QUANTITATIVE-ANALYSIS OF APOSPOROUS PARTHENOGENESIS IN POA-PRATENSIS GENOTYPES

Several embryological and cytological techniques were developed to det ermine the degree of aposporous parthenogenesis vs. sexuality in diffe rent genotypes of the facultative apomictic grass Poa pratensis L. Fix ed embryo sacs were mechanically isolated and individually examined wi th phase-contrast and interference-contrast light microscopes. The deg ree of apospory was calculated as the ratio of embryo sacs with an emb ryo but without endosperm and the total number of embryo sacs studied per plant. The degree of apospory varied between 9 and 76% in nine pla nts. Photocytometry and flow cytometry were used to determine ploidy l evels in embryo and endosperm of individual embryo sacs in order to de termine their origin, asposporous vs. sexual. Results based on the cal culated degree of apospory agreed with the degree of apomixis deduced from homogeneity scores in field progeny tests. Callose deposition on the megaspore mother cell during megasporogenesis was studied in the s ame set of genotypes and the percentage of abnormal, micropylar callos e deposition closely agreed with results both of the embryo sac analys is and the progeny tests. Combined use of these techniques yields quan titative data on the aposporous tendency of individual genotypes of Po a pratensis.