Cucurbit Genetics Cooperative Report 4:30-32 (article 15) 1981

A New Watermelon Disease In Tunisia

Hager Jebari

Laboratory for Vegetable Crops, I.N.R.A.T., Tunisia

A very serious, new bacterial disease, not yet identified, has been reported on watermelon in 1978, on both early planting (January) and later plantings (March) in the Sahel and the Cap Bon in Tunisia.

The disease appears as large, black spots on the leaves at the middle of the plant, near the principal stem followed by a withering of the entire plant. As a result, the fruits ripen prematurely. In 1979, an early planting of several cultivars of watermelon revealed a very small difference in sensitivity among these cultivars (Table 1). Only Citrullus colocynthis, which is a wild species, has shown a very good behavior and complete resistance to this disease in the field. In 1980, the results from two watermelon planting confirmed the previous observations (Table 1).

Based on these results, C. colocynthis has been selected as a source of resistance to this disease. The F₁ hybrid between the common watermelon C. lanatus and C. colocynthis and BC₁ has been made, which will be used in studying the inheritance of resistance to this disease. The ultimate objective is to obtain a C. lanatus type with resistance to this new bacterial disease and free from the bitterness of C. colocynthis (1-4).

Table 1. Reaction of watermelon cultivars and Citrullus colocynthis to a new bacterial disease.

	1979 z			1980
Cultivars	6 June	15 June	28 June	15 June y	15 August x
Algerian Red Seed	-	-	-	5 w	-
Ali	3	4	4	5	-
Arizona	-	-	-	-	4
Betima	-	-	-	3.5	-
Blue Belle	2.5	4.5	4	-	5
Blue Ribbon	-	-	-	-	4
Charleston Gray	-	-	-	-	5
Chilean Black	-	-	-	-	5
Congo	-	-	-	5	5
Crimson Sweet	3.5	4	4	5	-
Early Canada	1.5	3.5	4	-	-
Fairfax	-	-	-	-	5
Garrisonian	-	-	-	-	5
Giza	1	2.5	4	-	4
Giza 1	-	-	-	3.5	-
Giza 2	-	-	-	4	-
Hramorni	2.5	3.5	4	3	-
Klondike RS 57	-	-	-	-	3.5
Klondike X	-	-	-	-	4
Klondike VII	-	-	-	-	5
Marzowsky	-	-	-	-	4
Panonia	-	-	-	5	5
Peacock Striped	2	3.5	4	4	-
Pobeditel	4	4	4	5	-
Red New Dragon	3	5	4	-	-
Royal Charleston	-	-	-	-	5
Royal Flesh	1.5	3.5	4	-	-
Ruby T.S.	2	4.5	4	-	-
Sugar Baby	-	-	-	5	-
Sugar Bell 126	1	5	4	-	-
Sugar Delikata	1.5	4.5	4	-	-
Sugar Sweet	-	-	-	-	5
Sweet Favorita	-	-	-	-	4
Tasty	-	-	-	5	5
Tatum	2	3.5	4	-	-
Wide Ranger 118	4	4	4	-	-
XP 241	2	3.5	5	-	-
XP 772	2	3	3	-	-
XP 1023	2	3.5	4	-	-
XP 1203	-	-	-	-	4
XP 2008	1	4	4	-	4
You Sweet Thing	-	-	-	-	5
117	4	4.5	5	-	-
3527	1	2.5	4	-	-
3807	1	3	4	-	5
7486 M	1	2.5	4	-	-
37486 N	3	2.5	4	-	-
Citrullus colocynthis (1)	-	-	-	1	1
Citrullus colocynthis (2)	-	-	-	0.5	0.5

^z Planted on 13/2/79.
^y Planted on 17/1/80.
^x Planted on 15/3/80.
^w 5 = Susceptible, 0 = Resistant.

Literature Cited

1. Enslin, P. R. and S. Rehn. 1957. The distribution and biogenesis of the cucurbitacins in relation of the Cucurbitaceae. Proc. Linn. Soc. (London) 169: 230-238.
2. Furosato, K. and A. Miyazawa. 1957. Crossing experiments with Citrullus vulgaris Schrad. and Citrullus colocynthis Schrad. Natl. Inst. Genetics Ann. Rpt. (Japan) 7: 45-47.
3. Shimotsuma, M. 1963. Cytogenetical studies in the genus Citrullus. VII. Inheritance of several characters in watermelons. Jap. J. Breeding 13: 235-240.
4. Shimotsuma, M. and Y. O. Gawa. 1960. Cytogenetical studies in the genus Citrullus. Bitter substances in fruits of C. colocynthis Schrad. and C. vulgaris Schrad. Jap. J. Genetics 35: 143-152.