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Plant Breeding Home
Inheritance
of angular leaf spot resistance and marker assisted selection for
disease resistance in common bean
A. Namayanja, R. Buruchara, P. Kimani, G. Mahuku & P. Rubaihayo
Research Abstract
Angular leaf spot (ALS) caused by
Phaeoisariopsis griseola (Sacc.) Ferr. is one of the major diseases
affecting the common bean (Phaseolus
vulgaris)
world wide. In
Africa, it is the most
prevalent and economically
important disease of beans. It is particularly important in Malawi,
Ethiopia, Kenya, Uganda, Tanzania, Rwanda, Burundi and in the Kivu
province of Congo. In
Uganda, most of the released varieties and popular land races succumb
angular leaf spot, with yield losses of up to 55%. Breeding for
resistance is the most effective control strategy, since beans are grown
mostly by small scale farmers for whom alternative control measures are
not practical. Several sources of resistance have been identified.
Unfortunately the nature of resistance genes has not been fully
characterized. A study was
initiated at Namulonge Research Station and at Kawanda Research Station
to: (1) characterize the resistance to ALS in the cultivar Mexico 54;
(2) determine if the SCAR marker (OPNO2890C) linked to the
resistance gene phg-2 present
in Mexico 54 is useful in populations other than the one from which it
was identified; and, (3) to introduce resistance to some of the popular
but susceptible varieties. Crosses were made between Mexico 54 and three
susceptible cultivars: K131, K 132 (released varieties in Uganda) and a
popular land race, Kanyebwa. A portion of the resulting F1
seeds was used to generate the F2 and backcross populations
to each of the susceptible cultivars and to the resistant parent. The F1,
F2 and backcross progenies and their parents were inoculated
with P. griseola Mesoamerican
race 2A in a screenhouse.
The plants were visually evaluated for disease severity using the
1 to 9 CIAT scale. F2
progenies of crosses with Mexico 54, showed a segregation ratio of
resistant to susceptible of 3:1.
A resistant to susceptible ratio of 1:1 was observed among the backcross
progeny to the susceptible parents.
Backcross progeny to the resistant parent were resistant. This
indicated that a single dominant gene conditions
resistance to P.griseola
race 2A in Mexico 54. Activities are underway to detect the
OPNO2890C SCAR in the F2 populations and
determine if it can be used in selecting resistant genotypes.
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