Theor Appl Genet (1986) 72:274-278 9 Springer-Verlag 1986 Linkage relationships of 19 protein coding genes in watermelon N. Navot and D. Zamir The Hebrew University of Jerusalem, The Faculty of Agriculture, Department of Field and Vegetable Crops, P.O. Box 12, Rehovot 76-100, Israel Received November 11, 1985; Accepted December 16, 1985 Communicated by D. von Wettstein Summary. Segregation of seed proteins and isozymes was analysed in two Citrullus crosses. In the first cross an F1 hybrid between C. lanatus and the wild species C. colocynthis was used as a female parent in a back- cross to C. lanatus. In this interspecific cross the segregation of 17 markers was analysed. Four linkage groups were identified: linkage group 1 includes the genes Est-2, Skdh-2, Tpi-1, Fdp-1, Sod-1 and Prx-1; linkage group 2 - Got-l, Got-2 and Sp-4; linkage group 3 - Pgm-1 and Gdh-2; linkage group 4 with Pgi-1 and Pgi-2. In the second cross an F1 hybrid between two C. colocynthis accessions was backcrossed to one of its parents. Seven loci were scored and no new linkages were found. Key words: Citrullus - Isozymes - Seed proteins - Linkage Introduction The genus Citrullus of the Cucurbitaceae family in- cludes three diploid species (2n=22) originating in southern Africa (Jeffrey 1975). The cultivated water- melon C. lanatus is of a world-wide distribution; the wild species C. colocynthis is found mainly in northern Africa and Asia (Zamir et al. 1984) while C. ecirrhosus is restricted to the Namibian desert (Meeuse 1962). Twenty-five genes have been described in watermelon, most of them affecting the morphology and color of fruit and seed (Robinson et al. 1976). In comparison with the genetic information about other economically important crops the watermelon has been somewhat neglected. We describe here segregation patterns and linkage relationships of two seed protein and seventeen isozymic genes in Citrullus. Materials and methods Plant material The following Citrullus accessions were used for the crosses: C. colocynthis-lO from the coastal plain of Israel, C. coloeyn- this-2 from the Sinai desert, and a local cultivar, C. lanatus-60 'Mallali' (Zamir et al. 1984). Two backcrosses were analysed: in the first, the interspecific F1 hybrid between C. lanatus-60 and C. colocynthis-lO was used as the female parent in a cross with C. lanatus-60 as the pollen parent. This cross will be referred to as cross I. In the second cross (cross II) the intra- specific F1 hybrid between C. coloeynthis-lO and C. colocyn- this-2 was used as the pollen donor in a cross with C. coloeyn- this-2. Each seed from the backcross generations was cut in half; the cotyledon section was used for extraction of total seed proteins and the radicle section for sowing. Halved seeds were dipped in an antifungal powder mixture (Captan+PCNB 1 : 1) and germinated in the dark in vermiculite-covered trays at a temperature of28-32 ~ After 24 h the germinating seeds were treated with the same antifungal mixture and transferred to seedling trays filled with a 1:1 mixture of peat and vermiculite. Seedlings were grown in the greenhouse and fertilised weekly with half-strength Hoagland's solution. Electrophoresis SDS polyacrylamide gel electrophoresis (PAGE) for the ana- lysis of seed proteins was carried out using 18% bis-acrylamide gels. Extraction of proteins, preparation of gels, running condi- tions, staining and destaining were according to Galili and Feldman (1983). Isozymes were subjected to starch gel electrophoresis using crude extracts obtained by macerating 1 cm 2 leaf discs on ice in one of the following three buffers: buffer A and buffer B, both prepared according to Zamir and Ladizinsky (1984), and buffer C containing 0.2 M KH2PO4 (pH 7.5), 0.1 M 2-mercaptoethanol and 12% PVP-40. Three different gel and electrode buffer systems were used to resolve the enzyme bands. System 1 was a Tris citrate/ lithium borate mixture (Gottlieb 1981) which was used to assay the following enzymes extracted with buffer A: glutamate oxaloacetate transaminase (GOT), superoxide dismutase