Maternal imprinting effect on B chromosome transmission in rye

A new feature affecting the transmission rate of rye B chromosomes is described. Progenies of 0B × 2B, 2B × 0B and 2B × 2B crosses were studied, considering both the B chromosome number of the plants crossed and that of their maternal parents. A remarkably large variation within these progenies was observed. The variation found in 0B × 2B crosses was mainly due to the effect of the maternal parent of the males and females involved: pollen grains formed in 2B plants whose maternal parent had 2Bs transmitted B chromosomes at high frequency; 0B plants whose maternal parent had 2B, accepted pollen with Bs at high frequency. Conversely, 2B males and 0B females with 0B maternal parent, formed progeny with B chromosomes at a much lower frequency. A very large variation in B chromosome frequency was also observed in progenies of 2B × 0B crosses although in this case the maternal parent of 2B females does not seem to be the cause of such variation. The observed progenies of 2B x 2B crosses fitted with expectations only when the effect of the maternal parent of the plants used for crosses was considered. The interaction between females having a 2B maternal parent with 2B pollen, and the effect of the male maternal parent was also evident in this case. It seems that 2B chromosomes produce an imprinting in plants, in such a way that all their descendants can be recognised whether they carry Bs or not. The frequency of transmission of B chromosomes is increased through the plants with a 2B maternal parent. A 0B maternal parent causes the transmission frequency to decrease. We believe that these interactions have an important effect at the population level on the maintenance of the polymorphism for B chromosomes.