Biology Reference
In-Depth Information
Despite these constraints, classical breeding tools were helpful in genetically
enhancing palms for productivity, disease resistance, and so on. Some successful
case studies are given below.
Coconut palms grow very tall and reach a height of 10-20 m, making harvest fea-
sible only with the help of laborers skilled in climbing. Dwarf trait is spontaneously
noticed in coconut at relatively very low frequencies. Hybrids involving dwarf and
tall forms of coconut offer promise in breeding for intermediate height, early bear-
ing, and high yield. Lethal yellowing is a major phytoplasma disease killing millions
of coconut palms in Latin American and Caribbean countries. Coconut germplasm
available in these countries does not offer resistance to the malady. Cross-breeding
Malayan dwarf coconut varieties from Malaysia, with local talls helped to produce
more resistant strains
[10]
.
Dura and pisifera are two common forms of oil palm. Dura has a thick-shelled kernel,
whereas pisifera is a thin-shelled kernel type. Tenera is a high-yielding hybrid, a cross
between dura and pisifera oil palms, differing in shell thickness (
Sh
), a trait controlled
by a single dominant gene
[11]
. Mutation breeding has been attempted in date palm to
induce resistance to Bayoud disease
[12]
. Spontaneous mutants are utilized in coconut
palm for jelly-like endosperm
[13]
controlled by a single recessive gene.
Chromosome numbers in most palms vary from 2
n
26 to 36. Polyploidy is uncom-
mon among the palms except the four species
Arenga caudata
(2
n
4
x
64),
Rhapis
humilis
(2
n
4
x
72),
Jubaeopsis caffra
(2
n
12
x
160-200), and
Voanioala gerar-
dii
(
V. gerardii
[Arecoideae]) with 2
n
~600. Polyploidy is induced in oil palm, using
chemical treatments of colchicine and oryzalin treatments
[14]
. Androgenic haploids are
induced in coconut, using an
in vitro
culture of pollen
[15]
. DNA content, also known
as
C
-value in a species, is measured using flow cytometry technique and is expressed in
picograms.
C
-value is known for 104 species of palms as of date and varies from 0.25 pg
in cultivated date palm (
Phoenix dactlyfera
) to 39 pg in
V. gerardii
, with a mean value of
4.04 pg
[16]
. Karyological data of 56 palm taxa revealed that the chromosome number
ranged from 2
n
36 in ancestral species to 2
n
26 as dysploid series in different sub-
families (
Figure 1.1
). Strong deviations in vegetative and floral morphology are accom-
panied by karyological differences
[17]
. Polyploidy is artificially induced in oil palm,
Minimum
Maximum
36
36
34
36
28
26
26
28
Figure 1.1
Range of chromosome numbers (2
n
) in subfamilies (Roser
[17]
).
