Phyllosticta capitalensis and P. paracapitalensis are endophytic fungi that show potential to inhibit pathogenic P. citricarpa on citrus

Abstract

Citrus black spot (Phyllosticta citricarpa) is an economically important disease of citrus in Australia. A closely related endophyte, P. capitalensis, also occurs on citrus in Australia, and the two fungi are known to co-exist in orchards. The diversity of other species of Phyllosticta on Citrus in Australia is unknown. Citrus black spot is managed by fungicide treatment and options such as biological control may be better economic alternatives. We studied the diversity of Phyllosticta on Citrus in Australia with a phylogenetic species hypothesis. We report P. paracapitalensis for the first time and confirm the presence of P. capitalensis in Queensland. Many examined isolates of Phyllosticta previously identified as P. capitalensis were reidentified as P. paracapitalensis. We also provide evidence through Koch’s postulates that the two endophytic species are non-pathogenic on citrus fruit. In addition, disease incidence and severity of citrus black spot was significantly reduced when fruit were pre-inoculated with one of the endophytes 14 days prior to pathogen inoculation on the same fruit. Our results indicate these endophytes may have potential antagonistic effects against P. citricarpa under field conditions.