Cucurbit Genetics Cooperative Report 7:86-87 (article
Linkage between an Isozyme Locus and One of the Genes Controlling
Resistance to Watermelon Mosaic Virus 2 in Cucurbita ecuadorensis
Weeden, N.F., R.W. Robinson and F.Ignart*
Dept. Horticultural Sciences, New York Agricultural Experiment Station,
Geneva NY 14456
Resistance to watermelon mosaic virus 2 (WMV-2) has been found in Cucurbita ecuadorensis (2). The resistant phenotype
appears to be controlled by more than one locus (1), but little
is known regarding the number of loci involved or the
interactions between these loci.
As part of an on-going program to transfer multiple virus
resistance from Cucurbita ecuadorensis to C. maxima two backcross populations [(C. maxima x C.
ecuadorensis) x C. maxima] were grown in field plots
at the New York State Agricultural Experiment Station, Geneva NY.
Each plant was inoculated in the first true leaf stage with WMV-
2, and natural infection of WMV-2 also occurred in the field.
Plants were phenotyped for 12 different isozyme systems (acid
phosphatase, aldolase, aspartate aminotransferase, esterase,
galactosidase, leucine aminopeptidase, malate dehydrogenase,
phosphoglucomutase, peroxidase, shikimic dehydrogenase.
superoxide dismutase and triose phosphate isomerase), permitting
the observation of products from at least 21 segregating loci.
Correlation was found between resistance to WMV-2 and an allele
of Aldo-p, the isozyme locus specifying the plastid-
specific aldolase (3). A majority of the plants displaying a
heterozygous Aldo-p phenotype at Aldo-p were
resistant while all except one plant exhibiting the aldolase
phenotype of C. maxima (homozygous slow) were susceptible
(Table 1). We interpret these results to indicate that C.
ecuadorensis possessed a WMV-2 resistance gene closely linked
to Aldo-p. In the genetic background of the backcross
population, the possession of this gene appeared to be a required
but not a sufficient condition for expression of the resistant
phenotype. The one individual exhibiting the slow aldolase
allozyme in combination with the resistant phenotype could have
resulted from a recombination event. The considerable number of
WMV-2 susceptible plants heterozygous at Aldo-p may be due
to an absence in these plants of other genes from C.
ecuadorensis which contribute to the resistant phenotype.
All other isozyme loci appeared to be assorting randomly with
respect to WMV-2 resistance.
Table 1. Backcross segregation for watermelon mosaic virus 2
resistance and allozymes at the Aldo-D locus.
- Greber, R.S. and M.E. Herrington. 1980. Reaction of
interspecific hybrids between Cucurbita ecuadorensis, C. maxima and C. moschata to inoculation with
cucumber mosaic virus and watermelon mosaic virus 1 and 2.
Australian Plant Pathology 9:1-2.
- Provvidenti, R., R.W. Robinson and H.M. Munger. 1978.
Resistance in feral species to six viruses infecting Cucurbita. Plant Dis. Reptr. 62:326-329.
- Weeden, N.F. 1984. A nuclear gene codes for the plastid-specific
aldolase in Cucurbita species. Cucurbit Genet. Coop. Rpt.
*Present address: Institut de Recherches TEZIER,
Domaine de Maninet, Route de Beaumont, B.P. 336, 26003 Valence-