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Liquid Culture Systems for in vitro Plant Propagation

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

3.1 Shoot proliferation and microcutt<strong>in</strong>gs<br />

A great deal of work has proved that temporary immersion stimulates<br />

shoot proliferation. In 1987, Aitken-Christie and Jones showed better shoot<br />

growth could be obta<strong>in</strong>ed <strong>for</strong> radiata p<strong>in</strong>e with a method <strong>in</strong>volv<strong>in</strong>g<br />

replenishment of a liquid nutrient medium than with monthly transfers on an<br />

agar medium. This system enabled cont<strong>in</strong>uous shoot growth and monthly<br />

harvests <strong>for</strong> 18 months, without transferr<strong>in</strong>g the plant material. Shoots<br />

obta<strong>in</strong>ed with partial and temporary immersion <strong>in</strong> the nutrient medium were<br />

longer and of better quality than those obta<strong>in</strong>ed on agar media. A complete<br />

and conv<strong>in</strong>c<strong>in</strong>g demonstration of the efficacy of temporary immersion was<br />

carried out <strong>for</strong> the proliferation of banana meristems. Alvard et al. (1993)<br />

showed that apply<strong>in</strong>g liquid medium strongly <strong>in</strong>fluenced the development<br />

and proliferation rate <strong>for</strong> micropropagated banana explants. When four<br />

liquid medium culture methods were compared to the conventional method<br />

on agar medium, they obta<strong>in</strong>ed the follow<strong>in</strong>g results after cultur<strong>in</strong>g <strong>for</strong> 20<br />

days: i) shoots placed <strong>in</strong> a simple liquid medium or on a cellulose support<br />

barely proliferated or not at all; ii) shoots on an agar medium, those<br />

subjected to partial immersion and those <strong>in</strong> a bubble-aerated medium had<br />

multiplication rates of 2.2 to 3.1 and, iii) the highest proliferation rate (>5)<br />

was found <strong>for</strong> explants subjected to temporary immersion <strong>in</strong> the medium.<br />

These authors obta<strong>in</strong>ed their results us<strong>in</strong>g a RITA � bioreactor, with 20 m<strong>in</strong><br />

immersions every 2 h. A Cuban team obta<strong>in</strong>ed similar results with banana,<br />

us<strong>in</strong>g the tw<strong>in</strong> flasks system (Teisson et al., 1999).<br />

Serviceberry shoots (Amelanchier x grandiflora Rehd. ‘Pr<strong>in</strong>cess Diana’)<br />

were cultured <strong>in</strong> the temporary immersion system described by Simonton et<br />

al. (1991) and compared to those obta<strong>in</strong>ed either on agar medium or <strong>in</strong> liquid<br />

medium <strong>in</strong> baby food jars, and on agar medium or <strong>in</strong> non-cycl<strong>in</strong>g liquid<br />

medium <strong>in</strong> a 7-litre vessel (Krueger et al., 1991). A comb<strong>in</strong>ation of liquid<br />

medium, a 7-litre recipient vessel and <strong>in</strong>termittent contact with the liquid<br />

medium gave significantly higher proliferation rates than <strong>in</strong> any other<br />

comb<strong>in</strong>ation tested. Compared with conventional treatment (agar medium <strong>in</strong><br />

baby food jars), cultures that grew <strong>in</strong> <strong>in</strong>termittent contact with the culture<br />

medium gave higher values <strong>for</strong> the number of shoots (x 2.6), shoot weight (x<br />

2.1), shoot length (x 1.2) and culture weight (x 2.2).<br />

With sugarcane, Lorenzo et al. (1998) also showed with the Tw<strong>in</strong> Flasks<br />

system that temporary immersion clearly stimulated shoot <strong>for</strong>mation and<br />

length. The multiplication rate (23.9 shoots per 30 days) <strong>in</strong>creased by 6<br />

compared with the standard protocol (3.96 shoots per 30 days; Jiménez et<br />

al., 1995). Similar results were obta<strong>in</strong>ed with another 3 genotypes. Likewise,<br />

Escalona et al. (1999) used the same bioreactor <strong>for</strong> p<strong>in</strong>eapple meristem<br />

propagation to show that temporary immersion stimulated the multiplication

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