Marker-assisted backcrossing for disease resistance and agronomic traits in Carioca beans

Angular leaf spot, a disease caused by the fungus Pseudocercospora griseola, can lead to yield losses of up to 70% in the common bean (Phaseolus vulgaris) crop. Due to the quantitative character of angular leaf spot, a cultivar with high resistance depends on the presence of several resistance loci. In the present study, a marker-assisted backcrossing approach was used involving an Andean donor parent (AND 277) and a Mesoamerican recurrent parent (IAC-Milenio). For marker-assisted backcrossing in the BC1F1 genotypes, 15 molecular markers previously mapped for angular leaf spot resistance loci were used, and selection was performed by genotypes grouped with the donor parent in discrimination analysis of principal components. Through molecular selection, 42% of the BC2F3 families selected for the Carioca grain ideotype showed high resistance to angular leaf spot under controlled conditions of infection. Two lines resistant under natural conditions and tolerant to Fusarium wilt (Fusarium oxysporum f. sp. phaseoli J. B. Kendr. & W. C. Snyder) were selected for the competition trial. The lines selected, AM138 and AM167, showed superiority to the recurrent cultivar for six of the eight agronomic traits, including resistance to Race 65 of Colletotrichum lindemuthianum slow grain darkening, early maturity, and lighter grain color. Both advanced lines will be included in the value for cultivation and use trials; and as Carioca lines with resistance of Andean origin, they can be widely used as sources of resistance in breeding programs to overcome problems related to inter-gene pool crosses.

Automated summary

Marker-assisted backcrossing was used to develop two Carioca bean lines with high resistance to angular leaf spot, showing superior performance in other agronomic traits compared to the recurrent parent.