Agriculture Reference
In-Depth Information
species. However, it is difficult to know the stage of embryo sac at the time of in-
oculation. Several authors prefer to describe the inoculation stage according to the
developmental stage of the flower bud or stage of pollen development. However,
this could not be possible in several species, where male and female gametophytes
do not mature simultaneously, a phenomenon known as protandry, the maturation
of anthers before carpels (e.g., onion, leek, sunflower, sugar beet, carrot,) and the
opposite protogyny (e.g., pearl millet). In such cases, the stage of embryo-sac at
culture can be determined by histological preparations of ovary/ovules that are at
identical stage with that of cultured ovary/ovules (Srivastava et al.
2009
).
The unpollinated ovules collected two or three days before anthesis were non
responsive on culture media as has been reported in Niger whereas unpollinated
ovules collected one day before anthesis were most responsive with about 5 to
13.3 % embryogenesis recorded (Bhat and Murthy
2007
). Although a wide range of
embryo sac stages are responsive to gynogenic development, in most cases, nearly
mature embryo-sac stage gave better results. This is quite contrary to anther culture
in which mature pollen is nonresponsive to androgenesis. In barley and rice, unfer-
tilized ovary cultures with late staged mature embryo sacs gave good results (San
Noeum
1976
,
1979
; Wang and Kuang
1981
) while others reported success with
ovary cultures containing uninucleate to mature embryo sacs (Zhou and Yang
1981
;
Yang and Zhou
1982
; Kuo
1982
; Huang et al.
1982
).
3.4 Culture Media
3.4.1 Basic Media
The constituents of the basal medium and combinations of growth regulators serve
as an important factor in eliciting successful androgenesis and gynogenesis. How-
ever, it is difficult to suggest one single culture medium with a particular growth
regulator for all the systems. Regeneration of androgenic and gynogenic plants may
occur directly via embryogenesis or via callus formation from pollen/egg cell, fol-
lowed by organogenesis. In the later stages of plant development, the media constit-
uents may vary according to culture conditions and requirement by the plant itself.
Most species exhibit androgenesis on a complete nutrient medium (mineral salts,
vitamins and sucrose) with or without growth regulators. Most commonly used bas-
al media for anther culture are N
6
(Chu
1978
) medium, MS (Murashige and Skoog
1962
) medium with slight modifications, Nitsch and Nitsch (
1969
) medium, and B5
medium (Gamborg et al.
1968
). Half strength MS medium is suitable for Solana-
ceae and N
6
medium has been used for cereals (Chu
1978
).
Most early work in 1950s used Nitsch medium for unpollinated ovule and ovary
culture; however since the 1970s, Miller (
1963
), MS or N
6
media have been used
in successful experiments. In
Gerbera
, MS seems better than the Knop's and Heller
medium (Cagnet-Sitbon
1980
). An increase in the content of B group vitamins and
glycine in H medium has been reported to have promoted induction-frequency in
tobacco ovary culture (Wu and Chen
1982
).
