Abstract
As part of our ongoing efforts to sequence and map the watermelon (Citrullus spp.) genome, we have constructed a high density genetic linkage map. The map positioned 234 watermelon genome sequence scaffolds (an average size of 1.41 Mb) that cover about 330 Mb and account for 93.5% of the 353 Mb of the assembled genomic sequences of the elite Chinese watermelon line 97103 (Citrullus lanatus var. lanatus). The genetic map was constructed using an F8 population of 103 recombinant inbred lines (RILs). The RILs are derived from a cross between the line 97103 and the United States Plant Introduction (PI) 296341-FR (C. lanatus var. citroides) that contains resistance to fusarium wilt (races 0, 1, and 2). The genetic map consists of eleven linkage groups that include 698 simple sequence repeat (SSR), 219 insertion-deletion (InDel) and 36 structure variation (SV) markers and spans ∼800 cM with a mean marker interval of 0.8 cM. Using fluorescent in situ hybridization (FISH) with 11 BACs that produced chromosome-specifc signals, we have depicted watermelon chromosomes that correspond to the eleven linkage groups constructed in this study. The high resolution genetic map developed here should be a useful platform for the assembly of the watermelon genome, for the development of sequence-based markers used in breeding programs, and for the identification of genes associated with important agricultural traits.
Highlights
Watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] is an important specialty crop accounting for,7% of the agricultural area devoted to vegetable crops (FAO, 2009)
303 InDels and 54 structure variation (SV) were selected for polymorphism analysis between the two recombinant inbred lines (RILs) parents
We described the construction of a watermelon genetic map utilizing polymorphic simple sequence repeat (SSR), InDel and SV markers derived from whole genome sequencing and re-sequencing, including scaffold anchoring and orientation
Summary
Watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] is an important specialty crop accounting for ,7% of the agricultural area devoted to vegetable crops (FAO, 2009). Because of many years of cultivation and selection for watermelon of desirable qualities, the modern watermelon cultivars share a narrow genetic base, and are susceptible to a large number of diseases and pests [1]. There is a continuous need to develop new watermelon varieties with enhanced disease and pest resistance and with enhanced fruit quality, suitable to consumer needs. The watermelon includes several subspecies with a wide genetic diversity that could be a useful germplasm sources for improving watermelon cultivars [1]. Several critical steps that include accurate phenotyping for disease or pest resistance, genetic mapping and genome sequencing and assembly studies are needed as part of continuous efforts of exploring and utilizing watermelon germplasm for the improvement of watermelon cultivars. There is a need for a cytogenetic map that could be useful in the identification of watermelon chromosomes and demarcating possible structural differences between the cultivated watermelon and it’s related Citrullus spp
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