Agriculture Reference
In-Depth Information
3.2 Physiological Status of the Donor Plant
The physiological conditions of the donor plant, i.e., the environmental conditions and
age of the donor plant, directly affect both in vitro androgenesis and in vitro gynogen-
esis in almost all plant species. A correlation between plant age and anther response
has also been demonstrated by various scientists. Generally, the first flush of flowers
yields more responsive anthers than those that are born later. Similar is the case with
ovary culture. The frequency of androgenesis is usually higher in anthers harvested at
the beginning of the flowering period and showed a gradual decline in relation to plant
age (Bhojwani and Razdan
1996
). However, it has been reported in
Brassica napus
and
B. rapa
that pollen from older, sickly looking plants yielded a greater number of
embryos than those from young and healthy plants. Varying temperature and light
conditions during the growth of donor plants also affect anther response. In anther cul-
ture of grape, the induction frequency of embyoids, derived from spring flowers, was
higher than that derived from summer flowers (Zou and Li
1981
). The microscopical
observations showed that some varieties of rubber trees often have a lot of degener-
ated and sterile microspores in their anthers, in early spring or hot summer, due to the
influence of unfavourable climatic conditions. As a result, no pollen embryoids were
obtained from such anthers, but only somatic calli were obtained (Chen et al.
1982
).
3.3 Stage of Explants Material at the Time of Inoculation
3.3.1 Stage of Microspores
The stage of microspores at the time of inoculation is one of the most critical factors
for induction of androgenesis. Detailed cytological studies conducted on poplar,
rubber (Chen
1986
) and apple (Zhang et al.
1990
) have shown that androgenic cal-
lus and embryos were mainly induced through a deviation of the first pollen mito-
sis to produce two undifferentiated nuclei. Besides affecting the overall response,
the stage of microspore at culture also has a direct effect on the ploidy of plants
produced in anther culture (Sunderland and Dunwell
1977
). About 80 % of the em-
bryos obtained from binucleate microspores of
Datura innoxia,
a highly androgenic
species, were non haploids (Sunderland et al.
1974
). In a vast majority of species
where success has been achieved, anthers were cultured when microspores were at
the uninucleate stage of microsporogenesis (Chaturvedi et al.
2003
; Pedroso and
Pais
1994
; Sopory and Munshi
1996
).
3.3.2 Stage of the Embryo Sac
It has been reported that the effect of ovule development on gynogenesis is pro-
found as it harbours the embryo sac comprising the egg cell. The stage of embryo
sac is an important determining factor for in vitro gynogenesis in various plant
