Cucurbit Genetics Cooperative Report 7:43-44 (article 19) 1984

Interaction of Zucchini Yellow Mosaic Virus Strains and Muskmelon Lines

Lecoq, H. and M. Pitrat

I.N.R.A., Centre de Recherches Agronomiques d'Avignon, B.P. 94, 84140 Montfavet, France

Zucchini yellow mosaic virus (ZYMV), a recently described member of the potyvirus group (3), is now commonly found infecting cucurbits in various parts of the world (2). It induces severe symptoms including mosaic, leaf deformations, plant stunting, necrosis and fruit alterations.

In muskmelon, two pathotypes were distinguished on 'Doublon' (1). One is pathotype F which causes a rapid wilting of the plant and subsequent general necrosis (WN). The second is pathotype NF which causes vein clearing, yellowing, mosaic and leaf deformations (VcY). Both pathotypes induce VcY symptoms in 'Vedrantais' muskmelon. The WN reaction of 'Doublon' has been attributed to the action of the semidominant Flaccida necrosis gene, symbolized (Fn) (5).

Muskmelon plant introduction (PI) 414723 is partially resistant to ZYMV (4). Most plants of PI 414723 remain symptomless when inoculated with strain E15 (pathotype NF) or with strain 1318 (pathotype F) and the virus does not become systemic. This resistance is controlled by the dominant gene Zucchini Yellow Mosaic, symbolized (Zym) (4). Some plants may, however, develop systemic, chloronecrotic lesions from which the virus may be recovered.

Some ZYMV strains, such as the ZYMV type strain from Italy (3) (pathotype NF) and strain E9 (pathotype F), induce systemic, chloronecrotic lesions on all inoculated PI 414723 plants. The virus can be recovered from the apex of plants infected with these strains. From such plants, we have selected in the laboratory ZYMV strains that completely overcome the resistance of PI 414723 and induce on this line typical VcY symptoms.

These results suggest another classification of ZYMV strains based on the symptoms of PI 414723 and 'Doublon' (Table 1).

Table 1. Classification of 6 ZYMV strains according to the reaction of PI 414723 and 'Doublon' muskmelon lines.
PI 414723	Doublon
	Vein clearing yellowing (Pathotype NF)	Wilt necrosis (Pathotype F)
Symptomless (Pathotype 0)	E15	1318
Systemic, chloronecrotic lesions (Pathotype 1)	ZYMV type, Italy	E9
Vein clearing yellowing (Pathotype 2)	D41	Bo 21

It appears that the ability of a ZYMV isolate to induce the wilting reaction in 'Doublon' is independent of its virulence in PI 414723. The observed variability in the pathogenicity of ZYMV is important, and emphasizes the need for other sources of resistance to ZYMV even though pathotype 2 has not yet been found in the field.

Literature Cited

1. Lecoq, H., M. Pitrat and M. Clément. 1981. Identification et caractérisation d'un potyvirus provoquant la maladie du rabougrissement Jaune du Melon. Agronomie 1:827-834.
2. Lecoq, H., V. Lisa and G. Dellavalle. 1983. Serological identity of Muskmelon Yellow Stunt and Zucchini Yellow Mosaic Viruses. Plant Disease Reptr. 67:824-825.
3. Lisa, V., G. Boccardo, G. d'Agostino, G. Dellavalle and M. d'Aquilio. 1981. Characterization of a potyvirus that causes Zucchini-Yellow mosaic. Phytopathology 71:668-672.
4. Pitrat, M. and H. Lecoq. 1984. Inheritance of Zucchini Yellow Mosaic Virus resistance in Cucumis melo L. Euphytica 33 (in press).
5. Risser, G., M. Pitrat, H. Lecoq and J. C. Rode. 1981. Sensibilité variétale du melon (Cucumis melo L.) au Virus du Rabougrissement jaune du melon et à sa transmission par Aphis gossypii Glov. Hérédite dé la réaction du flétrissement. Agronomie 1:835-838.