Resistance to Three Isolates of Zucchini Yellow Mosaic Virus (ZYMV) in squash (Cucurbita pepo L.)

admin

Cucurbit Genetics Cooperative Report 19:81-82 (article 29) 1996

Ahmed, E.A., A.E. El Jack, A.M. Salama, and G.A. Daffala
Faculty of Agriculture, Abu Haraz, University of Gezira, P.O. Box 42, Wad Medani, Sudan

Zucchini yellow mosaic virus (ZYMV) is a very serious disease in squash, particularly in the central region of the Sudan. A recent survey reported a high incidence and widespread occurrence of the disease in different cucurbit species (3). In many ocasios it causes a total crop loss (1). This project aimed at identifying a source with a suffieiently high level of resistance for incorporating into the popular susceptible cv. Eskandarany (ESK).

Twenty one accessions obtained from the North Central Plant Introduction Station (Ames, Iowa) and 15 breeding lines obtained from Cornell University were evaluated for zucchini yellow mosaic resistance (ZYMR). A scale of 1 to 9 was used, where 1 indicates that a plant is severely infected (showstringing) and 9 indicates no apparent symptoms of the virus. The tissue immuno-blot assay (TIBA) technique was used to detect the virus in the F1 populations (4). The F2 plants were tested at the seedling stage at INRA (Montfavet, France) with the help of Pitrat and Lecoq. Three ZYMV isolates, Su19 and Su4 from central and eastern Sudan, respectively, prepared by Ali (2), and a French isolate, E9, prepared by Lecoq, were used.

None of the PI accessions tested showed an acceptable level of ZYMR. Only two plants in two of the Cornell breeding lines showed a high level (=8) of ZYMR. The first was one out of 7 plants in row 94-38 of the pedigree (91-757 sib PMR + ZYMR pepo). The second was one out of 5 plants in row 94-37 of the pedigree (91-720-2(x), Nigerian Local BC2 cas. F5 , ZYMR.EPS). This level of resistance was retained in the F1 progenies when crossed with the popular susceptible cv, ESK. The TIBA test gave negative results for row 95-13 and 95-14, while row 95-24 results ranged from negative to high in different plants. Approximately 10% of the F2 plants had ZYMR levels similar to that of the donor parents. This indicaes some level of dominance of ZYMR which will permit selecion of resistant plants during successive backcrossing to the cv.ESK. Judging by the overall mean infection rating for three isolates, it appears that plants inoculated with Su19 had the lowest means, 4.4 and 4.3, respectively, while plants infected with Su4 had a slightly higher overall mean of 4.8. This suggests that Su4 is slightly milder than the other two isolates (Table 1). The F2 of 95-14 appears to be the most promising among the F2 ‘s for selection of highly resistant plants with a ZYMR level similar to that of the donor parent.

Table 1. Zucchini yellow mosaic resistance of F2 populations [(ESK x 94-38-1)(x)] to three isolates of ZYMV.

ZYMR rating scale for F2 populations

Isolates

Row No.z

1

2

3

4

5

6

7

8

9

Mean
Number of F2 plants in each rating class
Su 19 95-13 6 10 – 3 4.0
95-14 5 4 7 2 2 4.6
95-24 1 11 2 5 4.6
RCy 2 1 4.6
SCx 2 2 5.3
Su 4 95-13 6 5 5 3 1 4.4
95-14 2 4 5 6 1 5.0
95-24 2 6 3 4 1 5.1
RCy 3 6 5.7
SCx 4 3.0
E 9 95-13 5 11 2 1 3.9
95-14 2 3 8 5 1 5.0
05-24 4 11 1 3.6
RCy 6 6.0
SCx 1 3 3.8

z 95-13 and 95-14 are selfed progenies of two different ESK plants crossed with 94-3801; 95-24 is a selfed progeny of ESK x 94-37-2.
y RC = resistant check, 9505 F1 hybrid tolerant to ZYMV.
x SC = susceptible check, cv. Eskandarany.

Literature cited

  1. Ali, H.M., 1993. Studies on some mosaic-inducing viruses in cucurbits in the Gezira. M.S. Thesis, University of Gezira, Sudan.
  2. Ali, H.M. 1994. Personal communication.
  3. Lecoq, H./, G.A. Daffalla, Y.F. Mohamed, H.M. Ali, C. Wipf-Scheibe, C. Desbiez, A.E. El Jack, S.K. Omara and M. Pitrat. 1994. Survey of virus diseases infecting cucurbit crops in eastern, central and western Sudan. J. Agri. Sci., Univ. Khartoum, V.2, No. 2 (July).
  4. Lin, N.S., Y.H. Hsu and H.T. Hsu. 1990. Immunological detection of plant viruses and mycoplasmalike organisms bydirect tissue blotting on nitrocellulose membrane. Phytopathology 80:824-828.