Executive Summary
We made
significant progress in determining allelic relationship between ALS
resistance genes, identifying molecular markers linked to these genes
and developing protocols for the use of these markers in MAS. We showed
that resistance genes in three sources of resistance (G10909, G10474 and
Mexico 54) that have been found to be effective against a wide range of
the ALS pathotypes segregate independently, thus are probably carried on
different loci. Therefore these genes can be put into the same
background to provide resistance to a wide range of angular leaf spot
pathotypes. Molecular markers linked to genes in these three sources of
resistance were successfully converted to SCAR markers. The PF13 and
SCAR maker is codominant and can only be used to introgress G10909
resistance genes into Andean backgrounds. A RAPD derived SCAR marker
OPE4709 was shown to be useful for selecting the Mexico
54 gene in an Andean background. In addition, this marker was mapped to
the distal end of linkage group B08. Three SCAR markers (PF 11,
PF9 260G1, and OPE4709) were
successfully developed for Mexico 54, G10474, G10909 and respectively.
Parental surveys carried out using the PF9 260G1 SCAR marker
revealed its utility to introgress the G10474 gene into both Andean and
Mesoamerican bean backgrounds.
Protocols for the
use of marker linked to anthracnose (Co-42,
and Co-5) and bean common mosaic virus (ROC 11) were
developed. These markers were optimized for use with DNA extracted using
the alkaline miniprep method. The advantage of this DNA extraction
method is that large samples (96) can be processed in less than 30
minutes, making this method ideal for massive marker assisted selection.
A mechanism to
enable bean network partners in different countries to make use of MAS
was initiated successfully by two national programs (Rwanda and Uganda)
in screening some of the advanced lines for presence of the resistance
gene against ALS. A SCAR marker OPE4709 previously converted
from a RAPD marker and linked to the resistance in Mex 54 was used. It
was observed to be present in 60% of 26 advanced lines from Rwanda and
13% of the 75 advanced lines from Uganda. The next stage is to have
participation of more partners and assess different procedural
options.
Previous studies identified RWR719 as a good source of resistance to
Pythium root rots and this genotype is currently being used in programs
to introgress resistance to Pythium root rot into
commercial varieties in Eastern Africa. We identified five (for the
first time) markers that segregated in coupling phase to the Pythium
resistance gene in RWR 719. Two of these markers (OPAA19, OPBA08)
were successfully converted to SCAR markers. Testing of resistant and
susceptible genotypes showed that these markers were present in all
resistant and absent in all susceptible genotypes, showing the potential
utility of these markers for MAS.
The
utility of locus-specific microsatellite markers developed for
Phasoisariopsis griseola, the causal agent of the bean angular leaf
spot disease was tested on a world wide collection that consists of 808
isolates.
Preliminary results confirmed the two lineages of the pathogen, Andean
and Mesoamerican that are associated with common bean gene pools.
Further analysis revealed that within each group, isolates from Africa
were distinct from isolates originating from the rest of the world,
signifying that probably Africa might be a center of diversification of
beans. Further analysis of the data, including development of race
structure maps is underway.
Segregating
populations generated from crosses designed to improve deficiencies in a
major commercial variety in Tanzania, Lyamungu 85, by the regional
breeding programme in Kenya continued to be selected. Several F2.4,
F2.5 and F2.6 and F1-derived
lines with resistance to two or more diseases under field conditions
were identified. In Uganda, 112 lines with red mottled grain type were
selected for testing in preliminary yield trials.
In Uganda,
several progenies were selected from 2 sites from several F2
derived F4, F5, and F6 lines. A total
of 139 progenies were selected from over 500 recombinant inbred lines (RILs)
and a backcross program to developed resistance to Pythium root rots.
Of 196 F6 progenies derived from crosses to combine
resistance to Pythium and ALS, 85 were resistant and 65% of these were
of the preferred Calima seed types. Some of these populations are being
evaluated in Uganda, Rwanda, Kenya, Malawi and South Africa, and
Tanzania.
Several lines
have been found to be tolerant or partially resistant to Fusarium root
rot (Fusarium solani fsp. phaseoli) from over a collection
of 160 lines that included, Ugandan land races, lines from CIAT-Colombia,
Pythium root rot nursery and South Africa). Several populations have
been developed from MLB-49-89A, MLB-48-89A, RWR 719, Umgeni, G 4795,
G1459, K132, K20 and Kanyebwa for the development of market class
varieties in Uganda resistant to Fusarium root rot. Populations are at
F1 and F2 stages.
Allan Male Mwalye
received training at CIAT HQ on use of molecular methods in pathogen
diagnosis and marker assisted selection). Support is ongoing for
one PhD student at the University of KwaZulu Natal who is doing her
thesis research at Kawanda. A student from
Uganda has been identified for support under the project and will be
registering Makerere this year for a PhD study program.
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