Resistance and susceptibility of mandarins and their hybrids to Alternaria alternata

Abstract

Caused by Alternaria alternata, Alternaria brown spot (ABS) is a major fungal disease of mandarins in Brazil, causing serious losses in commercial orchards of Ponkan tangerine (Citrus reticulata Blanco) and Murcott tangor [C. sinensis (L.) Osbeck × C. reticulata Blanco]. The response of 31 accessions/genotypes of mandarins and their hybrids to A. alternata, was evaluated in São Paulo state, Brazil. The incidence and severity of the disease in fruit were evaluated in the field, using diagrammatic scale, four times during 2008 and 2009. Based on these data, the area under the disease progress curve (AUDPC) was calculated. In parallel, in vivo and in vitro inoculations with A. alternata were made on leaves to confirm field results. Resistance and susceptibility was evaluated in controlled experiments by counting the number of lesions per leaf using a diagrammatic scale. Most of the genotypes were symptomatic after inoculation with A. alternata with disease most severe on the hybrids Nova, África do Sul, Ponkan and Murcott. Cultivars like Cravo, Nules and Ortanique that have excellent fruit quality and had lower AUDPCs, whereas Fremont and Thomas were highly resistant to the fungus and did not show any symptoms in the field or in controlled inoculations. The attractiveness and pronounced flavor of Fremont and Thomas fruit make them new options for the citriculture.