Liquid Culture Systems for in vitro Plant Propagation

A new approach for automation 419
population, it is easy to harvest embryo populations of relatively uniform
size: for instance, 95% of the carrot embryos had a size range between 0.4
and 1.6 mm in the population collected when the air flow rate reached the
unit 3 (Figure 1). In the case of coffee, 97% of the embryos measured
between 0.8- 2.2 mm at the airflow rate unit 8 (Figure 2).
As embryo size is an important characteristic for embryo development,
embryos can be roughly sorted according to their developmental stage with
this method. Filtration through nylon meshes of various pore size is a very
simple and useful method for embryo sorting but presents some difficulties
for large volumes of embryo suspensions: the filters should be thoroughly
rinsed and blockage problems are difficult to avoid (Rodriguez et al., 1990;
Ducos et al., 1993a). Sorting dehydrated embryos does not seem to be more
efficient than filtration in liquid medium for size uniformity but it offers the
advantage to be more easily scaled-up. Moreover, other sorting methods
traditionally used for the seeds can be also assessed (e.g. vibrating table,
sifters, alveolus sorter).
3.2 Sowing
Dehydrated embryos did not stick together and bounced in the vibrating
hopper of the seeder like seeds. In the case of carrot, six trays were tested:
72 % of the cells received one embryo and 5 % two embryos (Table 1). In
the case of coffee, the seeder was tested with only one 240-cell tray: as a
preliminary result, the filling rate was 88 % with one embryo and only 1 %
of cells containing two embryos. Coffee embryos could therefore be more
easily sown than carrot embryos probably due to their higher weight. These
filling rates can probably be improved by reducing static electricity inside
the tubes and/or using another type of seeding system in which the seeds are
directly transferred from the nozzles to the trays.
3.3 Germination
To evaluate the embryo capacity to develop into plantlets after automatic
sowing, some carrot embryos were collected on paper at the exit of the tubes
and then sown onto miniplugs. As carrot embryos grow very fast, they
developed into plantlets within 21 days despite contamination (Table 2). The
potential of bare carrot embryos to develop into plantlets was not affected
either by the vibration of the hopper or by the nozzles. Even without
phytoprotection, the conversion rate was not lower than in the control.