The genetic control of pollen fertility, pollenizing and fruit set for the Prunus domestica L. plum cultivars

The plum cultivars grown in Romania are mostly from P. domestica L. and are hexaploid (6x). The research carried out on 20 cultivars emphasized presence of different genetic systems concerning pollen fertility and fruit set (male sterility, gametophytic incompatibility system and sporophytic incompatibility system). 12 of most valuable plum cultivars from Romania are male-sterile (the maternal genitor being 'Tuleu gras') and obviously need pollenizers. The male sterility is induced (indirect male sterility) and is due to the mutation, which cause modification at the component organs of the androceus before pollen formation. These mutations are fixed and inherited on material line to the offspring. The gametophytic incompatibility genetic system is present at the plum cultivars but, because there are 3 component genomes (D1D2C), each genome with one gene control and probably with multiple alleles, it is difficult to find the same allelic formula for two cultivars. Therefore, any plum cultivar with fertile pollen can pollenize any other cultivar but in different grades. Self-pollination is present to some cultivars but there are large percentile variations from one year to another. Can be considered as complementary to the allogamic pollination for 'Gras ameliorat', 'Anna Spath', 'Mirabelle de Nancy', 'Agen 707' (8,2-14,6). The sporophytic genetic incompatibility system is present to the plum cultivars but, because of the complex action of the three genomes and the reaction contact with the cells of style cannot emphasize eventually incompatibility groups (with the exception of those caused by the anatomical-morphological differences and functionality between cultivars). The best pollenizers for the majority of plum cultivars proved to be 'Anna Spath', 'Stanley', 'Mirabelle de Nancy', 'Agen 707' and 'Bluefre'.