Genome size variation in pumpkin (Cucurbita sp.)

Abstract

Pumpkins, a subgroup of the domesticated Cucurbita species, have been reported to range in fruit type (related to size) from miniature (<100 g) to jumbo (>273 kg). In order to obtain a wide range of fruit types it is hypothesised that all potential factors affecting fruit type must be used. One factor that is often overlooked in plant studies is genome size. In various plant species, genome size variation has been associated with characteristics such as cell size, plant size and flowering time. Such characteristics are referred to as nucleotypic parameters. In order to determine if nucleotypic selection is occurring in pumpkin, 17 varieties were analysed for genome size variation in two separate experiments. The species selected encompass the total range of fruit types reported in pumpkin. Significant nuclear DNA content variation was observed in pumpkin. There was no significant correlation between genome size and fruit type. In fact, the miniature pumpkin types were found to have the same genome size as the jumbo pumpkin types. In addition, a positive correlation between genome size and stomata length (an estimate of cell size in plants) was observed. Both the miniature and jumbo types were observed to have the smallest genome size and the smallest cell size. Thus, nucleotypic selection does appear to occur in pumpkin and appears to be involved in determining fruit type, although it may not be the only factor involved.

Genome Size of Three Miscanthus Species

“…Stomata length has been associated with nuclear DNA content (Tatum et al 2006). This is due to the relationship between cell size and nuclear DNA content (Bennett 1972).…”

“…Ten stomata were measured per slide, three slides were examined per leaf and three leaves were examined per variety. Calibrations of all measurements were done according to Tatum et al (2006). Statistics were run as previously described above.…”

“…This does not mean however, that all diploid varieties of a M. sacchariflorus have the identical nuclear DNA content. Intraspecific DNA content variation has been observed in various plant species (Rayburn et al 1989;Chung et al 1998;Wetzel and Rayburn 2000;(Rayburn et al 2004;Tatum et al 2006). Accessions of M. sacchariflorus, M. sinensis, or M. x giganteus could exist now or in the past that had a nuclear DNA content that would more precisely match the predicted nuclear DNA content of M. x giganteus.…”

The making of giant pumpkins: how selective breeding changed the phloem of Cucurbita maxima from source to sink

“…), giant pumpkins do not exhibit higher ploidy in their vegetative material or fruit (Tatum et al . ; Nakata et al . ).…”

“…Giant pumpkins (Cucurbita maxima Duchesne) are a benchmark of competitive fruit growing because of their overall size and their increase in size in the last 100 years (Hu et al 2011). Different than many other large agricultural fruits (Nátrová & Nátr 1993;Chevalier et al 2014), giant pumpkins do not exhibit higher ploidy in their vegetative material or fruit (Tatum et al 2006;Nakata et al 2012). All competitively grown pumpkins are derived from Hubbard squash that was brought to the United States in the late 1700s and originated in temperate regions of Argentina (Sanjur et al 2002).…”