Agriculture Reference
In-Depth Information
metal treatments are particularly popular approaches in anther and microspore cul-
tures (Shariatpanahi et al.
2006
).
Temperature treatment is considered to be the most effective treatment to induce
pollen embryogenesis and it may be applied to excised flower buds or whole inflo-
rescences before culture or cultured anthers or pollen grain, prior to their transfer
to standard culture room conditions, in order to divert the gametophytic pathway to
sporophytic mode of development. The optimum temperature and duration of pre-
treatments vary with the genotype. Cold pre-treatment (4 °C for 2-3 days) is em-
ployed routinely in the anther culture of many crops and its effect is also genotype-
dependant (Osolnik et al.
1993
; Powell
1988
). In
Brassica
species, a short-duration
high temperature pre-treatment at 30-35 °C to cultured anthers before shifting them
to 25 °C is required to efficiently switch the developmental pathway.
Light does not seem to be necessary for the induction of androgenesis. For pollen
culture of
Datura innoxia
(Sangwan-Norreel
1977
),
Nicotiana tabacum
(Sunderland
and Roberts
1977
) and
Annona squamosa
(Nair et al.
1983
), an initial incubation of
cultures in dark, followed by diffuse light was found to be suitable. Isolated pollen
cultures are more sensitive to light than anther cultures (Nitsch
1977
). In
Brassica
juncea
(Sharma and Bhojwani
1989
) and
Hordeum vulgare (
Xu
1990
) species, light
is detrimental even for anther cultures. Likewise, neem callusing from microspores
requires continuous dark incubation of anthers (Chaturvedi et al.
2003
).
A beneficial role of cold treatment on gynogenesis has been reported in some
species whilst in others, no significant effects on gynogenesis were observed. Pre-
treating the capitula of sunflower at 4 °C for 24-48 h before culture, significantly
increases the induction frequency (Yan et al.
1987
). Cai et al. (
1988
) observed a
promotory effect of cold treatment to young panicles of rice at 7 °C for one day
prior to ovary culture in gynogenesis. In
Cucumis melo,
pollination of pistils with ir-
radiated pollen is essential to obtain ovules capable of forming gynogenic haploids
(Katoh et al.
1993
).
3.6 Other Miscellaneous Factors
3.6.1 Anther Wall Factor
One of the important research subject in anther culture for woody plants is to avoid
the over-proliferation of callus from anther wall tissues and to achieve a high yield
of pollen embyoids and pollen calli. In anther culture of most woody plants, both
pollen calli or embryoids and somatic calli from anther wall tissues grow simulta-
neously. The development of callus from somatic tissues of anther can be avoided
by culture of isolated microspores. However, there are not many successful reports
on microspore culture in woody plants (Chaturvedi et al.
2003
). Pelletier and Ilami
(
1972
) had introduced the concept of “wall factor”, according to which the somatic
tissues of anther play an important role in the induction of sporophytic divisions in
pollen. In anther culture of rubber, 47 % of the microspores in close contact with
