STUDIES OF POLLEN GRAIN GERMINATION, POLLEN-TUBE GROWTH, MICROPYLAR PENETRATION AND SEED SET IN INTRASPECIFIC AND INTERGENERIC CROSSES WITHIN 3 CRUCIFERAE SPECIES

Pollen grain germination, pollen tube growth and micropylar penetratio n were investigated in intraspecific and intergeneric crosses involvin g Brassica napus L. ssp. oleifera (Metzg.) Sinsk. (oil-seed rape or fo dder rape), xBrassicoraphanus Sageret (Raparadish) and diploid (2x) an d tetraploid (4x) accessions of Sinapis alba L. (white mustard). For t he reciprocal intergeneric crosses between R napus and xBrassicoraphan us no effective barriers to pollen tube growth on stigmata or in style s were observed. The resulting low frequency of hybrid plants was main ly associated with a low rate of ovules with micropylar penetration pe r siliqua or with embryo abortion. Hybrid plants could be obtained wit hout use of embryo rescue. In reciprocal crosses between B. napus and S. alba 2x or 4x incongruity barriers were observed on the stigma, in the style, and in the ovary resulting in a low frequency of ovules wit h micropylar penetration per siliqua. Open flower-pollination compared to bud-pollination generally was the more favourable procedure for po llen grain germination and pollen tube growth in crosses involving S. alba, but for micropylar penetration and seed set no differences were observed. Crosses between S. alba 2x (female) and B. napus (male) were found to result in a higher frequency of ovules with micropylar penet ration as compared to reciprocal crosses or crosses with S. alba 4x. A ll reciprocal crosses between R napus and S. alba 2x or 4x were unsucc essful when no embryo rescue was applied. Embryo rescue shortly after pollination, i.e. 2 to 5 days, however, resulted in hybrid seeds and p lants, but only when applied to crosses between S. alba 2x (female) an d B. napus (male). The possible effects of the genome constitution, ta xonomic distance and the parthenogenctic and parthenogenesis inducing ability of the parental genotypes on the observed malfunctions at the pre- and/or post-zygotic stage of the pollen grain-pistil interactions are discussed.