips grown <strong>in</strong> a temporary immersion<br />

system were larger than those from an agar medium (Tisserat and<br />

Vandercook, 1985). Shoots of radiata p<strong>in</strong>e harvested from a nutrient<br />

replenishment system were very effectively rooted and no decl<strong>in</strong>e <strong>in</strong> root<strong>in</strong>g<br />

ability was found dur<strong>in</strong>g successive harvests <strong>for</strong> 18 months (Aitken-Christie<br />

and Jones, 1987). Given the larger proportion of waxy shoots compared to<br />

wet shoots, which root poorly and have low survival rates (Aitken-Christie et<br />

al., 1985), when compared to a conventional system on agar, us<strong>in</strong>g a<br />

temporary immersion system provided an unexpected bonus dur<strong>in</strong>g the<br />

acclimatization stage. Shoots of grape and Amelanchier alnifolia produced <strong>in</strong><br />

a liquid medium on tilt<strong>in</strong>g mach<strong>in</strong>es also rooted better and more quickly than<br />

those produced on agar media (Harris and Mason, 1983).<br />

Potato tubers propagated <strong>in</strong> a tw<strong>in</strong> flask system could be stored under<br />

room conditions and directly transplanted to soil without any acclimatization<br />

(Akita and Takayama, 1994). Lastly, <strong>in</strong> Coffea arabica, temporary<br />

immersion has enabled mass production of germ<strong>in</strong>ated somatic embryos<br />

capable of successfully regenerat<strong>in</strong>g <strong>in</strong>to plants (70-80% embryo-to-plant<br />

conversion) after direct sow<strong>in</strong>g on horticultural substrate (Etienne-Barry et<br />

al., 1999).<br />

6. Impact of temporary immersion culture on production<br />

costs<br />

The few <strong>in</strong>vestigations carried out so far confirm the spectacular <strong>in</strong>crease<br />

<strong>in</strong> efficiency that could be expected from us<strong>in</strong>g a liquid medium culture<br />

procedure <strong>for</strong> micropropagation. For the proliferation of sugarcane shoots,<br />

Lorenzo et al. (1998) calculated that us<strong>in</strong>g temporary immersion reduced<br />

costs by 46% compared with the standard procedure on an agar medium.<br />

The cost of a shoot produced by temporary immersion was only 0.00104<br />

USD as opposed to 0.00191 USD <strong>for</strong> a shoot produced on agar medium.<br />

This ga<strong>in</strong> primarily resulted from a drastic reduction <strong>in</strong> direct work (from<br />

0.00032 to 0.00004 USD per shoot produced) and <strong>in</strong> the space required <strong>in</strong><br />

culture chambers (from 0.00017 to 0.00009 USD per shoot produced).<br />

Us<strong>in</strong>g temporary immersion to propagate p<strong>in</strong>eapple shoots resulted <strong>in</strong> a<br />

100-fold <strong>in</strong>crease <strong>in</strong> the number of shoots dur<strong>in</strong>g the four-month period<br />

follow<strong>in</strong>g <strong>in</strong>ital culture of the crown buds (Escalona et al., 1999). This<br />

protocol reduced production costs per p<strong>in</strong>eapple plant by 20% when<br />

compared to the conventional method <strong>in</strong> liquid medium. Accord<strong>in</strong>g to the<br />

authors, the key parameters <strong>for</strong> this success were: a reduction <strong>in</strong> the number

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