Reaction of Mandarins to the Alternaria Brown Spot and Huanglongbing: Identification of Potential Varieties for These Diseases to Be Managed in the Field

Mandarins occupy the third group among citrus produced in Brazil. Primarily aimed at the fresh fruit market, commercial orchards have suffered significant production losses due to the high incidence of diseases, such as the alternaria brown spot (ABS) and huanglongbing (HLB). The fact that 80% of the orchards are composed of two varieties, Ponkan mandarin and Murcott tangor, which are highly susceptible to both diseases, demands intensive chemical control of the diseases in the field, which has resulted in a significant increase in production costs and a negative environmental impact. A total of one hundred and seventy-three mandarin accessions, including several species and hybrids belonging to the Collections of the Instituto Agronomico de Campinas (IAC), were evaluated in the field in an endemic location for the diseases. Evaluations of the incidence and severity of the diseases showed a range of genotypes tolerant to ABS that could replace the current commercial varieties, mainly within the clementine and willow leaf mandarin groups. Although, with differences in incidence and susceptibility to HLB, there are no tolerant varieties to this disease, which significantly impacts the loss of fruit quality.