CYTOGENETICS OF PASPALUM CONSPERSUM AND ITS GENOMIC RELATIONSHIP WITH YELLOW-ANTHERED P. DILATATUM AND P. MALACOPHYLLUM

Abstract

Paspalum conspersum Schrad. ex Schult. is a leafy, robust, warm season perennial bunchgrass native to South America. A cytogenetic investigation was conducted to determine the feasibility of using the grass in an interspecific hybridization program. Four introductions were studied and each had a chromosome number of 2n = 4x = 40. During meiosis, the chromosomes paired primarily as bivalents with an occasional quadrivalent and a limited number of univalents. A study of megasporogenesis and embryo sac development revealed that the plants were sexual. Eighty hybrids were obtained from yellow-anthered P. dilatatum Poir, 2n = 4x = 40, × P. conspersum. Thirty of these were examined cytologically. All had a chromosome number of 2n = 4x = 40. Mean meiotic pairing was 19.87 I, 9.94 II, 0.12 III, and 0.004 IV. Because of segmental homology between the P. conspersum genomes, it was difficult to determine the relationship between the two species. Thus, P. conspersum was crossed with autotetraploid P. malacophyllum Trin., 2n = 4x = 40, to determine the amount of autosyndetic pairing between the P. conspersum chromosomes. One hybrid was obtained and it had a chromosome number of 2n = 4x = 40. The mean pairing behavior was 15.74 I, 12.07 II, and 0.008 IV. Ten of the bivalents were interpreted as autosyndetic pairing of the P. malacophyllum chromosomes and the remaining 2.07 bivalents as autosyndetic pairing of the P. conspersum chromosomes. These findings also show no homology between P. conspersum and P. malacophyllum chromosomes and suggest the species are not closely related. Since there is limited autosyndetic pairing between members of the P. conspersum genomes, data from the P. dilatatum × P. conspersum hybrids indicate the two species have at least one common genome. Megasporogenesis was normal in both groups of hybrids. However, in the P. dilatatum × P. conspersum hybrids, the sexual tissue generally deteriorated, resulting in complete abortion of the female gametophyte. In the P. conspersum × P. malacophyllum hybrid, about 90% of the mature ovules had sexual embryo sacs. However, in the remaining ovules there was either deterioration of the sexual tissue or other abnormalities.