ABSTRACT
Summary Several grass species related to Panicum milioides Nees ex Trin., a species with intermediate photosynthetic characteristics, were collected in South America. Panicum prionitis Griseb. was found to possess C4 photosynthesis. Panicum schenckii Hack, and Panicum decipiens Nees ex Trin. were found to have intermediate photosynthesis, like P. milioides. Panicum laxum Sw., Panicum hylaeicum Mez., and Panicum rivulare Trin. were found to have C3 photosynthesis. In this study, we describe the cytogenetic and reproductive characteristics of these species for future studies of hybridization among distinct photosynthetic types. A basic chromosome number of 10 was common for all species. Diploid (2n = 2 x = 20), tetraploid (2n = 4 x = 40), and hexaploid (2n = 6 x = 60) accessions were found. P. prionitis possessed a diploid and tetraploid accession. P. miliodes was diploid, P. schenckii was hexaploid, and P. decipiens exhibited one diploid and one hexaploid accession. P. laxum, P. hylaeicum, and P. rivulare were all tetraploid. There was stable and primarily bivalent pairing at metaphase I in all species, which resulted in a high percentage of stainable pollen. Embryo sac analyses showed normal sexual development in all plants except one accession of P. prionitis, which was found to possess multiple embryo sacs at anthesis. Selfpollinated seed set was high in all species. An intraspecific hybrid resulted from a cross of two P. laxum accessions. Although this hybrid possesses more multivalent pairing than either of its parents did, it did produce large amounts of viable pollen and seed. Similar and stable cytogenetic characteristics and similar taxonomy indicate possible success in producing hybrids among these species for a genetic study of photosynthetic characteristics in grasses.
