Dry rot of citrus: pest data sheet

Page last updated: Friday, 9 December 2016 - 2:09pm

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Biology and ecology

Shivas et al. (2005) cite publications that reported E. coryli as a serious disease on multiple citrus varieties in the 1920s and 1930s. During the 1920s in California it was reported to cause desiccation, dry rot and premature fruit drop of orange, grapefruit and tangerine. E. coryli had not been reported as a pathogen of citrus again until 2005, when it was reported in Australia on fruits of Australian lime in Queensland, lemon in Queensland and New South Wales, and mandarin in Queensland (Plant Health Australia 2001, Shivas et al. 2005). Most recently it has also been reported on sweet orange fruit in New South Wales (Plant Health Australia 2001).

Dry rot of citrus results in affected fruits having unpalatable flesh; however, this is not associated with obvious external symptoms at harvest (Cooke et al. 2009). Internally, the predominant symptom is flesh that is dry and brittle. Individual fruit segments have thickened walls and dry flesh, but sometimes this may be restricted to only some segments of an infected fruit (Cooke et al. 2009).

The albedo (inner rind) develops a brown, gummy discolouration and seeds within affected fruit will abort, becoming shrivelled and brownish in appearance (Cooke et al. 2009). Fruit symptoms vary between varieties. For example, in lemon there is often severe albedo browning and seed abortion, whereas red-fleshed grapefruit may remain asymptomatic (Cooke et al. 2009). Mandarin and lemon in Australia are often associated with dry flesh symptoms (Cooke et al. 2009).

Little information is available about the aetiology or epidemiology of dry rot of citrus in Australia (Shivas et al. 2005). E. coryli produces few hyphae and can reproduce vegetatively via budding and ascospores (Mukerji 1964), but these structures have not been reported as essential for pathogen dispersal in citrus or alternative hosts. In addition to citrus, this fungus is known to be a widespread pathogen of seeds of multiple tropical and subtropical plants (Mukerji 1964). However, spread of E. coryli by citrus seeds has not been reported. 

Dispersal of E. coryli is predominantly due to mechanical transmission by feeding of pentatomid (Hemiptera) insects. Citrus fruits must be punctured during feeding for infection to occur (Mukerji 1964). E. coryli is known to persist in vectors (Mukerji 1964, Kulik and Sinclair 1993, Shivas et al. 2005) and the presence of vectors, even in low numbers, can result in significant levels of fruit damage (Cooke et al. 2009).

In Australia, there are two known vectors of E. coryli on citrus, spined citrus bug (Biprorulus bibax) and green vegetable bug (Nezara viridula) (Smith et al. 1997, Shivas et al. 2005, Cooke et al. 2009). The spined citrus bug is exotic to Western Australia but the green vegetable bug is already established. There are no other known hemipteran pests of citrus in Western Australia. However, that does not preclude other native insects from playing a role in the dispersal of E. coryli. Further research is needed to determine alternative vectors that may occur for E. coryli in Australia (Shivas et al. 2005).

Shivas et al. (2005) query whether endemic Australian species of Hemiptera feeding on grain legumes, cotton and macadamia in the eastern states are possible vectors of E. coryli since these hosts are known to be infected by E. coryli in other countries (Mukerji 1964). Pentatomids of the genera Antestiopsis and Dysdercus nigrofasciatus are also thought to vector E. coryli in some hosts (Mukerji 1964). Antestiopsis species have not been reported to feed on citrus species in Australia, and D. nigrofasciatus is exotic to Australia. However, other species of these genera are known to occur in Western Australia (Plant Health Australia 2001).

E. coryli has been reported on numerous tropical and subtropical hosts in other countries. However, Shivas et al. (2005) suggest that the presence of E. coryli on Australian lime may indicate that this pathogen is endemic to Australia, and has moved from Australian lime to infect cultivated citrus. The presence of infected alternative hosts near citrus orchards are believed to provide an inoculum source (Shivas et al. 2005, Cooke et al. 2009). There are no endemic native citrus species in Western Australia; however, there are minor crops of finger lime and also backyard trees (Citrus australasica and other native citrus hybrids). Other known alternative hosts are distributed widely throughout Western Australia either as commercial crops or in home gardens.

Shivas et al. (2005) suggest that further research is required in Australia to determine whether E. coryli occurs on alternative hosts (that is, as reported in other countries), its possible presence on native and weedy plants, and to determine a list of insect vectors.

Economic consequences

E. coryli is also known to be a serious pathogen of seeds of many tropical and subtropical plant species, including many cultivated in Western Australia such as citrus, soybean, cotton, tomato and Macadamia species (Shivas et al. 2005).

E. coryli is likely to have been the cause of citrus fruit and seed defects in eastern Australia that were previously attributed to other causes such as bacterial infection, insect damage and boron deficiency (Shivas et al. 2005). The role insect vectors play in the transmission of E. coryli within citrus has only recently been reported, despite disease symptoms affecting cultivated mandarins and lemons in Australia since the early 1900s (Shivas et al. 2005, Cooke et al. 2009). Where insect vectors are not controlled, entire crops of lemons, mandarins and citrus rootstock seed can be affected (Cooke et al. 2009).

Where fruit infections occur but remain undetected during packing, the subsequent sale of unpalatable fruit may result in poor consumer confidence (Cooke et al. 2009).

What do I do if I find it?

Eremothecium coryli (Peglion) Kurtzman 1995 is a prohibited organism for Western Australia. It is important that suspect disease occurrence is reported. Early detection and eradication will help protect Western Australian citrus growers. Please contact the Pest and Disease Information Service to report this pest.


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Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080