Genetic variability of fruit characteristics in Kiyomi tangor progenies of citrus
Abstract
English: In a citrus breeding programme, information on the breeding value of available parents and
the heritability of specific characters can be an important aid to the breeder when planning
controlled crosses for cultivar improvement. By quantifying the genetic variation in a
population the breeder can study the relationships between the hybrids and parents and
gain an understanding of how certain characteristics are inherited. Therefore a study was
undertaken to investigate the genetic variation in the progenies of six mandarin families,
where female parent Kiyomi tangor was crossed with male parents Dancy, Hansen, Rishon,
Roma, Shani and Sunburst mandarins. Data were collected over a two year period for the
fruit quality characteristics of rind colour, fruit size, fruit shape and fruit internal quality.
A significant level of variation was found between the families for all the fruit characteristics
studied. The within family variation was larger than the between family variation and
indicated a high level of genetic variation within the families, while the within tree variation
was found to be lower than the within family variation. Data collected over a two year period
showed significant year and year x family variation for many of the fruit characteristics. The
intraclass correlation coefficient, relevant to selection within the families, was found to be
fairly low for all the fruit characteristics studied and indicated that the variation found within
the families was only partly genetic and non-genetic factors contributed to the variation in the
phenotype. Therefore only two years of testing will not be reliable and a mean performance
over multiple years data is recommended for effective selection.
All the families showed an improvement in the population for rind colour, fruit shape and the
fruit internal quality while half of the families showed an improvement for fruit size. All the
families showed heterosis with some individuals being superior to both parents. Families
with male parents Hansen, Rishon, Shani and Sunburst had a rind colour superior to the
other families, while the Kiyomi x Rishon family had larger fruit with a more round fruit shape
and the Kiyomi x Roma family had a superior internal quality. This study revealed the male
parent to have a large influence on the progeny and male parents with a deeper orange rind
colour, larger fruit size, better fruit shape and superior internal quality resulted in families
with a greater improvement in the population. Therefore only male parents of the highest
quality should be used as parents in breeding programmes in order to increase the chance
of obtaining a superior new cultivar. Afrikaans: In In sitrus teelprogram is die teelwaarde van die beskikbare teelouers sowel as die erflikheid
van spesifieke eienskappe van onskatbare waarde tydens die beplanning van gerigte
kruisings vir spesifieke teeldoelwitte. Deur die genetiese variasie in In teelpopulasie te
kwantifiseer kan die teler die verwantskap tussen kruisingsnageslag en ouers bestudeer en
sodoende meer leer oor hoe sekere eienskappe oorgeërf word. Dit is dus met dié doel dat
die genetiese variasie in die nageslag van ses mandaryn families ondersoek is waar Kiyomi
tangor as vroulike ouer gekruis is met Dancy, Hansen, Rishon, Roma, Shani en Sunburst
mandaryne as manlike ouers. Data t.o.v. die vrugkwaliteitseienskappe van skilkleur,
vruggrootte, vrugvorm en interne kwaliteit is oor In tydperk van twee jaar versamel.
Daar is betekenisvolle variasie tussen die families t.o.v. alle vrugkwaliteitseienskappe
gevind. Die variasie t.o.v. vrugkwaliteitseienskappe binne families was groter as die variasie
tussen families en dui op In hoë genetiese variasie binne families, terwyl die variasie binne In
boom kleiner was as in In familie. Data ingesameloor In tydperk van twee jaar wys In
beduidende jaar x familie variasie t.o.v die meeste vrugeienskappe. Die intraklas
korrelasiekoeffisiënt wat gebruik word vir seleksie binne families was redelik laag vir al die
vrugeienskappe wat bestudeer is. Dit dui daarop dat die variasie van 'n fenotipe sowel
geneties as nie-geneties van aard is. Twee jaar van evaluering is nie voldende nie en
evaluering oor 'n aantal jare sal meer betroubaar wees vir doeltreffende seleksie.
AI die families het In verbetering in skilkleur, vrugvorm en interne kwaliteit getoon terwyl die
helfte van die families In verbetering in vruggroote gehad het. Heterose het in al die families
voorgekom en sommige individue van die nageslag het beter vertoon as beide die ouers.
Families met Hansen, Rishon, Shani en Sunburst as manlike ouers se skilkleur was beter as
die ander families, terwyl die Kiyomi x Rishon familie groter en ronder vrugte gehad het en
die Kiyomi x Roma familie In beter interne vrugkwaliteit. Hierdie studie het getoon dat
manlike ouers In beduidende invloed op vrugeienskappe van die nageslag het en dat
manlike ouers met In dieper rooi skilkleur, groter vrugte, beter vrugvorm en beter interne
kwaliteit aanleiding gegee het tot families waarvan die nageslag In groter verbetering getoon
het. Dit is dus belangrik dat slegs manlike ouers van uitstaande kwaliteit as teelouers
gebruik moet word in In teelprogram ten einde die kanse te verhoog om In uitstaande nuwe
kultivar te verkry.
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