Agriculture Reference
In-Depth Information
aration of pollen at the developmental stage, most suitable for androgenesis, can be
obtained by gradient centrifugation. Isolated pollen can be modified genetically by
mutagenesis or genetic engineering before the culture and a new genotype can be
selected at an early stage of development. Some of the important factors that affect
induction of androgenesis in cultured pollen are the composition of the culture medi-
um, pre-treatment and plating density. In most of the cereals, pollen culture involves
pre-culture of the anthers for a few days or co-culture of pollen with a nurse tissue.
Treatment of pollen-derived embryos and pollen derived callus to recover complete
plantlets is similar to that of anther culture. However, the nutritional requirements of
isolated pollen in culture are more complex than those of cultured anthers.
2.2 Gynogenesis
As mentioned earlier, in vitro gynogenesis is used as a complementary technique in
species where anther/pollen culture is inaccessible or unsuccessful. Young flowers,
ovaries or ovules have been used as explants to produce gynogenic haploids where
the plants develop from unfertilized cells of female gametophyte (embryo sac) ei-
ther through direct embryogenesis or via callusing. The following techniques are
generally used for production of haploids via in vitro gynogenesis.
2.2.1 In situ Parthenogenesis Induced by Irradiated Pollen
Followed by In Vitro Embryo Culture
Parthenogenesis induced in vivo by irradiated pollen followed by in vitro culture
of embryos can be an alternative method of obtaining haploids in fruit crops. Gy-
nogenesis by
in situ
pollination with irradiated pollen has been successfully used
for
Malus domestica
(L.) Borkh (Zhang and Lespinasse
1991
),
Pyrus communis
L.
(Bouvier et al.
1993
),
Actinidia deliciosa
(A. Chev) (Pandey et al.
1990
; Chalak
and Legave
1997
). This method is based on in vitro culture of immature seeds or
embryos, obtained as a result of pollination by irradiated pollen with gamma rays
from cobalt 60. The method is useful in those species in which in vitro anther cul-
ture has not been successful. Irradiation does not hinder pollen germination but
prevents pollen fertilization, thus stimulating the development of haploid embryos
from ovules. The success of this technique is dependent on the choice of radiation
dose, the developmental stage of the embryos at the time of culture, culture condi-
tions and media requirements.
2.2.2 Ovary Slice Culture
Ovary slice culture technique involves culture of transverse sections of unpollinated
ovaries on culture media. The various steps of ovary slice culture of tea are sum-
