Genetic variability for yield and quality characteristics in South African pumpkin (Cucurbita maxima Duch.)

[摘要] English: The objective of this study was to study the inheritance of agronomicand quality characteristics in South African pumpkin germplasm and toidentify characteristics that could be improved through hybrid breeding.2. Six parental lines were crossed. The parents with the 15 F1-crosseswere planted in Greytown as a randomized block design with sixreplications. Three of the replications were used for destructivemeasurements at the flowering stage, while the other three were usedto evaluate yield and quality characteristics at a mature harvestingstage.3. Significant phenotypic differences were found among the parental linesand their F1-offsprings for all the characteristics evaluated. C was thesuperior parent in nine of the 19 characteristics measured. For yield,fruit number, LPL, LBL and MBT parents in general tend to have alower ranking than the crosses. The opposite was noticed for STwhere the pure breeding parents performed better.4. Specific combining abilities were calculated to be significant for all thecharacteristics, indicating that general combining ability predictedperformances deviated from the observed performances for some ofthe crosses.5. The calculated percentage variation due to GCA indicated that for mostof the characteristics mostly additive variance influenced theexpression of the characteristic. For LPL, yield, fruit mass, fruit number,ST, TT and MBT a large percentage (>25%) of the variation wereinfluenced by non-additive gene action.Very high broad sense heritabilities were calculated for all the traits.The lowest value was calculated for OBES (0.81). Very high narrowsense heritabilities were calculated for W, ML, TL, W:ML, SHT, BT,density, OW:L, OTT and OST. Heritabilities for fruit mass, LBL, ST, TTand OBES were calculated to be high. Moderate heritabilities werecalculated for yield, fruit number, LPL and MBT.7. Ovary and leaf morphology showed strong phenotypic and genotypiccorrelations with fruit characteristics expressed at a mature stage.OW:L and OST had respectively genetic correlations of 0.87 and 0.91with SHT. OTT had a genetic correlation of 0.90 with density. Densityhad negative correlations with LPL (-0.94) and LBL (-0.85).8. The highest direct response to selection was calculated for fruit mass,which showed a 122.88% improvement on the population mean. Directselection response for density was calculated to be 98.74%. For mostcharacteristics it was concluded that gain through indirect selectioncould be as successful as with direct selection.9. Positive mid-parent heterosis and high parent heterosis werecalculated for all characteristics except ST that showed only negativeHPH. Yield (-11.30 to 88.21 %), fruit mass (-58.90 to 94.05%), fruitnumber (-57.12 to 11.56%) and density (-41.64 to 93.81 %) wereidentified to express the highest heterosis in the trial.

[发布机构] University of the Free State