Protocols for Micropropagation of Woody Trees and Fruits

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Survival (%) --->
120
100
80
60
40
20
V.M. KULKARNI ET AL.
Shreemanti (b=-0.86)
Basrai (b=-0.79)
Lal Kela (b=-0.76)
N. Rasthali (b=-0.79)
K. Monthan (b=-0.81)
Wild (K) (b=-0.75)
0
0 10 20 30 40 50 60 70 80 100
Dose (Gy) --->
Figure 4. Effect of gamma irradiation on survival (%) of in vitro individual shoots of banana.
In order to dissociate the chimeras, the irradiated shoot-tip multiples are subcultured
for at least 4–8 cycles (M1V0 – M1V4 – 8) on the same proliferation medium. As a trend,
the shoot multiplication ratio during subcultures decreases with increasing dose of
irradiation. However, owing to several growth controlling factors, smooth curves are
difficult to be obtained.
Upon adequate subculturing the individual shoots are separated and transferred for
the induction of rooting (M1V5 – 9). The rooted plantlets are weaned in the greenhouse
and subsequently field planted for evaluation.
An important constraint in evaluating the mutant populations in the case of a
vegetatively propagated crop like banana is to correctly judge at which stage
complete chimera separation could be achieved. Unless this is known, there is
always a risk that the selected mutant may be chimeric and thus will not produce
true-to-type progeny. On the other hand, excessive multiplication in vitro (with a
fear of improper chimera separation) may result in the generation of a large plant
population, unmanageable for field evaluation. Several factors such as the basic
proliferation rates of the non-irradiated cultures and the decreasing proliferation rates
due to irradiation can affect chimera dissociation. It becomes difficult to decide the
“number of subcultures” for dissociating the chimeras subsequent to irradiation of the
shoot-tip multiples.