Genetic linkage map for watermelon (Citrullus lanatu var. lanatus) useful in identifying DNA markers associated with bacterial fruit blotch resistance
Carter, Louisa Grant
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Bacterial fruit blotch (BFB) is a cucurbit-specific disease caused by Acidovorax avenae subsp. citrulli, a seedborne bacterium. BFB has been known to cause losses as high as 80% in some watermelon crops and poses a serious threat to cucurbit crops. The objectives of this study were to: 1) examine if BFB-resistance exists in BC2S1 plants derived from a wide cross between a BFB-resistant Plant Introduction 494817 (Citrullus lanatus var. citroides; donor parent) and the watermelon cultivar ‚ÄúCrimson Sweet‚Äù (Citrullus lanatus var. lanatus; recurrent parent), 2) examine the segregation of markers in the BC2S1 population and determine if the markers are segregating in a normal (Mendelian) fashion that can be useful for establishing inheritance of BFB-resistance in watermelon, and 3) construct an initial linkage map for watermelon using the BC2S1 population and identify putative genomic regions (loci) that may be associated with BFB-resistance. DNA extraction and isolation, sequence related amplified polymorphism (SRAP) markers, and linkage analysis were utilized to construct the initial linkage maps (using the mapping programs JoinMap(TM) 3.0 and MultiPoint). This study is useful in that few linkage maps exist for watermelon. These maps are based on testcross or BC1 populations derived from a wide cross, none of which are exhaustive or are for an advanced BC2S1 population (C. lanatus var. citroides x C. lanatus var. lanatus). Also, it is informative with respect to inheritance and segregation of DNA markers in an advanced backcross population (BC2S1) derived from interspecific crosses between wild and cultivated watermelon.