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Cucurbit Genetics Cooperative Report 12:1-4 (article 1) 1989

Alternaria alternata f. sp. cucurbitae on Cucumber and Other Cucurbits

Demetrios John Vakalounakis

Plant Protection Institute, Heraklio, Crete, Greece

During the 1979 to 1980 crop season, a severe leaf spot disease of cucumber (Cucumis sativus L.) was noticed on greenhouse crops grown in some plastic houses in the Sitia Area, Lasithi, Crete, Greece, along the coastal strip between Koutsouras and Goudouras (10). Since then, it has spread to most of the cucumber growing areas in Crete, causing severe losses.

Symptoms appear in late autumn, mainly on the leaves of the middle and upper part of the plants. Necrotic flecks, surrounded by a chlorotic halo, appear on the leaf, and these enlarge to spots which may coalesce to form lesions up to 5 cm or more in diameter. The lesions appear circular in shape and bear black-brown fructifications of the pathogen. Severely-infected leaves become yellow, senescent, and die. No other part of the plant is affected. During the winter, when relative humidity in the plastic houses is high and plant vigor is reduced due to fruit bearing and unfavorable climatic conditions (reduced illumination and average air temperature lower than 15°C), infection progresses rapidly throughout the crop resulting in severe damage within a few days (11).

A long-chained Alternaria spp. with small spores was always observed on the old lesions of infected cucumber leaves. The same fungus was consistently obtained from samples taken from different plastic houses when pieces of infected tissue or spores from the spots were plated out on Petri dishes containing potato dextrose agar (PDA). The cultures of the fungus on PDA at 25°C under "daylight" fluorescent lamps have a dirty white color at the beginning, while later the center becomes gray. In a few days, the entire surface is covered with an abundance of spores. The spores on infected leaves or on cultures on PDA are produced in long chains on short conidiophores. They are brown but, when many of them have been produced on PDA, they look black with a velvety appearance. The dimensions of the spores either in vivo or in vitro (Table 1) agree fairly well with published descriptions of Alternaria alternata (Fr.) Keissler (8) and its synonym Alternaria tenuis Auct. (6, 7). The pathogen of the present disease is also similar to A. alternata f. sp. lycopersici which causes a stem canker of tomato (2). Alternaria infections similar to those described in this paper are very common on cucumber but are caused by Alternaria cucumerina (Ellis & Everh.) Elliott (synonym Alternaria brassicae f. nigrescens Pegl.) (1, 5) or Alternaria pluriseptata (Karst. & Har.) Jorstad [synonyms Alternaria cucurbitae Let. & Roum., Stemphylium ilicis Tengwall, Ulocladium cucurbitae (Let. & Roum.) Simmons, Ulocladuim atrum Press] (3, 9). However, both these fungi are morphologically distinct (1, 4, 5, 6) and are readily distinguishable from Alternaria alternata (11).

Of 62 cultivated and weedy species in 16 botanical families artificially inoculated and naturally infected in greenhouse experiments, 27 species belonging to the Cucurbitaceae were found to be susceptible to the pathogen (Table 2).

Table 1. Morphological characteristics of conidia of Alternaria alternata f. sp. cucurbitae from cucumber leaf spots in comparison with those of published descriptions of A. alternata, A. cucumerina and A. pluriseptata.

Spore measurements (µm)

Body length

Body width

Beak length

Spores (% with beaks)

Total length

No. of septa

Spores/chain

A. alternata

Cucumber leaf spot

3804±12.0z (15-68) y

14.6±3.3 (9-24)

6.3±4.4 (1-21)

75

42.2±14.3 (15-73)

2-8

4-5

PDA

20.1±4.8 (12-29)

9.7±2.0 (6-14)

5.1±2.3 (3-12)

57

25.3±4.5 (17-34)

2-5

8

A. alternata (Simmons, 1967)

Neotype specimen

30.9 (18-47)

12.6 (7-18)

up to 25

-

-

3-8

-

A. tenuis

Medium

25.7 (7-70)

11.2 (6-20)

5 (1-58)

80

7-72

1-6

8

A. alternata f. sp. lycopersici

Tomato

32.3±2.8 (18-50)

12.4±2.8 (7-18)

6.8±6.0 (2-20)

72

18-68

1-5

3-4

A. cucumerina (Jackson, 1958)

Host

57-87

18-21

106-135

-

-

5-9

-

A. pluriseptata (Hervert et al., 1980)

Host

19-66

8-16

-

-

-

2-9

-

Ulocladium atrum (Simmons, 1976)

Medium

18.6

16.5-19.8

16.0

13.2-18.7

no beaks

-

-

1-3

1; sometimes 2

z Mean ± standard deviation.
y Numbers in parentheses indicate extreme values.

Table 2. Susceptibility of cucurbitaceous species and some belonging to other families to infection by Alternaria alternata f. sp. cucurbitae.

