Genetic variability of fruit characteristics in Kiyomi tangor progenies of citrus
Combrink, Nicola Kim
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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.
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