A genetic linkage map for watermelon based on randomly amplified polymorphic DNA markers

A genetic linkage [randomly amplified polymorphic DNA (RAPD)-based] map was constructed for watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] u sing a BC1 population [PI 296341-fusarium wilt resistant x New Hampshire Mi dget (fusarium susceptible)] x 'New Hampshire Midget'. The map contains 155 RAPD markers, and a 700-base pair sequenced characterized amplified region (SCAR) marker that corresponds to a fragment produced by the RAPD primer G TAGCACTCC. This marker was reported previously as linked (1.6 cM) to race 1 fusarium wilt resistance in watermelon. The markers segregated to 17 linka ge groups. Of these, 10 groups included nine to 19 markers, and seven group s included two to four markers. The map covers a genetic linkage distance o f 1295 cM. Nine of the 10 large linkage groups contained segments with low (or no) level of recombination (0 to 2.6 cM) among markers, indicating that the watermelon genome may contain large chromosomal regions that are defic ient in recombination events. The map should be useful for identification o f markers linked closely to genes that control fruit quality and fusarium w ilt (races I and 2) resistance in watermelon.