Species

Disease severity

CUCURBITACEAE

Benincasa hispida ( Thumb.) Cogn.

+++

Citrullus lanatus ( Thumb.) Mansf.

++++

Cucumis africanus L. f.

+

Cucumis anguria L.

+++

Cucumis dipsaceus Ehrenb.

+

Cucumis ficifolius A. Rich

++

Cucumis hardwickii Royle

++++

Cucumis longipes Hook.

++

Cucumis melo L.

++++

Cucumis pustulatus

++++

Cucumis sativus L.

+++++

Cucurbita ficifolia B.

+

Cucurbita foetidissima Kunth.

+

Cucurbita lundelliana Bailey

++

Cucurbita maxima Duch.

+

Cucurbita mixta Pang.

+++

Cucurbita moschata (duch.) Duch. ex Poir.

+++

Cucurbita palmeta Wats.

+++

Cucurbita pepo L.

+++

Cucurbita sororia

+++

Cucurbita texana A. Gray

+

Ecballium elaterium (L.) A. Rich

+

Lagenarial leucantha Rusby var. clavata Makino

+++++

Lagenaria siceraria (Mol.) Standl. ssp. asiatica (Kob). Heiser

++++

Lagenaria vulgaris Ser.

+++++

Luffa cylindrica Roem.

++

Momordica charantia L.

+++

SOLANACEAE

Capsicum annuum L.

-

Lycopersicon esculentum Mill.

-

Nicotiana tabacum L.

-

Nicotiana glutinosa L.

-

Solanum melongena L.

-

UMBELIFERAE

Apium graveolens L.

-

Daucus carota L.

-

URTICACEAE

Urtica urens L.

-

AMARANTHACEAE

Amaranthus retroflexus L.

-

Gomphrena globosa L.

-

CHENOPODIACEAE

Beta Vulgaris L.

-

Chenopodium album L.

-

Spinacia oleracea L.

-

COMPOSITAE

Aster squamatus ( Spr.) Hier.

-

Cichorium endivia L.

-

Chichorium intybus L.

-

Erigeron canadensis L.

-

Lactuca sativa L.

-

Lactuca serriola L.

-

Sonchus asper (L.) Hill.

-

CONVOLVULACEAE

Convolvulus arvensis L.

-

CRUCIFERAE

Brassica oleracea L. var. capitata

-

Raphanus sativus L.

-

CYPERACEAE

Cyperus longus L.

-

var. badius Desf.

-

GERANIACEAE

Erodium malacoides Willd.

-

GRAMINAE

Setaria viridis P.B.

-

LEGUMINOSAE

Glycyrriza glabra L.

-

Medicago polymorpha L.

-

Melilotus indica All.

-

Phaseolus vulgaris L.

-

Vicia faba L.

-

LILIACEAE

Allium cepa L.

-

OXALIDACEAE

Oxalis corniculata L.

-

ROSACEAE

Fragaria vesca L.

-

- no disease; + to +++++ increasing amount of disease.

Literature Cited

  1. Ellis, M.B., and P. Holliday. 1970. Alternaria cucumerina. C.M.I. Descriptions of pathogenic Fungi and Bacteria. No. 244.
  2. Grogan, R.G., K.A. Kimble, and I. Misaghi. 1975. A stem canker disease of tomato caused by Alternaria alternata f. sp. lycoperisici. Phytopathology 65: 880-886.
  3. Hervert, V., L. Marvanova, and V. Kazda. 1980. Alternaria pluriseptata on cucumbers and remarks to its classification. Ceska Mycologie 34: 13-20.
  4. Jackson, K.R. 1958. Taxonomy and host range of Alternaria cucumerina. Phytopathology 48: 343-344.
  5. Jackson, C.R., and G.F. Weber. 1959. Morphology and taxonomy of alternaria cucumerina. Mycologia 51: 401-408.
  6. Groves, J.W., and A.J Skolko. 1944. Notes on seedborne fungi. II. Alternaria. Can. J. Res. 22:217-234.
  7. Neergaard, P. 1945. Danish species of Alternaria and Stemphylium. Oxford University Press, London. 560 pp.
  8. Simmons, E.G. 1967. Typification of Alternaria, Stemphylium, and Ulocladium. Mycologia 59: 67-92.
  9. Simmons, E.G. 1982. Alternaria themes and variations (11-13). Mycotaxon 14: 44-57.
  10. Vakalounakis, D.J. and N.E. Malathrakis. 1982. A cucumber disease caused by the fungus Alternaria alternata. 2nd Conf. Protected Veg. Flowers, Heraklion, Crete, Greece.
  11. Vakalounakis, D.J. and N.E. Malathrakis. 1988. A cucumber disease caused by Alternaria alternata and its control. Z. Phytopathology 121: 325-336.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 23 October, 2009