Vertical transmission of prunus necrotic ringspot virus by gametes in apricot

Prunus necrotic ring spot virus (PNRSV) transmission takes place in nature during flowering and pollination. It is thought to be transmitted through pollen and seeds although the exact mechanism is unknown. In a previous work, we demonstrated that in the case of nectarine, PNRSV is located inside the pollen grains, which would help to explain its vertical transmission in this tree. Experiments involving artificial pollination resulted in transmission percentages that varied from 100% in peach to 0% in cherry. In this work we study the vertical transmission of PNRSV by gametes in apricot in an attempt to understand to what extent they are involved in the high incidence of PNRSV in this crop. In order to obtain a preliminary indication about PNRSV location on the apricot pollen grains, we made dot-blot hybridisation. Unlike in nectarine, the results pointed to the presence of the virus outside as well as inside the apricot pollen grains, results that are consistent with those of other authors. When in situ hybridisation experiments were carried out in flowers the virus was found in all organs, including its presence inside pollen grains. However, not all pollen grains contained in an anther were infected indicating an irregular distribution of the virus. We also studied the germination percentage of in vitro germinated pollen grains and found that PNRSV -infected pollen have a germination rate of only 27% while healthy pollen shows 64%.