Unreduced Gametes in Brassica: Effects of Genotype, Temperature and Interspecific Hybridization

Unreduced gametes (pollen and ovules with the somatic chromosome number) in Brassica have been frequently observed but little studied. We investigated the effects of genotype and temperature on male unreduced gamete production in the Brassica oilseed species B. napus (canola), B. juncea (Indian mustard) and B. carinata (Ethiopian mustard), and in the interspecific hybrids between them. Production of unreduced gametes by parental species ranged from 0.0 – 0.1% depending on the genotype, and was little affected by ambient temperature. However, unreduced gametes were involved in the parentage of 4 out of 60 interspecific hybrids. Interspecific hybrids produced more unreduced gametes than their parents (0.1 - 3.3% depending on genotype). These unreduced gametes comprised a large percentage of the viable pollen fraction (0.2 - 33%) in the hybrids. Cold temperatures (10°C/5°C day/night) stimulated two genotypes of B. napus × B. carinata hybrid to produce nearly tenfold more unreduced gametes (9% and 23%) than other temperature treatments (30°C/20°C, 25°C/15°C and 18°C/13°C). No other hybrid genotypes were affected by ambient temperature in producing unreduced gametes. Male unreduced gamete production in Brassica appears to be influenced by complex interactions of genotype, temperature and hybridity.