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#triploid

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Plant Breeding 4

Seedless watermelon is an example of:

Seedless watermelon is classic application of triploid sterility exploiting 3x block. Normal diploid watermelon has 2n=22. Using colchicine, breeders create tetraploid lines 4n=44 by doubling diploid seedlings and selecting fertile tetraploids. Tetraploid is then used as female parent crossed to diploid male, yielding triploid hybrid 3n=33. Triploid hybrid grows vigorously with larger leaves due to gigas effect of polyploidy but meiosis is chaotic because three homologs cannot segregate evenly, causing ovule and pollen abortion and highly sterile flowers. Fruit develops through stimulation by

Ref: Kihara H. 1951 Triploid watermelon history; Maynard DN. Watermelon breeding. USDA

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Chromosome variations

Triploid organisms have chromosome number

Euploid number is designated by multiples of the basic haploid set n. Diploid organisms carry 2n chromosomes, one set from each parent. Triploidy means three complete haploid genomes present in each somatic nucleus, denoted 3n. Triploids arise via fusion of unreduced 2n gamete with normal n gamete, failure of meiosis after fertilization, or somatic doubling in diploid tissues. Because three homologous copies cannot pair evenly at meiosis I, triploids show irregular segregation, unbalanced gametes, high sterility, and larger cell size, common in cultivated bananas and watermelons.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 8: Polyploidy Types

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