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Fig. 15.9.
Segregant Bulk Analysis with the BAC33b SSCP-SNP primer. The sample order is: RP (resistant parent), SP
(susceptible parent), RB (resistant bulk), SB (susceptible bulk), and RecS-B (recombinant susceptible-bulk). The arrow points
to the polymorphic band.
database at CIAT with the Blastx algorithm
(Altschul et al. 1997); primers were designed
on each sequence selected, with expectation of
an amplification product of 300-350 pb, using
the Primer 3.0 software (Rozen and Skaletsky
2000). The amplification products were analyzed
as SSCP-SNP markers, following the protocol
explained previously. A clear difference between
resistant and susceptible individuals with the new
S-BAC33c SSCP-SNP marker that was consis-
tent in each individual of the bulk (opened bulk)
and without amplification in the recombinant
susceptible Bulk (RecS-B) was also obtained.
Selected BACs were again fingerprinted and
assembled into contigs; a new set of SSCP
markers were identified based on the BAC end-
sequence. Results of successive screenings led to
the identification of two markers, BAC33b and
SBAC33c, tightly linked to
CMD2
, at genetic
distance of 1 cM and 1.5 cM respectively. Addi-
tional screening of the BAC library with the
SBAC33c SSCP-SNP primer led to the construc-
tion of a BAC contig that stretches for about
500kb around
CMD2
. Toward final cloning of
the
CMD2
gene, the five BAC clones that tra-
verse a 500 kb region around the gene will be
sequenced and annotated to identify candidate R
genes.
Significance and Impact of MAB
for CMD Resistance
Breeders desire technologies that can lead
to improved utilization of genetic resources,
improved selection methods, improved produc-
tivity in targeted environments, and enhanced
potential for more rapid development of new cul-
tivars. MAB is quickly changing the structure
and operations of breeding programs in Africa,
Latin America, and Asia, as breeders introduce
MAS technology into their selection process.
Increasing numbers of breeders on the three con-
tinents are now rapidly integrating molecular
markers into their work, no longer considering
it an “add on” but, rather, an integral part of the
breeding process. Breeders in countries where
MAS is now being used are beginning to com-
bine both genetic and phenotypic selection to
maximize breeding effectiveness and efficiency.
In conventional breeding programs, the first
two to three years are devoted to screening
for CMD resistance before commencement of
Fig. 15.10.
Segregant Bulk Analysis using the S-BAC33c SSCP-SNP primer. The sample order is: RP (resistant parent),
SP (susceptible parent), RB (resistant bulk), SB (susceptible bulk), and RecS-B (recombinant susceptible-bulk). The arrow
points to the polymorphic band.
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