Citrus leaf spot diseases caused by Cryptosporiopsis citricarpa and C. citri
Two citrus leaf spot diseases caused by new fungus species, Cryptosporiopsis citricarpa and C. citri have been observed in China and Oceania, respectively. Cryptosporiopsis species are the anamorphs of Pezicula or Neofabraea, but the teleomorphs of both C. citricarpa and C. citri are unknown. These two citrus diseases can cause defoliation and tree dieback, but do not affect citrus fruit directly.
- Cryptosporiopsis citricarpa sp. nov.
In winter 2006, an unusual leaf spot disease of Satsuma mandarins (Citrus unshiu) and kumquats (Fortunella margarita) was noticed in Chenggu county (Shaanxi province) in China. The causal agent was described as a new fungus species: Cryptosporiopsis citricarpa sp. nov (Zhu et al., 2012). This new citrus disease, called ‘target spot’, usually appeared around mid-December and peaked in February. Infected leaves show small, needle-like, reddish-brown lesions which enlarge to become circular to oval spots (1-13 mm in diameter). On the lower leaf surface, lesions are often surrounded by an oily halo. Leaf spots then become a paler shade (starting from the centre) and black dots (acervuli) are produced in a circular arrangement on the upper surface of the lesions (hence the name ‘target spot’). Lesions can also be observed on petioles, shoots, branches or trunks, but citrus fruit are not affected. This disease can lead to severe defoliation, dieback and eventually tree mortality. In the Chenggu county, the disease has gradually become more important affecting a large proportion of citrus trees and causing tree mortality. It is noted that C. citricarpa is causing substantial economic losses in citrus production in Chenggu county (without further details). Surveys have been conducted during the last three years in China, and did not detect C. citricarpa in any other citrus-growing regions.
- Cryptosporiopsis citri
In 1998, a new fungus species, Cryptosporiopsis citri, was described from citrus trees affected by a leaf spot disease (Johnston ; Fullerton, 1998). C. citri was found on Citrus aurantifolia, C. limon, C. sinensis in several Pacific Islands (Cook Islands, Fiji, Niue, Samoa, Tonga, and Vanuatu). Affected citrus trees showed circular leaf spots (3-5 mm in diameter), slightly depressed, pale grey to brown with a dark-brown border. In some areas, trees were severely affected with many of the diseased leaves falling prematurely. C. citri has not been found associated with citrus fruit. The authors considered that although the symptomatology is different, the causal agent of this new leaf spot disease has been misidentified during past surveys in the above Pacific Islands as Phyllosticta citricarpa (anamorph of Guignardia citricarpa – EPPO A1 List). In November 2007, C. citri was detected on C. aurantifolia on a property in Virginia, Northern Territory, Australia. Delimiting surveys were carried out in Northern Territory and showed that C. citri was only present in this property where eradication measures have been taken.
Sources
Johnston PR, Fullerton RA (1998) Cryptosporiopsis citri sp. nov.; cause of a citrus leaf spot in the Pacific Islands. New Zealand Journal of Experimental Agriculture 16(2), 159-163.
Ray JD, McTaggart AR, Shivas RG (2008) First record of Cryptosporiopsis citri on lime in Australia. Australasian Plant Disease Notes 3(1), 158-159.
Zhu L, Wang X, Huang X, Zhang J, Li H, Ding D, Hyde KD (2012) A destructive new disease of Citrus in China caused by Cryptosporiopsis citricarpa sp. nov. Plant Disease 96(6), 804-812.