Contents - Faperta

180 Biotechnological Approaches for Pest Management and Ecological Sustainability
Cowpea
The development of RFLP map of cowpea has allowed the investigation of association
between genes of interest (Fatokun et al., 1992; Young et al., 1992a, 1992b; Myers, Fatokun,
and Young, 1996; Fatokun, Young, and Myers, 1997; Menendez, Hall, and Gepts, 1997). A
cross between an aphid, A. craccivora-resistant cultivated cowpea, IT 84S-2246-4, and aphidsusceptible
wild cowpea, NI 963, has been evaluated for aphid resistance and RFLP marker
segregation (Myers, Fatokun, and Young, 1996). One RFLP marker, bg4D9b, has been found
to be tightly linked to aphid resistance gene (Rac1), and several fl anking markers in the
same linkage group (linkage group 1) were also identifi ed. The close association of Rac1
and bg4D9b presents an opportunity for cloning this insect resistance gene. Githiri, Kimani,
and Pathak (1996) studied the linkage of aphid resistance gene, Rac with various polymorphic
loci controlling morphological traits and aspartate amino-transferase isozyme (AAT)
to identify simply inherited and easily identifi able markers for aphid resistance, and to
distinguish between Rac1 and Rac2. The F2 and F2-derived F3 populations from crosses IT
87S-1459 TVu 946 ICV 5 and IT 84S-2246 TVu 946 segregating for Rac1, and the cross
ICV 12 TVu 946 segregating for Rac2 have been evaluated for various polymorphic morphological
traits. Locus pd, controlling peduncle color, was found to be linked to both Rac1
and Rac2. The recombination frequencies estimated by the maximum likelihood method
were 26% ± 8.3% and 35% ± 7.5% for Rac1-pd and Rac2-pd co-segregation, respectively, indicating
that Rac1 and Rac2 were not different from one another. No linkage was detected between
aphid resistance genes and the genes controlling morphological traits or AAT isozyme.
Common Bean
A genetic linkage map of common bean for agronomic traits has been developed by Tar’an,
Michaels, and Pauls (2002). Schneider, Brothers, and Kelley (1997) used seven markers for
MAS, and improved yield under stress conditions by 11%. Common bean near-isogenic
lines differing for the recessive bean common mosaic virus (BCMV) resistance allele bc-3
have been screened to identify RAPD markers linked to BCMV (Haley, Afanador, and
Kelly, 1994). Categorization of the bc-3 genotypes in the F 2 population revealed that selection
against the repulsion-phase RAPD, as opposed to selection for the coupling-phase
RAPD, provided a greater proportion of homozygous resistant selections (81.8% versus
26.3%), and a lower proportion of both segregating (18.2% versus 72.5%) and homozygous
susceptible (0.0% versus 1.2%) selections. Selection of individual plants based on phenotype
of both RAPD markers was identical to selection based solely on the repulsion-phase
RAPD alone. Bulk segregant analysis and quantitative trait analysis identifi ed eight markers
associated with resistance to potato leafhopper, E. fabae, and four markers that were
associated with resistance to E. kraemeri Ross and Moore (Murray et al., 2004). Three markers
were associated with resistance to both species. Composite interval mapping identifi ed
QTL for resistance to the leafhopper on core-map linkage groups B1, B3, and B7. QTL for
seed weight were close to the locus controlling testa color and the phaseolin gene.
Mesoamerican bean lines BAT 881 and G 21212 showed transgressive segregation for
resistance to thrips, Thrips palmi Karny, in the fi eld. Correlations between damage and
reproductive adaptation scores were signifi cant within and between seasons (Frei et al.,
2005). A major QTL (Tpr6.1) for thrips resistance located on LG b06 explained up to
26.8% of variance for resistance in a single season. Joint interval mapping across seasons
revealed various QTLs on LGs b02, b03, b06, and b08, some of which were located in regions
containing genes encoding for disease resistance.