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Plantwise Technical Factsheet

stalk end rot (Alternaria citri)

Host plants / species affected
Argyreia nervosa (elephant creeper)
Citrus
Citrus jambhiri (rough lemon)
Citrus junos (yuzu)
Citrus limon (lemon)
Citrus medica (citron)
Citrus reticulata (mandarin)
Citrus sinensis (navel orange)
Gerbera (Barbeton daisy)
Withania somnifera (poisonous gooseberry)
List of symptoms/signs
Fruit  -  discoloration
Fruit  -  lesions: black or brown
Fruit  -  premature drop
Leaves  -  abnormal colours
Leaves  -  abnormal leaf fall
Leaves  -  necrotic areas
Symptoms
A. citri is responsible for various diseases in fruits and leaves of species of Citrus, namely, black rot of oranges, fruit rot of lemons and tangerines, stem end rot of lemons and leaf spot of rough lemon and Emperor mandarin (Ellis and Holliday, 1970; Ellis, 1971).

Black rot of oranges begins at the blossom end of the fruit and causes premature ripening and dropping of the fruits. There is no external sign of the rotting, but internal decay begins near the stylar end of the fruit. In advanced stages, the internal rotting area expands and turns dark green or black. The condition may be aggravated by weather and the nutrient balance of the host.

On lemons, a soft, central rot occurs in mature fruit, beginning at the button and spreading to the axis. Before the rot appears on the fruit surface, the rind becomes translucent. There is also an end rot in which the external spread is almost as extensive as that inside the fruit.

In some cases, rotting of lemons also starts at the stem end and the peel is the last part to be affected.

In rough lemons, circular or irregular, necrotic spots with concentric zonings are produced on the leaves, followed by a general chlorosis, curling and leaf drop.
Prevention and control
The timely picking of mature or even unripe fruits is the best approach to preventing black rot of oranges in the field. However, if black rot has developed, picking may be delayed to allow any infected fruit to drop.

Intermittent warming treatments at 13°C reduced decay in lemons stored at 2-8°C; greatest reductions in decay caused by A. citri were obtained with two cycles of 2 weeks at 2°C and 2 weeks at 13°C with 79.5% RH (Artes et al., 1993). Low hormetic doses of ultraviolet light (254 nm) also reduced postharvest decay of citrus fruits caused by A. citri (Stevens et al., 1996).

Preharvest application of thiophanate-methyl and sorting of healthy fruits were directly related to the maintenance of fruit quality during Satsuma mandarin storage (Nam et al., 1993).

Treatment with thiabendazole (Javed et al., 1995) and volatile compounds produced by Trichoderma hamatum (Dal-Bello et al., 1997) have been shown to inhibit the growth of A. citri.

Cupric hydroxide gave the best control of A. citri on tangelo, reducing the number of lesions on infected fruit by 75 and 57% for the high (10 or 11) and low (five or six) spray frequencies, respectively, compared with untreated fruits (Olson et al., 1992).

Iprodione controlled A. citri infection in Israel when sprayed four or five times at 14-day intervals, beginning shortly after full bloom in April (Sole et al., 1997). Other effective fungicides were metiram, folpet, Bordeaux mixture and copper oxychloride (Kumar and Grover, 1964; Chand et al., 1967; Pathak, 1980; Sole et al., 1997). Iminoctadine was partially effective against black rot of oranges (Koizumi, 1992).

After the failure to control the navel end rot on navel oranges with contact fungicides in South Africa, new systemic triazole fungicides (difenoconazole and tebuconazole) were tested and found to be effective for this purpose (Schutte et al., 1994).

Postharvest biological control of citrus fruit rot has been suggested by treatment with Bacillus sphericus and Candida sp. (Sharma, 1993) and sprays of Trichoderma viride, T. harzianum, Gliocladium roseum and Paecilomyces variotii (Pratella and Mari, 1993).

The use of resistant mandarin varieties against A. citri has also been proposed in New Zealand (Harty et al., 1992).
Impact
Surveys in several districts of Maharashtra state, India, during 1988-90 indicated that 43 and 47% of the total losses of mandarins in truck and train transport, respectively, were due to postharvest diseases; more than 20% of the losses were caused mainly by A. citri (Naqvi and Dass, 1994).
Related treatment support
 
External factsheets
University of California IPM Pest Management Guidelines, University of California, 2008, English language
USDA-APHIS-PPQ CPHST Citrus Diseases Fact Sheets, USDA-APHIS-PPQ Center for Plant Health Science and Technology (CPHST), 2011, English language
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