CYTOGENETICS:
Cytology:
Most of the species of Morus are diploid having 28 chromosomes, but a few
species like Moius tiliaefolia, M. cathyana and M. nigra are polyploids.
Genetic
improvement: Improved strains of mulberry are
obtained by adopting the conventional breeding methods followed in other
agricultural or horticultural plants.
Selection:
Mulberry is a highly heterozygous plant which is open for cross fertilization.
Therefore, the seeds that are formed through open pollination are natural
hybrids.
Method
of selection: Seeds collected from different plants
of different areas are planted in small seed bedsore in earthen pots. When they
attain a height of 15 or 30 cm they are transplanted in rows of 90 cm by 60 cm.
Characters
taken for selection:
1. The selected plant should be able to strike
roots when propagated through cuttings.
2. Greater and quicker percentage of sprouting
of vegetative bends.
3. Height of the plant.
4. Branching habit.
5. Shortest internodes length.
6. Shape and size of the lamina.
7. Succulence of leaf.
8.
Palatability to silkworms.
9.
Leaf yield per unit area.
10.
Response to indigenous cultural practices.
Hybridization
and selection: The
purpose of breeding mulberry is to develop or evolve varieties that are
efficient in nutrients that give the greatest return of high quality leaf per
unit area.
Techniques
of hybridization: The technique of hybridization mainly
consists of processes to ensure the pollen and stigma of known plants being
brought together.
BREEDING:
Appliances
necessary for breeding
1. Hand lens.
2. Small camel hair brush.
3. Fine pointed or curved scissors.
4. Cellophane paper covers or bags to cover
the male and female catkins.
5. Specimen tubes and Petri dishes to collect
and store the pollen from male flowers.
6. Mounted needles.
7. Stakes and field labels for marking the
selected parents.
8. Field labels for marking the crossed
flowers.
9. Field stool.
10. Field records.
11. Refrigerator to store the pollen.
Collection
and maintenance of Germplasm: The starting point of any breeding program is
the collection of as many varieties of mulberry as possible both exotic and
indigenous, cultivated and wild, followed by the evaluation of the material for
desirable characters.
Selection
of parents: Based on the above studies, male and female parents ire to
be selected. The hybridization work may be carried out on branches of grown up
trees.
Anthesis:
A detailed study of either parent is made so as to find out when another sac
burst open, viability period of pollen, etc. in the male catkin and the receptivity
of the stigma in the female flower.
Collection
of pollen: When the male flowers bloom, pollen is
collected from them with the help of a small camel hair brush, into small
specimen tubes.
Artificial
pollination: The pollen thus collected from the
male flower is dusted on the stigmatic surface of the female flowers by
removing the cellophane bags and covering them again after dusting till the
stigma is no more receptive or has lost its function.
Breeding
for disease resistance: Mulberry, as any other
commercial crop, is susceptible to the attack of various pathogens causing
damage to the plantations. Powdery mildew disease cause by Phyllactenia
corylea especially during rainy seasons is a problem to be solved at higher
altitudes.
Breeding
for drought resistance: Resistance to drought conditions
is an important character to be associated with other desirable characters in
tropical and semi‑arid regions.
Polyploidy
Breeding: Majority of the species of mulberry are diploids. However,
certain species like Morus nigra and Morus cathyana are polyploids. Polyploidy
in mulberry, either natural or artificial, has a great economic value in the
evolution of superior strains.
Treatment
with colchicines: Seeds, seedlings and vegetative buds
are used for colchicines treatment. The chemical can be applied adopting any of
the methods given below:
1.
Twigs are immersed with colchicines solution of various concentrations for
different durations.
2.
Solutions of colchicines in agar‑agar may be applied to growing buds: the
solution is warmed in a liquid state before application.
3.
The colchicines solution is allowed to fall on the growing bud at proper
intervals.
4.
The chemical may be applied as a paste in lanolin.
5.
Germinating seeds may be soaked in colchicines solution of varying
concentrations for varying durations.
Mutation
Breeding: Since mulberry is a highly heterozygous plant there is
great scope to introduce variability through conventional breeding methods.
Inducing mutations artificially might also be beneficial to eliminate certain
undesirable characters.
Characters
of mutation:
1.
Mutations differ from the parental type in one or more of morphological,
physiological or biochemical traits.
2.
Most of the mutations are recessive and they are carried along in heterozygous
condition for several generations, being a cross fertilized plant.
3. Different mutations at the same races give
rise to the multiple allelic series.
4. Any particular change in the gene is
usually recurrent.
5. Mutations are often reversible.
Chemical
mutagenesis in mulberry: Beneficial mutants are also
obtained in mulberry with the application of various mutagenic chemicals.
Mutagenic
chemicals
1. Ethyl Methane Sulphonate (E.M.S.)
2. Methyl Methane Sulphonate (M.M.S.)
3. 1‑4 Dimethyl sulphonoxy butane
4. Diethyl sulphate
5. Malic hydrazide
6. 8‑Ethoxy‑caffine
7. 5‑Bromo Uracil
8. Hydroxylamine.
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