Genetic variability for yield and quality characteristics in South African pumpkin (Cucurbita maxima Duch.)
Abstract
English: The objective of this study was to study the inheritance of agronomic
and quality characteristics in South African pumpkin germplasm and to
identify characteristics that could be improved through hybrid breeding.
2. Six parental lines were crossed. The parents with the 15 F1-crosses
were planted in Greytown as a randomized block design with six
replications. Three of the replications were used for destructive
measurements at the flowering stage, while the other three were used
to evaluate yield and quality characteristics at a mature harvesting
stage.
3. Significant phenotypic differences were found among the parental lines
and their F1-offsprings for all the characteristics evaluated. C was the
superior parent in nine of the 19 characteristics measured. For yield,
fruit number, LPL, LBL and MBT parents in general tend to have a
lower ranking than the crosses. The opposite was noticed for ST
where the pure breeding parents performed better.
4. Specific combining abilities were calculated to be significant for all the
characteristics, indicating that general combining ability predicted
performances deviated from the observed performances for some of
the crosses.
5. The calculated percentage variation due to GCA indicated that for most
of the characteristics mostly additive variance influenced the
expression of the characteristic. For LPL, yield, fruit mass, fruit number,
ST, TT and MBT a large percentage (>25%) of the variation were
influenced 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 narrow
sense heritabilities were calculated for W, ML, TL, W:ML, SHT, BT,
density, OW:L, OTT and OST. Heritabilities for fruit mass, LBL, ST, TT
and OBES were calculated to be high. Moderate heritabilities were
calculated for yield, fruit number, LPL and MBT.
7. Ovary and leaf morphology showed strong phenotypic and genotypic
correlations with fruit characteristics expressed at a mature stage.
OW:L and OST had respectively genetic correlations of 0.87 and 0.91
with SHT. OTT had a genetic correlation of 0.90 with density. Density
had 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. Direct
selection response for density was calculated to be 98.74%. For most
characteristics it was concluded that gain through indirect selection
could be as successful as with direct selection.
9. Positive mid-parent heterosis and high parent heterosis were
calculated for all characteristics except ST that showed only negative
HPH. Yield (-11.30 to 88.21 %), fruit mass (-58.90 to 94.05%), fruit
number (-57.12 to 11.56%) and density (-41.64 to 93.81 %) were
identified to express the highest heterosis in the trial. Afrikaans: Die doel van die studie was om die oorerwing van agronomiese en
kwaliteitseieskappe in Suid-Afrikaanse pampoenkiemplasma te
bestudeer.
2. Ses ouerlyne is in In dialleelontwerp gekruis. Die ses ouers asook die
15 F1-kruisings is in Greytown geplant. Die proef is geplant as In
gerandomiseerde blokontwerp met ses herhalings. Drie herhalings is
vir destruktiewe waarnemings tydens blomstadium gebruik. Die
oorblywende drie herhalings is gebruik vir die evaluering van opbrengsen
kwaliteitseienskappe na oes, nadat die vrugte volwassenheid bereik
het.
3. Vir beide die ouerlyne en F1-kruisings is betekenisvolle verskille
bereken vir gemideldes van alle eieskappe. C was die beste ouer vir
nege van die 19 eienskappe wat geëvalueer is. Vir opbrengs,
vrugaantal, LPL, LBL en MBT het die ouers oor die algemeen swakker
presteer as die kruisings. Die teenoorgestelde is waargeneem vir ST
waar die suiwertelende ouers beter presteer het.
4. Die berekende spesifieke kombineervermoë was betekenisvol vir alle
eienskappe. Dit wil sê die voorspelde voorkomste het afgewyk van die
waargeneemde voorkomste.
5. Die berekende persentasie variasie as gevolg van algemene
kombineervermoë het aangedui dat die meeste van die eienskappe se
uitdrukking hoofsaaklik deur additiewe variansie beïnvloed word. Vir
LPL, opbrengs, vrugmassa, vrugaantal, ST, TT en MBT is In groot
persentasie (>25%) van die variasie veroorsaak deur nie-additiewe
geenwerking.
Baie hoë waardes vir erflikheid in die breë sin is vir alle eienskappe
bereken. Die laagste waarde is vir OBES (0.81) bereken. Baie hoë
waardes vir erflikheid in die nou sin is vir W, ML, TL, W:ML, SHT, BT
digtheid, OW:L, OTT en OST bereken. Hoë erfbaarhede vir
vrugmassa, LBL, ST, TT en OBES is ook bereken. Erfbaarhede vir
opbrengs, vrugaantal, LPL en MBT is bereken as matig.
7. Vrugbeginsel- en blaarmorfologie het sterk fenotipiese en genotipiese
korrelasies getoon met vrugeienskappe wat op "n volwasse stadium
uitgedruk word. OW:L en OST het afsonderlik genetiese korrelasies
van 0.87 en 0.91 met SHT getoon. OTT het "n genetiese korrelasie van
0.90 met digtheid gehad. Digtheid was negatief gekorreleerd met LPL
(-0.94) en LBL (-0.85).
8. Die hoogste direkte seleksie respons is bereken vir vrugmassa, wat "n
122.88% verbetering op die populasie gemiddeld tot gevolg gehad het.
Direkte seleksie respons vir digtheid was 98.74%. Vir meeste
eienskappe kon afgelei word dat verbetering deur indirekte seleksie net
so suksesvol kan wees as met direkte seleksie.
9. Positiewe mid-ouer en beter-ouer heterose is bereken vir alle
eienskappe behalwe vir ST wat net negatiewe beter-ouer heterose
getoon het. Opbrengs (-11.30-88.21 %), vrugmassa (-58.90-94.05%),
vrugaantal (57.12-11.56%) en digtheid (-41.64-93.81 %) het die meeste
heterose in die proef getoon.