Genetic variation and association mapping of aphid (Macrosiphoniella sanbourni) resistance in chrysanthemum (Chrysanthemum morifolium Ramat.)

Aphid, Macrosiphoniella sanbourni, is a major insect pest that adversely affects ornamental quality and production of chrysanthemum, thus it is critical to develop new cultivars resistant to aphid. However, the genetic mechanism governing aphid resistance is thus far not thoroughly investigated in chrysanthemum. This study aimed to characterize the genetic variation of the aphid resistance in a global collection of 80 chrysanthemum entries, during summer and autumn under greenhouse condition, and to identify the molecular markers for aphid resistance by association mapping. The performances of aphid resistance, quantified by the average damage index of aphid, was significantly correlated (r = 0.93, P<0.01) between two seasons. The coefficients phenotypic and genetic variation was calculated around 26-27%; and a high magnitude (0.93) of broad-sense heritability, together with a moderate relative genetic advance (similar to 68%), was estimated for aphid resistance. By using the MLM model that integrates population structure and kinship matrix as covariates association mapping identified 11 markers related to aphid resistance, with the individually explained phenotypic variation ranging from similar to 11 to similar to 57%. Of the three markers predicted in both seasons, SSR184-1 and E1M5-1were identified as favorable alleles for aphid resistance. Seven cultivars harboring the two favorable alleles were identified as potential donor parents for future improvement of resistance against aphid. These findings add further understanding of the genetic determination of aphid resistance, and the identified favorable alleles and donor parents open a possibility to produce chrysanthemums with enhanced aphid resistance in future.