Mentor pollen effect on the in-vivo germination of self-incompatible apple pollen

Investigations were carried out to ascertain to what extent “mentor pollen” can influence the performance of self pollen in apple styles. Self-incompatible ‘Starkrimson’ flowers on branches, placed at room temperature or in a growth chamber, were (1) self-pollinated, (2) cross-pollinated with compatible untreated or (3) irradiated (150 krad) ‘Golden Delicious’ pollen, or (4) pollinated with a mixture (2:1 w/w) of irradiated (mentor) pollen and self pollen. After 18 h, nearly the same proportion (> 90%) of the self-incompatible pollen had germinated on the stigma and penetrated the apical part of the style as compatible pollen. However, subsequent growth of the self-pollen tubes was inhibited. After 48 h, less than 1% had reached the stylar base as compared with 21–24% of the compatible pollen tubes. Irradiation strongly impaired pollen vitality: only 1% of the tubes had reached the base of the style after 48 h. The mixture of the irradiated mentor pollen and self pollen performed better. In this case, 6.4–9.9% of the tubes was observed in the basal part of the style, inferring that tube growth of the self pollen was significantly promoted by the mentor pollen.