The inheritance of foreground stripe pattern in rind of watermelon fruits [Citrullus lanatus (Thunb.) Matsum. & Nakai] was evaluated and molecular markers for selecting the Jubilee-type (JT) stripe pattern were developed based on bulked segregant analysis (BSA). Divergence in rind pattern among F2 progeny derived from crossing Crimson-type (CT) 'Arka Manik' (AM) with JT 'TS34' (TS) indicated that stripe pattern is a quantitative trait controlled by more than one gene. The BSA of F2 plants (derived from a cross between 'AM' and 'TS') using 60 random amplified polymorphic DNA (RAPD) primers revealed a distinct RAPD band (AT14-900) polymorphic between 'AM' (CT) and 'TS' (JT). The AT14-900 sequence (925 bp) was blasted to the reference watermelon (97103) genome and high sequence similarity (97.8%) was identified on physical location of 26246077 to 26246993 bp on chromosome 6. Two expressed sequence tags (ESTs) designated 'wsbin6-10' and 'wsbin6-11' that were closely linked to AT14-900 on a genetic linkage map (developed using the F2 population derived from 'AM' x 'TS') were positioned 2,216 kb and 71 kb from AT14-900, respectively on the reference watermelon genome sequence. Marker genotyping of the F2 population showed that wsbin6-11 was tightly linked to the JT stripe pattern of 'TS' and could be a useful codominant marker for selecting this trait. In a test using 100 breeding lines, 34 of the 36 lines carrying the JT stripe pattern were homozygous for the wsbin6-11 marker (450 bp) derived from 'TS', while other lines (e.g., with no stripe or CT stripe pattern) were homozygous for the wsbin6-11 marker (420 bp) derived 'AM'. These results indicated that wsbin6-11 would be a useful marker in watermelon breeding programs aiming to select for the JT stripe pattern from other various foreground and background rind patterns.

Abstract:This study was performed to analyze genetic relationships of the four major cucurbitaceous crops including watermelon, melon, cucumber, and squash/pumpkin. Among 120 EST-SSR primer sets selected from the International Cucurbit Genomics Initiative (ICuGI) database, PCR was successful for 51 (49.17%) primer sets and 49 (40.8%) primer sets showed polymorphisms among eight Cucurbitaceae accessions. A total of 382 allele-specific PCR bands were produced by 49 EST-SSR primers from 24 Cucurbitaceae accessions and used for analysis of pairwise similarity and dendrogram construction. Assessment of the genetic relationships resulted in similarity indexes ranging from 0.01 to 0.85. In the dendrogram, 24 Cucurbitaceae accessions were classified into two major groups (Clade I and II) and 8 subgroups. Clade I comprised two subgroups, Clade I-1 for watermelon accessions [I-1a and I-1b-2: three wild-type watermelons (Citrullus lanatus var. citroides Mats. & Nakai), I-1b-1: six watermelon cultivars (Citrullus lanatus var. vulgaris Schrad.)] and Clade I-2 for melon and cucumber accessions [I-2a-1: 4 melon cultivars (Cucumis melo var. cantalupensis Naudin.), I-2a-2: oriental melon cultivars (Cucumis melo var. conomon Makino.), and I-2b: five cucumber cultivars (Cucumis sativus L.)]. Squash and pumpkin accessions composed Clade II {II-1: two squash/ pumpkin cultivars [Cucurbita moschata (Duch. ex Lam.)/Duch. & Poir. and Cucurbita maxima Duch.] and II-2: two squash/pumpkin cultivars, Cucurbita pepo L./Cucurbita ficifolia Bouche.}. These results were in accordance with previously reported classification of Cucurbitaceae species, indicating that watermelon EST-SSRs show a high level of marker transferability and should be useful for genetic study in other cucurbit crops.