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Poplar plantations provide important industrial feedstock in China. Red spot symptoms were observed on leaves of Populus tomentosa and P. deltoides in southeastern China. Based on morphology and molecular phylogenetic analysis, the fungus isolated from disease spots was identified as Elsinoë australis, which has been previously recognized as a pathogen of Citrus spp. and jojoba but has not been reported in China. Pathogenicity tests found that isolates from two poplar species caused red spot symptoms on leaves from different poplar species and also led to scab formation on the fruit of one hybrid citrus but not on fruit of orange, lemon, or grapefruit. The draft genome of one E. australis isolate was generated. The genetic architecture of the MAT1-1 and MAT1-2 loci of E. australis was revealed by genome sequence and long-range PCR analyses. Single isolates carried only one of two opposite mating-types was confirmed by idiomorph-specific PCR, suggesting a heterothallic mating system. Our results not only revealed a new E. australis pathotype causing poplar spot anthracnose in China but also provided its genome and mating system information.

A new disease of jojoba in Australia is described. We have demonstrated that this disease is caused by Elsinoë australis, a pathogen which is normally associated with citrus. This pathogen has not been found previously in Australia on citrus or any other crop. The fungus causes a scab on leaves and stems of jojoba and is widely distributed in eastern Australia. Although molecular analysis of the pathogen indicates that it is closely related to the natsudaidai and the sweet orange pathotypes of E. australis, glasshouse and laboratory experiments demonstrate that it is not pathogenic to a range of citrus cultivars grown in Australia. The data indicate that the isolates from jojoba represent a new pathotype of E. australis.

Sweet orange scab (SOS) is a fungal disease of citrus which is caused by Elsinoe australis. It affects the aesthetics of the fruit by forming wart-like protruded lesions on the fruit skin, and also affects the leaves which act as source of inoculum in the orchards. SOS is widespread in the different citrus species such as grapefruit (Citrus x paradisi Macfd.), sweet orange [C. sinensis (L.) Osb.], and mandarin (C. reticulata Blanco). In this study, we report the development of symptoms and changes in polyphenolic profile of ‘Rio Red’ grapefruit leaves in response to E. australis infection. Qualitative and quantitative analysis of polyphenols in ‘Rio Red’ grapefruit leaves inoculated with E. australis were conducted using high performance liquid chromatography (HPLC) at two different time points post inoculation. Development of SOS symptoms under light was recorded and categorized into four different morphological stages. Caffeic acid, luteolin-7-O glycoside, naringin, naringenin, apigenin-7-O glycoside and eriodictoyl were identified in healthy grapefruit leaves. The quantitative changes in the identified polyphenols were measured 9 days post-inoculation by comparing levels on the 9-day control versus the 9-day post-inoculated leaves. Total polyphenol levels decreased substantially in E. australis-infected ‘Rio Red’ grapefruit leaves 9 days post-inoculation. Levels of naringin, naringenin, apigenin glucoside and eriodictoyl decreased with E. australis infections indicating the pathogen’s ability to overcome some of plant’s defenses. Compared to 9-day controls, 9-day inoculated leaves had much less caffeic acid.

Elsinoe fawcettii and E. australis are two currently recognized scab pathogens of citrus. E. fawcettii has at least six pathotypes while E. australis has at least two pathotypes. Colonies of E. fawcettii and E. australis do not sporulate in artificial media including potato dextrose agar (PDA). Whiteside's method has been widely used for preparing conidial inoculum in vitro. This study was carried out to develop efficient method for conidia production from artificial media. We developed a shaking method which included the following steps: 1) Colony grown on PDA was mashed with a steel spatula; 2) Mycelia fragments were cultured in 50 ml sterilized rain water in a rotary shaker-incubator (180 rpm) at 25°C for 24 h: 3) The conidia suspension was filtered through two layers of cheesecloth. Average conidia production of all isolates tested using this shaking method was approximately 13.1 times higher than that from Whiteside’s method in this study.

