Emerging citrus diseases in Europe caused by species of Diaporthe

Abstract

Species of Diaporthe are considered important plant pathogens, saprobes, and endophytes on a wide range of plant hosts. Several species are well-known on citrus, either as agents of pre- or post-harvest infections, such as dieback, melanose and stem-end rot on fruit. In this study we explored the occurrence, diversity and pathogenicity of Diaporthe species associated with Citrus and allied genera in European orchards, nurseries, and gardens. Surveys were carried out during 2015 and 2016 in Greece, Italy, Malta, Portugal, and Spain. A total of 79 Diaporthe strains were isolated from symptomatic twigs, branches and trunks. A multi-locus phylogeny was established based on five genomic loci (ITS, tef1, cal, his3 and tub2), and the morphological characters of the isolates determined. Preliminary pathogenicity tests were performed on lemon, lime, and orange plants with representative isolates. The most commonly isolated species were D. foeniculina and D. baccae, while only four isolates of D. novem were collected. Two new Diaporthe species, described here as D. limonicola and D. melitensis spp. nov. were found associated with a new devastating dieback disease of lemon plants. Furthermore, one cluster of sterile Diaporthe isolates was renamed as D. infertilis. Pathogenicity tests revealed most of the Citrus species as susceptible to D. baccae, D. foeniculina, and D. novem. Moreover, D. limonicola and D. melitensis caused serious cankers affecting all the Citrus species tested. This study is the first report of D. baccae and D. novem on citrus in Europe, and the first detection of a new Diaporthe canker disease of citrus in Europe. However, no isolates of D. citri were found. The study improves our understanding of the species associated with several disease symptoms on citrus plants, and provides useful information for effective disease management.

High diversity of Diaporthe species associated with dieback diseases in China, with twelve new species described

“…Thus, during the past decade, a polyphasic approach, employing multi-locus DNA data together with morphology and ecology, has been employed for species boundaries in the genus (Crous et al 2012, Udayanga et al 2014a, b, Huang et al 2015, Gao et al 2016, 2017, Guarnaccia and Crous 2017, 2018, Hyde et al 2017, 2018, Yang et al 2017a, b, 2018, Guarnaccia et al 2018, Jayawardena et al 2018, Perera et al 2018a, b, Tibpromma et al 2018, Wanasinghe et al 2018). …”

“…The genus Diaporthe Nitschke represents a cosmopolitan group of fungi occupying diverse ecological behaviour as plant pathogens, endophytes and saprobes (Muralli et al 2006, Rossman et al 2007, Garcia-Reyne et al 2011, Udayanga et al 2011, 2012a, b, 2014a, b, 2015, Gomes et al 2013, Fan et al 2015, Du et al 2016, Dissanayake et al 2017b, Guarnaccia and Crous 2017, Yang et al 2017a, b, 2018, Guarnaccia et al 2018, Marin-Felix et al 2018). Diaporthe species are responsible for diseases on a wide range of plant hosts, including agricultural crops, forest trees and ornamentals, some of which are economically important.…”

“…Diaporthecitri is another well-known pathogen exclusively found on Citrus spp. causing melanose, stem-end rot and gummosis in all the citrus production areas except Europe (Mondal et al 2007, Udayanga et al 2014a, Guarnaccia and Crous 2017, 2018). Similarly, stem canker, attributed to several Diaporthe spp., is one of the most important diseases of sunflower ( Helianthusannuus ) worldwide (Muntañola-Cvetković et al 1981, Thompson et al 2011).…”

“…Species identification is essential for understanding the epidemiology and plant diseases management and to guide the implementation of phytosanitary measures (Santos and Phillips 2009, Udayanga et al 2011, Santos et al 2017). Thus, molecular data are necessary to resolve Diaporthe taxonomy and, during the recent years, many species have been described through a polyphasic approach together with morphology (Gomes et al 2013, Udayanga et al 2014a, b, 2015, Huang et al 2015, Gao et al 2017, Guarnaccia and Crous 2017, Yang et al 2018). Santos et al (2017) revealed that the use of a five-loci dataset (ITS- cal - his3 - tef1 - tub2 ) is the optimal combination for species delimitation, showing the ribosomal ITS locus as the least informative, which is contrary to the result of Santos et al (2010).…”

“…Although the classification of Diaporthe has been on-going, species are currently being identified based on a combination of morphological, cultural, phytopathological and phylogenetical analyses (Gomes et al 2013, Huang et al 2013, 2015, Udayanga et al 2014a, b, 2015, Fan et al 2015, Du et al 2016, Gao et al 2016, 2017, Guarnaccia and Crous 2017, Hyde et al 2017, 2018, Guarnaccia et al 2018, Jayawardena et al 2018, Perera et al 2018a, b, Tibpromma et al 2018, Wanasinghe et al 2018). However, fungi isolated from forest trees in China were recorded in old fungal literature without any living culture and molecular data (Teng 1963, Tai 1979, Wei 1979).…”