Co-segregation of resistance genes to Colletotrichum lindemuthianum and Pseudocercospora griseola in common bean recombinant inbred lines

Anthracnose and angular leaf spot, caused by Colletotrichum lindemuthianum and Pseudocercospora griseola, respectively, are among the most destructive diseases affecting common bean (Phaseolus vulgaris L.) worldwide, leading to severe yield losses and posing major challenges to breeding programs due to the high variability of pathogen populations. The identification of resistance loci and their genetic relationships is essential for the development of cultivars with durable and broad-spectrum resistance. In this study, we investigated the inheritance and co-segregation of resistance to race 73 of C. lindemuthianum and race 63-39 of P. griseola using 56 F2:8 recombinant inbred lines derived from the cross between Awauna UEM (resistant) and IPR88 Uirapuru (susceptible). Phenotypic evaluations revealed clear segregation patterns for both diseases, fitting a 1:1 ratio, consistent with monogenic inheritance. Resistance to anthracnose was associated with the Co-4² allele, while resistance to angular leaf spot was controlled by a major locus herein designated as PhgPv08AW. The observed segregation fitted the expected 1RR:1SS ratio, with a χ² value of 0.071 and a P-value of 0.78, indicating monogenic dominant resistance to race 73 of C. lindemuthianum. Similarly, segregation for race 63-39 of P. griseola also fitted the 1RR:1SS ratio (χ² = 0.64 and P = 0.42). Co-segregation analysis showed that 50 out of 56 lines exhibited identical resistance responses to both pathogens, with only six recombinant lines, indicating tight genetic linkage between Co-4² and PhgPv08AW. These results suggest that resistance to both diseases is controlled by closely linked loci, likely located within a resistance gene cluster. From a breeding perspective, the co-segregation of resistance to two major diseases represents a highly advantageous genetic configuration, enabling simultaneous selection and facilitating gene pyramiding strategies. Overall, this study provides new insights into the genetic architecture of disease resistance in common bean and highlights the potential of exploiting linked resistance loci to accelerate the development of cultivars with durable and broad-spectrum resistance.