Elsinoe fawcettii and E. australis are important pathogens of citrus. Both species are known to produce red or orange pigments, called elsinochrome. Elsinochrome is a nonhost-selective phytotoxin and is required for full fungal virulence and lesion formation. This article discusses the taxonomy, epidemiology, genetics and pathology of the pathogens. It also provides a perspective on the cellular toxicity, biosynthetic regulation and pathological role of elsinochrome phytotoxin. Taxonomy: Elsinoe fawcettii (anamorph: Sphaceloma fawcettii) and E. australis (anamorph: S. australis) are classified in the Phylum Ascomycota, Class Dothideomycetes, Order Myriangiales and Family Elsinoaceae. Host range: Elsinoe fawcettii causes citrus scab (formerly sour orange scab and common scab) on various species and hybrids in the Rutaceae family worldwide, whereas E. australis causes sweet orange scab, primarily on sweet orange and some mandarins, and has a limited geographical distribution. Disease symptoms: Citrus tissues infested with Elsinoe often display erumpent scab pustules with a warty appearance. Toxin production: Elsinochrome and many perylenequinone-containing phytotoxins of fungal origin are grouped as photosensitizing compounds that are able to absorb light energy, react with oxygen molecules and produce reactive oxygen species, such as superoxide and singlet oxygen. Elsinochrome has been documented to cause peroxidation of cell membranes and to induce rapid electrolyte leakage from citrus tissues. Elsinochrome biosynthesis and conidiation are coordinately regulated in E. fawcettii, and the environmental and physiological inducers commonly involved in both processes have begun to be elucidated.

Genetic differences among three citrus scab pathogens were investigated. The three pathogens were (i) the cosmopolitan Elsinoe fawcettii causing citrus scab, (ii) E. australis from South America causing sweet orange scab, and (iii) Sphaceloma fawcettii var. scabiosa from Australia causing Tryon's scab. In a companion study, we were unable to differentiate these taxa morphologically, but were able to differentiate E. fawcettii, E. australis, and S. fawcettii var. scabiosa pathologically. Two pathotypes of E. fawcettii from Florida and two pathotypes from Australia were distinguished on the basis of host range. Restriction analysis of the amplified internal transcribed spacer (ITS) of ribosomal DNA with several endonucleases and sequence analysis of the ITS readily differentiated E. australis from E. fawcettii and S. fawcettii var. scabiosa. Random amplified polymorphic DNA (RAPD) analysis indicated that E. fawcettii isolates from Australia and from Florida were more closely related to each other than to E. australis isolates from Argentina. However, all Australian isolates were separable from all Florida isolates by their RAPD profiles. There was a good correspondence between the RAPD profiles and the two pathotypes identified in Australia. Molecular analysis will be a rapid, useful tool in identifying exotic types of citrus scab on shipments of fruit and help reduce introductions of these types into new areas.

Three scab diseases have been described on citrus: (i) citrus scab caused by Elsinoe fawcettii, which is cosmopolitan in humid citrusgrowing areas; (ii) Tryon's scab caused by Sphaceloma fawcettii var. scabiosa, which occurs in Australia and elsewhere; and (iii) sweet orange scab caused by E. australis, which occurs primarily in southern South America. In this study, we compared isolates from Australia, Argentina, and Florida (United States). Neither colony color nor conidial size or shape could be used to distinguish the three scab fungi on citrus. A detached-leaf assay was developed to compare pathogenicity of isolates on rough lemon, sour orange, and grapefruit. All isolates from Australia produced scab only on rough lemon, whereas all isolates from Florida produced scab on rough lemon and grapefruit and a portion of these also produced scab on sour orange. E. australis isolates from Argentina did not affect leaves of any species. One E. fawcettii isolate from Argentina produced the same reaction as Australian isolates, and two produced the same reaction as the Florida group that affected rough lemon, grapefruit, and sour orange. In greenhouse inoculations, all Australian isolates infected rough lemon, lemon, and Rangpur lime; all but a few also infected Cleopatra mandarin. In greenhouse inoculations in Florida, all isolates infected rough lemon and Cleopatra mandarin and some isolates infected sour orange. Although E. australis is not readily differentiated from E. fawcettii morphologically, we concluded that they are separate species on the basis of pathogenicity and molecular analysis. S. fawcettii var. scabiosa could be differentiated from E. fawcettii only by host range. We recognized four pathotypes of E. fawcettii: the Broad Host Range and Narrow Host Range pathotypes originally described in Florida, the Tryon's pathotype (formerly S. fawcettii var. scabiosa), and a new Lemon pathotype from northern Australia.