MEIOTIC ANOMALIES IN HYBRIDS BETWEEN WHEAT AND APOMICTIC ELYMUS-RECTISETUS (NEES IN LEHM) A LOVE AND CONNER

Four B-III hybrids (2n = 9x = 63, ABDStStYYWW) were obtained between w heat (Triticum aestivum L., 2n = 6x = 42, AABBDD) and a diplosporic an d 2n-pollen-producing Elymus rectisetus (2n = 6x = 42, StStYYWW) acces sion, We determined whether apomeiosis and 2n pollen formation, which occur in the male parent, also occur in the Fill hybrids. Pistils mere cleared for UV microscopy of callose and recleared for cytological ob servations using interference contrast microscopy. Callose fluorescenc e from most megaspore mother cells (MMCs) was typical of sexual specie s. These were classified as sexual. Abnormally elongated MMCs with wal ls devoid of callose were observed in 4.7% of pistils collected at mei otic prophase. These traits are typical of many apomeiotic MMCs in E. rectisetus. Asynapsis followed by mitosis in pollen mother cells (PMCs ) consistently preceded unreduced pollen formation in E. rectisetus. T his was not observed in the Fill hybrids, though the following meiotic anomalies were observed: (i) asynapsis, aggregation of chromosomes to several poles, and multiple divisions to form four to eight unbalance d microspores, and (ii) incomplete synapsis, formation of anaphase I l aggards, and a second division resulting in four unbalanced microspore s with micronuclei, The wheat haplome enforced PMC meiotic pairing (al beit abnormal) among homologous E. rectisetus chromosomes and generall y inhibited apomeiosis, also by enforcing meiosis. Diplospory may be c aused by the expression of embryo sac signals from one genome precocio usly expressed with megasporogenesis signals from another. If this is correct, the successful induction of apomixis in wheat may require the transfer of alien gene cassettes that confer appropriate degrees of r eproductive asynchrony.