| With the ever-increasing demand of healthy vegetable oil and its other products for domestic and industrial use,there is the need to seek for alternative sources through molecular breeding to meet this demand.Recently,the Cleaved Amplified Polymorphism Sequence(CAPS)markers had emerged as a powerful source for molecular breeding.Two watermelon accessions named as P 1 = W1-1(low oil percentage),P 2 = PI-186490(high oil percentage)and with their F1 and F2:3 were used for measuring seed oil percentage,also other seed phenotypic traits(seed length,seed thickness,seed width,thickness of seed coat,100 seed weight).Mean of seed oil percentage(SOP)in PI-186490(mean = 22.25%)was significantl y higher than that of W1-1(mean = 14.75%).The F2:3 seeds had seed oil percentage ranging from 9% to 32%.Means of other seed traits in P 1 and P2 were: seed length(8.81 mm and 14.71 mm),seed width(5.96 mm and 10.53 mm),seed coat thickness(2.06 mm and 2.65 mm),thickness of seed coat(0.33 mm and 0.15 mm)100 seed weight(4.70 g and 18.20 g).Overall,145 CAPS markers with six restriction endonucleases(Bam HI,Eco RI,Hind II,Hind III,Hinf I,Pst I)were applied to the F2 population for molecular genotyp ing.The linkage map spanned a distance of 3000.19 c M covering the whole genome with an average distance of 20.01 c M.Total of 11 QTLs were detected as follows;seed length(2 QTLs),seed width(1 QTL),seed thickness(1 QTL),thickness of seed coat(4 QTL s),100 seed weight(2 QTLs),seed oil percentage(1 QTL).The LOD score ranged from a minimum value of 2.51 to a maximum of 36.60.The PVE values for all the detected QTLs were from 3.11% to 47.55%.The total variation effect for the detected seed length Q TLs on chromosomes 6 and 10 was 51.35%.The only QTL for seed width mapped to chromosome 6 had a variation effect of 45.91%.The variation effect for seed thickness QTL on chromosome 4 was 7.88%.Three chromosomes(1,3 and 6)played host to the thickness of seed coat QTLs with a total variation effect of 58.83%.The total variation effect for 100 seed weight QTLs on chromosomes 6 and 10 was 39.76%.The only QTL for seed oil percentage mapped on chromosome 6 recorded variation effect of 14.44%.QTLs for See d Length,Seed Width,Thickness of Seed Coat and 100 Seed Weight(q SL-6-1,q SW-6-1,q TSC-6-1,q100SWT-6-1)were all located on chromosome 6 within a less than 5 c M of genetic distance indicating colocalization.Physicochemical properties of P 1 and P2 oils were analysed in this study as well.Five main fatty acids(FAs)were detected namely: palmitic acid(16:0),stearic acid(18:0),oleic acid(18:1),linoleic acid(18:2),?-linolenic acid 18:3).W1-1,fatty acids percentage increased from ?-linolenic acid(1.09%)to stearic acid(10.48%)to palmitic acid(20.50%)to linoleic acid(26.80%)to oleic acid(27.04%),whiles in PI-186490 it increased from ?-linolenic acid(0.29%)to stearic acid(10.80%)to palmitic acid(13.36%)to oleic acid(16.83%)to linoleic acid(40.37%).Correlation between the various fatty acids and seed oil percentages(SOP)were examined to understand possible relationship that may exist.Significant difference was observed in SOP and concentration of most fatty acids.Other properties examined were acid value(mg KOH/g),free FAs(%),oxidizability value(Cox),saponification value(mg KOH/g),unsaponifiable matter(%),specific gravity(25°C).The results of watermelon seed oil properties compared with standards set for edible and industrial oil sources,confirmed the stability,edibility,industrial and economic potentials for watermelon seed oil.The data on seed oil percentage and detected QTLs presented by this study will provide very practical information for future breeding and genetic schemes in watermelon. |
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