Zucchini yellow mosaic virus (ZYMV) is an important disease of Cucurbita
worldwide. Resistant cultivars are the best means of control. ZYMV resistance is
quantitative in the wild species C. ecuadorensis, and is controlled by at least three genes
in tropical C moschata. Very little molecular work has been done in Cucurbita, and no
markers are available to assist in selecting for ZYMV resistance genes.
The objectives of this research were threefold: to develop molecular markers for
use in breeding for ZYMV resistance, to develop a framework map of Cucurbita, and
to transfer ZYMV resistance from C. ecuadorensis to C. maxima 'Golden Delicious'.
The identification of a DNA marker linked to ZYMV resistance from C moschata
TSIigerian Local' was attempted using random amplified polymorphic DNA (RAPD)
analysis of resistant and susceptible bulks from the crosses C moschata 'Waltham
Butternut' x CWaltham Butternut' x TSIigerian Local'). No marker consistently linked
to ZYMV resistance was identified. Marker polymorphism was 14% between the
The cross Cpepo A0449 x (A0449 x TSTigerian Local') was used as the mapping
population to construct the framework map. The completed map consists of 153 loci
in 29 linkage groups covering 1,981 cM. Approximately 75% of the Cucurbita genome
is covered. Three morphological traits, two quantitative trait loci and a putative
secondary ZYMV resistance gene have been placed on the map; an additional eight
traits and nine RAPD markers remain unlinked.
A study of the inheritance of ZYMV resistance was conducted as part of the
efforts to mark and map resistance. Resistance appears to be controlled by at least three dominant genes in C. pepo. Environment and time since inoculation affect
expression of resistance, and resistance should be treated as a quantitative trait.
Development of ZYMV-resistant 'Golden Delicious' has progressed through five
generations. In 2000, thirty-five plants were selected which were fiilly virus resistant
and had reasonable processing quality. ZYMV resistance levels throughout the project
were 31% for the F2 and 12% for the first backcross in 1998, 3% for the backcross
progeny of the 1998 selections in 1999, and 15% for the selfed progeny of the 1999
selections in 2000.
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