Linkage mapping in a watermelon population segregating for fusarium wilt resistance

Isozyme, randomly amplified polymorphic DNA (RAPD), and simple sequence rep eats (SSR) markers were used to generate a linkage map in an F-2 and F-3 wa termelon [Citrullus lanatus (Thumb.) Matsum. & Nakai] population derived fr om a cross between the fusarium wilt (Fusarium oxysporum f. sp. niveum) sus ceptible (New Hampshire Midget' and resistant PI 296341-FR. A 112.9 cM RAPD -based map consisting of 26 markers spanning two linkage groups was generat ed with F-2 data. With F-3 data, a 139 cM RAPD-based map consisting of 13 m arkers covering five Linkage groups was constructed. Isozyme and SSR marker s were unlinked. About 40% to 48% of the RAPD markers were significantly sk ewed from expected Mendelian segregation ratios in both generations. Bulked segregant analysis and single-factor analysis of variance were employed to identify RAPD markers linked to fusarium wilt caused by races 1 and 2 of F . oxysporum f.sp. niveum. Current linkage estimates between the resistance trait and the marker loci were too large for effective use in a marker-assi sted selection program.