Using molecular markers to pyramid genes for resistance to ascochyta blight and anthracnose in lentil (Lens culinaris Medik)

Ascochyta blight caused by the fungus Ascochyta lentis Vassilievsky and anthracnose caused by Colletotrichum truncatum [(Schwein.) Andrus & W. D. Moore] are the most destructive diseases of lentil in Canada. The diseases reduce both seed yield and seed quality. Previous studies demonstrated that two genes, ral1 and AbR1, confer resistance to A. lentis and a major gene controls the resistance to 95B36 isolate of C. truncatum. Molecular markers linked to each gene have been identified. The current study was conducted to pyramid the two genes for resistance to ascochyta blight and the gene for resistance to anthracnose into lentil breeding lines. A population (F-6:7) consisting of 156 recombinant inbred lines (RILs) was developed from a cross between 'CDC Robin' and a breeding line '964a-46'. The RILs were screened for reaction to two isolates (A1 and 3D2) of A. lentis and one isolate (95B36) of C. truncatum. chi(2) analysis of disease reactions demonstrated that the observed segregation ratios of resistant versus susceptible fit the two gene model for resistance to ascochyta blight and a single gene model for resistance to anthracnose. Using markers linked to ral1 (UBC227(1290)), to AbR1 (RB18(680)) and to the major gene for resistance to anthracnose (OPO6(1250)), respectively, we confirmed that 11 RILs retained all the three resistance genes. More than 82% of the lines that had either or both RB18680 and UBC227(1290) markers were resistant to 3D2 isolate and had a mean disease score lower than 2.5. By contrast, 80% of the lines that had none of the RAPD markers were susceptible and had a mean disease score of 5.8. For the case of A1 isolate of A. lentis, more than 74% of the lines that carried UBC227(1290) were resistant, whereas more than 79% of the lines that do not have the marker were susceptible. The analysis of the RILs using OPO6(1250) marker demonstrated that 11 out of 72 resistant lines carried the marker, whereas 66 out of 84 susceptible lines had the marker present. Therefore, selecting materials with both markers for resistance to ascochyta blight and a marker for resistance to anthracnose can clearly make progress toward resistance in the population.