Selection of Squash (Cucurbita pepo L.) Lines Resistant to Zucchini Yellow Mosaic Virus (ZYMV) in Sudan

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Cucurbit Genetics Cooperative Report 22:55-56 (article 20) 1999

H.S. Ibn Oaf, E.A. Ahmed, A.E. El Jack and G.A. Daffalla
Faculty of Agricultural Sciences, University of Gezira, P.O. Box 20, Wad Madani, Sudan

Zucchini yellow mosaic virus causes a very serious disease of squash in Sudan, particularly in the central region. On many occasions it causes a total crop loss (2). A breeding program for its resistance was initiated at the University of Gezira in 1994. Twenty-one accessions were obtained from the North Central Plant Introduction Station (Ames, Iowa), and 15 breeding lines were obtained from Cornell University. Only two plants in two of the cornell breeding lines showed a high level (+8) of zucchini yellow mosaic resistance (ZYMR) (1). The first was in row 94-38 of the pedigree (91-757sib PJR + ZYMR pepo). The second was in row 94-37 of the pedigree (91-720-2self,Nigerian local. BC2 cas. F2 ZYMR.EPS). That level of resistance was retained in the F1 progenies when crossed with the popular susceptible cv, Eskandarany (Esk.) (95-13 and 95-14). Approximately 10% of the F2 plants had a ZYMR level similar to that of the donor parents (1). The F2 of 95-14 appeared to be the most promising for selection of highly resistant plants with a ZYMR level similar to that of the donor parent.

The F2 and their derived F3 populations were evaluated for ZYMR using a scale of 1 – 9 where 1 is susceptible and 9 is resistant. Mechanical inoculation with specific isolates (Su19 and E9) was used to test for ZYMR. Tissue immuno-blot assay was used to detect the presence of the virus. F2 and F3 populations were also evaluated for some horticultural characteristics such as plant vigor, stem color, leaf shape, leaf lobes, earliness and fruit characters at harvest.

Two plants in the F2 population, namely 96-12-12 and 96-69-1 obtained by selfing of 95-14, showed a high level of resistance to ZYMV (=8). The F3 derived from selfing of the two plants was artificially inoculated at INRA, Montfavet, France with the Sudanese isolate Su19 and a high intermediate level of resistance was observed (=6-7) in both progenies. Plant 96-12-12 was a very vigorous plant, intermediate in flowering and was very productive. The same F3 was planted again in the field in Sudan in row 97-6 for the progeny of 96-12-12 and a high level of ZYMR was observed )=8) when artificially inoculated at INRA, Montfavet, France with French isolate E9, which is similar to isolate Su19 in aggressiveness. The same F4 progeny was planted again in the field in Sudan in row 98-10 and a high uniform level of resistance was observed (=9). The fruit of plant 97-6-10 at harvest was cylindrical in shape, green in color and was one kilogram in weight at maturity (45 days after pollination).

Another selection in the F5, 97-20-1, which was derived from the F1 95-14, showed a high uniform level of resistance (=8) when artificially inoculated at INRA, Montfavet, France with the French isolate E9. A larger population of its F6 (98-11 to 98-20) was tested in the field in sudan and a high uniform level of resistance was observed (=9). Plants of this line are vigorous, with lobed leaves, light green fruits and resistant to powdery mildew.

The F2 population that was utilized for selection was a large segregating population (522 plants). A chi square test significantly deviated from the one gene model (1:2:1). The inheritance of resistance has been reported to be a single incomplete dominant gene that controls ZYMR (3,4) possibly affected by modifying genes (5).

This work succeeded in the fixation of two lines having a high level of ZYMR and desirable horticultural characteristics. One line (97-6-10self) is now at the F4 and the other (97-20-1self) is now at the F6.

Acknowledgement. The authors wish to thank H. Lecoq and M. Pitrat at INRA. Montfavet, France for their cooperation and encouragement.

Literature Cited

  1. Ahmed, E.A., A.E. El Jack, A.M. Salama and G.A. Dafalla. 1996. Resistance to three isolates of zucchini yellow mosaic virus (ZYMV) in squash(Cucurbita pepo L.) Cucurbit Genet. Coop. Rept. 19-81-82.
  2. Ali, H.M. 1993. Studies on some mosaic-inducing viruses in cucurbits in the Gezira. M.Sc. Thesis. University of Gezira, Wad Medani, Sudan.
  3. Munger, H.M. and R. Provvidenti. 1987. Inheritance of resistance to zucchini yellow mosaic virus in Cucurbita moschata. Cucurbit Genet Coop Rept. 10:80-81.
  4. Paris, H.S., S. Cohen, V. Burger and R.Yodrph. 1988. Single gene resistance to zucchini yellow mosaic virus in Cucurbita moschata. Euphytica 37:27-29.
  5. Robinson, R.W., N.F. Weeden and R. Provvidenti. 1988. Inheritance of resistance to zucchini yellow mosaic virus in the interspecific cross Cucurbita maxima x Cucurbita ecuadorensis. Cucurbit Genet. Coop. Rept. 11:74-75.