Linkage Mapping in a Watermelon Population Segregating for Fusarium Wilt Resistance

Isozyme, randomly amplified polymorphic DNA (RAPD), and simple sequence repeats (SSR) markers were used to generate a linkage map in an F 2 and F 3 watermelon [ Citrullus lanatus (Thumb.) Matsum. & Nakai] population derived from a cross between the fusarium wilt ( Fusarium oxysporum f. sp. niveum ) susceptible `New Hampshire Midget' and resistant PI 296341- FR . A 112.9 cM RAPD-based map consisting of 26 markers spanning two linkage groups was generated with F 2 data. With F 3 data , a 139 cM RAPD-based map consisting of 13 markers covering five linkage groups was constructed. Isozyme and SSR markers were unlinked. About 40% to 48% of the RAPD markers were significantly skewed 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-assisted selection program.