Comparison of resistant, tolerant, and susceptible host responses to Cherry Leaf Spot and assessment of trait inheritanc

Cherry Leaf Spot (CLS) is a devastating fungal disease of sour cherry where 'Montmorency', the major cultivar grown in the U.S., is highly susceptible. As many as 10 fungicide sprays can be required each growing season to combat this disease; therefore, developing CLS resistant cultivars is a top breeding priority. Past efforts identified cherry germplasm with resistance and tolerance to CLS; however, direct comparisons of the host disease responses had not been conducted. The goals of this study were to (i) compare CLS disease progression profiles of the susceptible 'Montmorency' and resistant and tolerant germplasm used in the MSU sour cherry breeding program, and (ii) gain an understanding of the inheritance of these traits by evaluating the host response of progeny individuals belonging to families derived from this germplasm. By observing host responses to CLS in a common environment with high disease pressure, significant differences were observed between the susceptible 'Montmorency' and the various tolerant and resistant selections in their response to CLS. These differences support previous reports that P. canescens derived resistance is consistent with a hypersensitive host response, and P. avium, P. cerasus 'North Star', and P. maackii derived tolerances are characterized by reduced infection and delayed defoliation compared to 'Montmorency'. Evaluation of the CLS host responses of progeny individuals derived from this germplasm supports a dominant two gene model for P. canescens derived resistance, and a recessive gene model for P. avium derived tolerance.