Agriculture Reference
In-Depth Information
4.6 Morus sp. (Family: Moraceae; Common name: Mulberry)
Mulberry is a vital crop for sericulture industry and is native to warm temperate
subtropical regions of Asia, Africa, Europe, and the Americas, with the majority
of the species native to Asia alone. Mulberry leaves are ecologically important as
the only food source for the silkworms (
Bombyx mori
), the pupa/cocoon which are
used to make silk. Apart from its application as a food source for the silkworms, the
medicinal properties of mulberry sp. are also widely acclaimed. Like many other
woody genera, mulberry is highly heterozygous and, therefore, production of hap-
loids and doubled haploids through anther culture is highly beneficial.
Several authors have reported androgenesis in mulberry which dealt with stud-
ies performed on induction of division in pollen culture (Katagiri
1989
), effects of
sugars and alcohols on pollen division (Katagiri and Modala
1991
), embryo differ-
entiation (Sethi et al.
1992
) and production of haploid plantlets from anther culture
(Shoukang et al.
1987
). However, detailed studies were conducted by Jain et al.
(
1996
) who evaluated the effect of temperature and Kinetin pre-treatment on induc-
tion of androgenic callus in anther cultures of mulberry. It was revealed that cold
pre-treatment given to flower buds at 4 °C for 24 h increased the percentage of cal-
lus originating from anther cultures. The anthers split and produced embryogenic
callus on Modified Bourgin (MB) medium (Qian et al.
1982
) with 8 % sucrose
and supplemented with NAA (2.68 µM) and BAP (4.44 µM). Upon transfer of the
calli to MB basal medium supplemented with NAA (2.68 µM), BAP (2.22 µM),
2,4-D (4.12 µM) and Polyvinyl pyrrolidone (PVP) (1.0 mg/l), embryos were in-
duced which later developed roots upon removal of 2, 4-D from the medium. Fi-
nally, the embryoids germinated precociously without developing cotyledons, but
forming elongated shoots. Rhizogenesis was induced when calli were subcultured
on MB medium containing NAA and BAP (each 0.5 mg/l with reduced myoinositol
(75 mg/l). The cytological study of the induced roots from the calli revealed the
haploid nature of the callus tissue.
To raise haploids from female clones of mulberry, ovary culture is the only pos-
sible approach because inbreeding and anther culture are not applicable (Thomas
et al.
1999
). In
ab initio
individual ovary cultures of
Morus alba,
the growth was
very poor and gynogenic plants were never formed, suggesting that unfertilized
ovaries required some stimulus from the parental tissue for the initial growth. This
is in contrast to the observations of Lakshmi Sita and Ravindran in 1991 who ob-
served gynogenesis in
ab initio
ovary cultures of
Morus indica
. These authors cul-
tured individual ovaries before or after fusion to form sorosis under field condi-
tions without taking any measure to prevent chance pollination. The inflorescence
of mulberry is a catkin in which ovaries are loosely arranged. After fertilization,
the ovaries enlarge and fuse to form a solid looking fruit called 'sorosis'. It was
possible that some of the ovaries cultured by them were fertilized. This could be
the reason that some of the gynogenic plants were haploid, others were diploid.
(Thomas et al. (
1999
) followed a two-step protocol for ovary culture of mulberry.
They raised nodal segment cultures on MS + BAP (5 µM) which developed axil-
