Agriculture Reference
In-Depth Information
on many legumes and woody plants as they are rather recalcitrant (Sangwan-Norreel
et al.
1986
; Bajaj
1990
; Raghavan
1990
; Wenzel et al.
1995
; Germanà
2006
,
2009
,
2011
). Recent advances in anther culture have been reported by Dunwell (
2010
),
Wedzony et al. (
2009
), Pratap et al. (
2009
), Srivastava and Chaturvedi (
2008
); and
Touraev et al. (
2009
). Unfertilized ovary-ovule culture has been applied to species
including sugar beet, tulip, cucumber, sweet potato, onion, squash, gerbera, rice,
maize, niger and tea (Chen et al.
2011
). Wide hybridization method for production
of haploids is routinely used in wheat and other cereal breeding programmes. The
general method followed involves a phase of embryo rescue in vitro, usually fol-
lowed by chromosome doubling with colchicine (Maluszynski et al.
2003a
).
1.4 Efficiency of Haploid Production
Homozygous lines are of utmost importance in breeding programmes. Wide hy-
bridization and anther/microspore culture are two of the most preferred techniques
for doubled haploid production in crop plants. There is not much difference in the
cost of haploid production or in the time and amount of labour required to produce
haploids via these means. Currently, gynogenesis is the least favoured technique
because of the low efficiency of production of haploids, but the value of doubled
haploids in species that do not respond to other methods of haploid production
makes this method worthwhile (Maluszynski et al.
2003a
; Touraev et al.
2001
).
The limitation of wide hybridization is that it is restricted to the cereals where
the chromosome elimination system appears to operate. Each crop has different
requirements and, thus, there is need for extensive research to develop an efficient
system. Wide hybridization has the advantage of being quite effective across geno-
types and produces little or no induced variation from cultured embryos. How-
ever, anther/microspore culture scores higher over distant hybridization due to
the fact that anthers harbour large numbers of haploid microspores per anther. In
barley and wheat, where both systems have been comparatively well developed,
the yield of green plants from isolated microspore culture can be up to 100 times
higher than from wide hybridization in the most responsive genotypes (Kasha and
Maluszynski
2003
).
Anther culture is feasible in most species but it generally takes plenty of time
to develop a competent system in some crops. Moreover, a good aseptic tech-
nique is a necessity even though the available methods are simple and reproduc-
ible (Maluszynski et al.
2003a
). In general, haploid plants are regenerated in vitro
from the microspores contained in the anther and require chromosome doubling
treatments using chemicals such as colchicine, pronamide, trifluralin, oryzalin and
amiprophos methyl (APM) (Wan et al.
1991
). A few species such as barley regener-
ate a large number of doubled haploids as a result of induced chromosome doubling
during early division of the microspores (Kasha
2005
). Although the application of
anther culture is widespread, the presence of the sporophytic anther wall serves as
