Apomixis and sexuality in Themeda forssk. At different ploidy levels (gramineae)

✍ Scribed by S. P. Birari

• Publisher: Springer Netherlands
• Year: 1980
• Tongue: English
• Weight: 512 KB
• Volume: 54
• Category: Article
• ISSN: 0016-6707
• DOI: 10.1007/bf00055982

✦ Synopsis

The twenty-chromosome, diploid species Themeda anathera (Nees) Hack., T. tremula Nees ex Steud., T. strigosa (Ham) A. Camus, T. hookeri (Griseb.) A. Camus, T. mooneyi Bor and two forty-chromosome, tetraploid species, T. villosa (Nees) A. Camus and T. caudata (Nees) A. Camus with normal meiosis, are sexual. Two more tetraploids, T. quadrivalvis (L.) O. Ktze and T. triandra Forssk., one fifty-chromosome pentaploid, T. longispatha Raiz et Jain, two sixtychromosome hexaploids, T. dacruzii Birari and T. arundinacea (Roxb.) with moderate degrees of meiotic irregularities, are facultative apomicts. Eighty-, ninety-and one-hundred-and-ten-chromosome, octo-, nona-and 11 -ploids of T. triandra with severe meiotic irregularities are obligate apomicts. Sexual species produce reduced 8-nucleate bipolar Polygonum-type of embryosacs in the ovules. In the facultative apomicts, most of the ovules exhibit the simultaneous development of unreduced, 4-nucleate monopolar Panicum type and reduced, 8-nucleate Polygonum type embryosacs. In a few cases the sexual embryosacs degenerated and only Panicum type matured. In obligate apomicts there was early degeneration of MMC, dyads and, in few instances, mature sacs of the Polygonum type and only four-nucleate Panicum type embryosacs developed. The ovules in this group of cytotypes produced 1 to 5 embryosacs of the Panicum type.