MECHANISMS OF APOMIXIS IN ELYMUS RECTISETUS FROM EASTERN AUSTRALIA AND NEW ZEALAND

Abstract

Megasporogenesis was examined in cleared ovaries of 23 accessions of hexaploid Elymus from southeastern Queensland, northeastern New South Wales, the Australian Capital Territory, and the South Island of New Zealand. Apomixis was confined to the 17 accessions that morphologically corresponded to E. rectisetus (Nees in Lehm.) Löve et Connor. Female meiotic development followed the Polygonum type. Apomeiotic development was delayed relative to meiotic development because of a lengthy period of MMC vacuolation and nuclear stretching that occurred in place of meiosis I. Amitosis was evident in up to possibly five percent of the MMC's during nuclear stretching. A subsequent mitotic division facultatively functioned as meiosis II or the first embryo‐sac mitosis to yield a 2n megaspore dyad, a hemidyad with an incomplete crosswall, or a directly binucleate embryo sac. Nuclear stretching generally resumed in the chalazal daughter nucleus from the apomeiotic division, but was not seen later in embryo sac development. When a dyad formed, its chalazal member would enlarge and develop into the embryo sac. The organized embryo sac was of the conventional eight‐nucleate, seven‐celled structure prior to antipodal proliferation, regardless of meiotic or apomeiotic origin. Microsporocyte meiosis was normal in both sexuals and apomicts. Deposition of a slightly birefringent substance, possibly callose, was deficient around megasporocytes, megaspores, and microsporocytes in the apomicts.