540 J. AMER. SOC. HORT. SCI. 127(4):540–544. 2002. J. AMER. SOC. HORT. SCI. 127(4):540–544. 2002. Marker Saturation of the Region Flanking the Gene NSV Conferring Resistance to the Melon Necrotic Spot Carmovirus (MNSV) in Melon Mónica Morales Departament de Genètica Vegetal, IRTA, Carretera de Cabrils s/n, 08348 Cabrils, Barcelona, Spain Marisol Luís-Arteaga and José María Álvarez Servicio de Investigación Agroalimentaria (SIA), Diputación General de Aragón, Apartado 727, 50080 Zaragoza, Spain Ramon Dolcet-Sanjuan Departament de Genètica Vegetal, IRTA, Carretera de Cabrils s/n, 08348 Cabrils, Barcelona, Spain Amparo Monfort Institut de Biologia Molecular de Barcelona, CID, CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain Pere Arús and Jordi Garcia-Mas 1 Departament de Genètica Vegetal, IRTA, Carretera de Cabrils s/n, 08348 Cabrils, Barcelona, Spain ADDITIONAL INDEX WORDS. Cucumis melo, bulked segregant analysis, disease resistance ABSTRACT. The recessive allele (nsv) of the NSV gene confers resistance to the Carmovirus melon necrotic spot virus (MNSV) in melon (Cucumis melo L.). Using an F 2 population obtained from the cross between the resistant Korean accession PI 161375 and a susceptible line of ‘Piel de Sapo’, we have mapped the NSV locus to linkage group 11 (G11) of the melon genome. Additional markers closely linked to NSV were developed by bulked segregant analysis (BSA) using a doubled haploid progeny population derived from the same cross. A detailed map of the NSV region was constructed containing 10 markers spanning a distance of 17.7 cM. The nearest flanking markers to NSV were two amplified fragment length polymorphisms (AFLPs) (CTA/ACG-115 and CTA/ACG-120) and one random amplified polymorphic DNA (RAPD) (OPD08-0.80) separated by 5.9 cM. Two more markers, ACC/ACC-110 and OPX15-1.06, cosegregated with NSV. is controlled by the recessive allele (nsv) of the NSV gene (Coudriet et al., 1981) and is effective against all known strains of the virus, except for a new strain recently described (Díaz et al., 2000). Several commercial cultivars have been released that are homozygous for the nsv resistance allele. The gene has been mapped to linkage group 7 of the first genetic map of melon (Baudracco-Arnas and Pitrat, 1996) with the nearest flanking markers at distances of 13.5 and 10.7 cM. Although the pathological test used in breeding programs to detect MNSV (based on MNSV inoculation) is inexpensive and easy to perform, the availability of molecular markers closely linked to the nsv allele could speed up selection as has been shown for other traits (Tanksley et al., 1989). In melon, tightly linked markers are available for only one gene, Fom-2, that confers resistance to races 0 and 1 of Fusarium oxysporum f.sp. melonis (Wang et al., 2000; Zeng et al., 1999). Other important disease resistance genes such as Fom-1 against Fusarium oxysporum f.sp. melonis races 0 and 2, Pm-1 against the powdery mildew incited by Sphaeroteca fuliginea race 1, and nsv are not currently associated with any molecular markers. In this paper we describe the development of molecular markers linked to the NSV gene. The chromosomal location of this gene was first determined in an F 2 mapping population. Additional markers closely linked to the gene were developed with amplified fragment length polymorphisms (AFLPs) and random amplified polymorphic DNA (RAPD) markers bulked segregant analysis (BSA) (Michelmore et al., 1991) in a popula- tion of doubled haploid lines (DHLs). A detailed map flanking the NSV region was constructed consisting of 10 markers spanning 17.7 cM. Received for publication 23 Oct. 2001. Accepted for publication 1 Mar. 2002. We thank Semillas Fitó S.A. for their help with the F 2 mapping population and Matchteld Mok, David Mok, Pere Puigdomènech, and Antonio José Monforte for critically reading the manuscript. Funds for this project were provided by grant 2FD97-0286-C02-01 from the Spanish ‘Comisión Interdepartamental de Ciencia y Tecnología’ (CICYT). 1 Corresponding author; e-mail jordi.garcia@irta.es. Melon necrotic spot virus (MNSV) is a single-stranded RNA Carmovirus of the Tombusviridae family. MNSV infects cucur- bit crop species such as melons, cucumbers and watermelons, grown under greenhouse conditions, and causes severe yield loss. The virus was first described in Japan (Kishi, 1966) and later detected on greenhouse-grown melons in western regions (Gonzalez–Garza et al., 1979). MNSV can be transmitted me- chanically, by zoospores of the fungus Olpidium bornovanus, by chewing insects and through the seed (Lecoq et al., 1998). Symptoms produced by MNSV in melon include local necrotic spots on inoculated cotyledons or large necrotic lesions on systemic leaves and necrosis on stems and petioles. Severity of the symptom depends on the growing conditions and the cultivar. For example, European MNSV isolates induce systemic symp- toms in cucumber and melon only erratically. Mechanically infected melon cotyledons show necrotic spots of 2 to 3 mm in diameter 3 to 5 d after inoculation and cotyledons die 15 to 21 d after inoculation. The spread of MNSV in cultivated melon can be controlled through the use of virus-free seeds or resistant varieties. There are at least two sources of resistance to MNSV in melon: the cultivar ‘Gulfstream’ and the Korean accession PI 161375. The resistance