Inheritance of 2n pollen formation in an F₁ and F₂ population of Begonia hybrids

Inheritance of 2n pollen formation was investigated in progenies of B. ‘Orococo’ by analysing the microsporogenesis and pollen size, which is correlated to the ploidy level. After crosses between B. ‘Orococo’, B. ‘Art Hodes’ and B. soli-mutata, an F1 progeny of 359 seedlings was established of which 298 were triploid and 61 diploid. All 50 analysed triploid seedlings produced a variable frequency of monads, dyads or triads. Consequently, all triploid seedlings produced large putative 2n pollen, except for those which had formed no pollen or only bad pollen. In contrast, only 14 of the 31 diploid seedlings investigated had formed monads, dyads or triads; 11 seedlings produced only tetrads or polyads. The remaining six seedlings formed no pollen mother cells at all. F2 progeny of 15 tetraploid seedlings was established by using a triploid seedling that produced unreduced pollen as the pollinator. Of the 10 tetraploid seedlings analysed, 8 produced a variable frequency of monads, dyads or triads while 2 did not. One of these 2 seedlings, which produced only normal n gametes, was self-pollinated and resulted in a F3 population of 121 tetraploid seedlings. The results show that the inheritance of 2n pollen is very high and is probably modulated by one dominant gene and some modifier genes.