Isozymes as molecular markers for gametophytic selection-preferential transmission in apples (Malus domestica Borkh.) V. CHOULIARAS, I. THERIOS, A. MOLASSIOTIS and G. DIAMANTIDIS Abstract In order to investigate the use of isozymes of glutamic oxalate transferase (GOT; EC 2.6.1.1), peroxidase (PRX; EC 1.11.1.7) and phosphoglycomutase (PGM; EC 5.4.2.2) as markers for gametophytic selection, cross-fertilization of two apple cultivars ('Cox' and 'Fallstaff') with 'Early Victoria' was performed at two temperatures (5 and 20°C). GOT-2 locus could be used as a marker for gametophytic selection, while under certain circumstances, PRX-2 locus could be used as a marker for preferential transmission. Deviations from the expected genotypes due to the rate of pollen elongation at relatively low or high temperatures could be detected by the GOT-2 isozymes profile but not by the PRX-2 profile. The observed segregation of two apple progenies (E 508: 'Fiesta' x SA572/2 and E 513: 'Fiesta' x 'Priscilla') in the zone of phosphoglycomutase (PGM-I) was deviated from the expected 1:1 ratio at 20°C. Since our results concerning PGM are in agreement with those of other authors studying the above zone, it could be assumed that, Pgm-1 could be used as a marker for preferential transmission.   < back .