Basic HTML Version
Genomics and Applied Biology
23
Introduction
Cotton (
Gossypium
L.) is a leading fiber crop in the
world. Although the genus
Gossypium
L. has
approximately 50 species, only four of them are
cultivated, which include two diploids (2n = 2x = 26):
G. arboretum
L. (A2A2) and
G. herbaceum
L. (A1A1),
as well as two allotetraploids (2n = 4x = 52):
G.
Hirsutum
L. (AADD) and
G. barbadense
L. (AADD).
It was believed that the tetraploid cotton was
originated from an interspecific hybridization of an
old world diploid species that was closely related with
G. arboreum
or
G. herbaceum
(A genome donor) and a
new world diploid species relative to
G. raimondii
Ulbrich or
G. gossipioides
Standley (D genome donor),
which occurred about 1~2 million years ago (Beasley,
1940).
Use of heterosis in cotton production might be one of
the key approaches to increase seed cotton yield.
Heterosis for yield in F
1
hybrids cotton has been
extensively analyzed in the past decades. Useful
heterosis for yield in F
1
hybrids during 1947 and 1972
ranged from 7% to 50% in interspecific hybrids and
from 10% to 138% in intraspecific hybrids (Davis,
1978). In any hybrid programme, a large number of
crosses need to be made, while only few of the
hybrids will show good performance over the standard
check. This process is extremely labour intensive,
time-consuming and tedious. Molecular markers
increasingly detect locus differences among genotypes
and represent a powerful tool for the assessment of
genetic diversity in plant species (Tanksley, 1983).
Selection of desirable parents is an important task to
initiate a hybrid-breeding programme. Because
heterosis is associated with the interaction of different
alleles at a locus (Jones, 1945), it has been suggested
that molecular marker diversity may be used to select
parents for hybridization.
In cotton, a number of efforts have been made to
investigate the relationship between DNA marker-
based genotype variation of the parents to be used in a
hybrid- breeding programme and heterosis with
varying results. For example, Diers et al. (1996)
reported that marker- based genetic distance was not
consistently correlated with heterosis for inbred
diallels and for cultivar diallels in rape seed. Sheng et
al. (2002) reported significant correlation between
genetic distance and seed yield but the determinative
coefficient was very low (0.1024). However, Riaz et al.
(2001) found that the genetic distance of
sequence-related amplified polymorphism (SRAP) in
American.
B. napus
inbred lines was significantly
correlated with hybrid yield performance and heterosis.
Meredith and Brown (1998) studied the relationship
between genetic distance estimated by restriction
fragment length polymorphic (RFLP) markers among
15 cultivars and one strain from the USA and yield
heterosis of 120 F
2
hybrids produced by a half _
diallel genetic design and found that the correlation
were very low (r=0.08). Wu et al. (2002) studied the
correlation between genetic distance measured by
random amplified polymorphic DNAs (RAPD), inter
simple sequence repeat (ISSR) and simple sequence
repeat (SSR) markers among six domestic and two
exotic cultivars and interspecific F
1
and F
2
hybrids,
and found the correlation between these was low.
Gutierrez et al. (2002) used five US, four Australian
cultivars and two day- neutral converted lines of
G.hirsutum
to analysis the association between genetic
distance based on SSR markers and performance of
agronomic and fiber traits of F
2
-bulk populations and
deduced that significant correlations ranged from
negative to positive depending on the traits, genetic
background and environment.
Zhang et al. (2007) studied the relationship between
parental molecular marker diversity and hybrid
performance in both intra and inter specific hybrids of
cotton to evaluate the feasibility of predicting hybrid
performance using molecular markers. Three
cytoplasmic male sterile (CMS) lines were crossed
with 10 restorer lines to produce 22 F, hybrids during
2003. Of 22 F(1) s, 14 hybrids were intraspecific (
G.
hirsutum
×
G. hirsutum
) and eight interspecific (
G.
hirsutum
×
G. barbadense
). These 22 F, hybrids and
their parents were evaluated for yield and fiber quality
traits at Zhejiang University, Hangzhou, China during
2004 and 2005. Genetic distances (GD) among the
parents were calculated from 56 random-amplified
polymorphic DNAs (RAPD) and 66 simple sequence
repeat (SSR) marker data, and their correlation with
hybrid performance and heterosis were analysed.
Genomics and Applied Biology