CYTOLOGICAL MECHANISMS OF 2N EGG FORMATION IN A DIPLOID GENOTYPE OF MEDICAGO-SATIVA SUBSP FALCATA

Gametes formed without meiosis in alfalfa would be useful in basic and applied research. Therefore, the cytological analysis of macrosporoge nesis of a diploid plant of Medicago sativa subsp. falcata (L.) Arcang eli (named PG-F9), previously selected as a good 2n egg producer, was conducted. A stain-clearing technique was applied which also allowed t he analysis of microsporogenesis to be performed. Two mechanisms of 2n egg formation were determined: absence of the second meiotic division (mechanism of the SDR type) and apomeiosis. In particular, it is note worthy that 2n eggs produced via apomeiosis should retain the same par ental genotype, because apomeiotic cells give rise directly to the fem ale gametophyte without undergoing meiosis. The presence of binucleate female gametophytes in the ovules at an early stage of development co nfirmed the presence of apomeiosis in PG-F9. These abnormalities conce rned only macrosporogenesis; in fact, the analysis of microsporogenesi s showed the production of normal tetrads of microspores after normal meiosis. Possible application of the discovered mechanisms of 2n egg p roduction in breeding research are discussed.