139 The Genetic Control of Pollen Fertility, Pollenizing and Fruit Set for the Prunus domestica L. Plum Cultivars M. Botu, C. Şarpe and S. Cosmulescu I. Botu Faculty of Horticulture Fruit Growing Research & Extension University of Craiova Station (SCDP) Vlcea 13, Al. I. Cuza str. 464, Calea lui Traian str., Craiova 1100 Rm. Vlcea 1000 Romania Romania Keywords: plum, genetic control, male sterility Abstract: 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 (D 1 D 2 C), 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 Späth’, ‘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 Späth’, ‘Stanley’, ‘Mirabelle de Nancy’, ‘Agen 707’ and ‘Bluefre’. INTRODUCTION Genetic nature processes control the pollination of Prunus domestica L. cultivars, also pollination is influenced by the environmental conditions and pollenizing vectors (insects, in our case). The genetic control systems of pollen fertility and pollenizing are economically determinant because they influence in a direct way to the fruit production. The plum cultivars grown in Romania are included into Prunus domestica L. and Prunus insititia L. species. All the plum cultivars for fresh consumption belong to Prunus domestica L. and are hexaploid (2n=6x) and have the following genetic formula D 1 D 1 D 2 D 2 CC. In the case of the plum cultivars different types of genetic systems concerning male sterility are known: gametophytical incompatibility system (Schaer, 1926; Misic, 1956; Tarnavski et al., 1963; Bumbac, 1975; etc.) and sporophytical incompatibility system (Hugs and Babcock, 1950; Botu M., 2000). Sears (1947) considered that male sterility is caused by a mutation on one of the loci responsible of pollen formation and classified the male sterility depending on the place of action: nuclear genetic sterility, cytoplasmatic sterility and cytoplasmatic-genetic sterility. Correns (1904), Wettstein (1924) and Michaelis (1954) established that pollen sterility is caused by plasmagenes. The gametophytic incompatibility system is generated by three types of Proc. 7 th IS on Plum & Prune Genetics Eds. V. Djouvinov et al. Acta Hort. 577, ISHS 2002