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 (OPNO2_890C) 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  OPNO2_890C SCAR in the F₂  populations  and determine if it can be used in selecting resistant genotypes.