Pathotypes and Genetic Relationship of Worldwide Collections of Elsinoë spp. Causing Scab Diseases of Citrus

Abstract

Two scab diseases are recognized currently on citrus: citrus scab, caused by Elsinoë fawcettii, and sweet orange scab, caused by E. australis. Because the two species cannot be reliably distinguished by morphological or cultural characteristics, host range and molecular methods must be used to identify isolates. Four pathotypes of E. fawcettii and two of E. australis have been described to date based on host range. The host specificity and genetic relationships among 76 isolates from Argentina, Australia, Brazil, Korea, New Zealand, and the United States were investigated. Based on pathogenicity tests on eight differential hosts, 61 isolates were identified as E. fawcettii and 15 as E. australis. Of 61 isolates of E. fawcettii, 24 isolates were identified as the Florida broad host range (FBHR) pathotype, 7 as the Florida narrow host range (FNHR) pathotype, 10 as the Tryon's pathotype, and 3 as the "Lemon" pathotype. Two new pathotypes, the "Jingeul" and the satsuma, rough lemon, grape-fruit, clementine (SRGC), are described, and four isolates did not fit into any of the known pathotypes of E. fawcettii. Of the 15 isolates of E. australis from Argentina and Brazil, 9 belonged to the sweet orange pathotype and 6 from Korea to the natsudaidai pathotype. E. fawcettii and E. australis were clearly distinguishable among groups by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) assays and the E. fawcettii group was divided into three subgroups, A-1, A-2, and A-3. The A-1 group was composed of the FBHR, FNHR, and SRGC pathotypes; some Lemon pathotypes; and the uncertain isolates. The A-2 subgroup included all of the Tryon's pathotype isolates and one of the three Lemon pathotype isolates and the A-3 group contained the Jingeul pathotype isolates. E. australis was differentiated into two groups: B-1, the natsudaidai pathotype isolates, and B-2, the sweet orange pathotype isolates. Isolates of E. fawcettii and E. australis were clearly distinguishable by sequence analysis of the internal transcribed spacer (ITS) region and the translation elongation factor 1 alpha (TEF) gene. There were also fixed nucleotide differences in the ITS and TEF genes that distinguished subgroups separated by RAPD-PCR within species. We confirmed two species of Elsinoë, two pathotypes of E. australis, and at least six pathotypes of E. fawcettii and described their distribution in the countries included in this study.

Improved Method to Increase Conidia Production from Isolates of Different Pathotypes of Citrus Scab Pathogen Elsinoe spp.

“…E. fawcettii can be differentiated into the following six pathotypes: Florida Broad Host Range (FBHR), Florida Narrow Host Range (FNHR), Lemon, Jingeul, SRGC and Tryon's. E. australis has two pathotypes: Sweet orange and Natsudaidai (Hyun et al, 2009). …”

“…A total of 13 isolates belonging to 4 pathotypes of E. fawcettii and E. australis were selected for conidial sporulation assay (Table 1) (Hyun, et al, 2009). All isolates could grow in potato dextrose agar medium.…”

Black Scab of Jojoba (Simmondsia chinensis) in Australia Caused by a Putative New Pathotype of Elsinoë australis

“…In all, 17 isolates of Elsinoë from jojoba were examined for genetic diversity using random amplified polymorphic DNA (RAPD) primers OPX-8, OPX-12, and OPX-17 identified by Hyun et al (12), and compared with 6 Elsinoë isolates from citrus (E. australis strains Ea-2, Ea-4, VRG-BRT, 70212, FZ-STM-CL-1.4, and 70041) (13). Reactions (20 µl) consisted of 1× buffer (Bioline), 0.2 mM each dNTP, 2.5 mM MgCl 2 , 0.5 µM each primer, 1 unit of BioTaq DNA polymerase (Bioline), and 5 ng of template DNA.…”

Molecular Tools for Detection of Plant Pathogenic Fungi and Fungicide Resistance

“…Some of the specific DNA fragments detected in a profile may be cut out of the gel and sequenced to obtain a SCAR (Sequence-characterized amplified region), into which specific primers can be designed for a more precise PCR detection. SCAR primers have been used for instance to specifically identify Phytophthora cactorum (Causin et al, 2005), Fusarium subglutinans (Zaccaro et al, 2007) and Guignardia citricarpa (Stringari et al, 2009) in infected plant material; to distinguish among several formae speciales of Fusarium oxysporum (Lievens et al, 2008); to differentiate the bioherbicidal strain of Sclerotinia minor from like organisms (Pan et al, 2010) (Hyun et al, 2009). This technique has also been applied to differentiate fungi isolates according to their host plant (Midorikawa et al, 2008), enzyme production profiles (Saldanha et al, 2007) or geographical origin and chemotypes (Zheng et al, 2009).…”