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.