Submitted to: International Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/1997
Publication Date: N/A
Interpretive Summary: A number of plant introductions of the grass ribbed paspalum were recently introduced into the US from Argentina and Bolivia. This grass has several desirable characteristics including resistance to the disease ergot which is a major problem in several important forage grasses including common dallisgrass. Since common dallisgrass and ribbed paspalum are related, it may be possible to transfer the genes for resistance from ribbed paspalum to common dallisgrass by crossing the two grasses. However, nothing is known about the chromosome number, cytological behavior, and method of reproduction of this new germplasm and this fundamental information is needed before crosses are attempted. All of the ribbed paspalum introductions had 40 chromosomes and they reproduced by both sexual and asexual means. Crosses were attempted between ribbed paspalum and yellow anthered dallisgrass and another paspalum species and some hybrids were recovered. The hybrids were not infected by ergot but they produced very little seed. The cytology and reproductive behavior of the hybrids were investigated and it was determined that ribbed paspalum and dallisgrass are not closely related. This is the reason for the extremely low seed set in the hybrids and indicates that crossing ribbed paspalum and dallisgrass is not a feasible approach of transferring the genes for ergot resistance to dallisgrass.
Technical Abstract: This study describes the meiotic chromosome pairing behavior and method of reproduction of Paspalum malacophyllum accessions and their F1 hybrids with diploid P. juergensii (2n=2x=20) and tetraploid P. dilatatum (2n=4x=40). All P. malacophyllum accessions were tetraploids with 40 chromosomes. Their mean meiotic chromosome pairing behavior was 0.82 I + 13.40 II + 0.02 2III + 1.58 IV. As many as seven quadrivalents were observed indicating th species is an autotetraploid. An examination of magasporogenesis and the subsequent female gametophyte development revealed that all accessions were facultative apomicts with the form of apomixis being apospory. This clarifies the uncertainty regarding the reproductive behavior of this species. All P. juergensii x P. malacophyllum hybrids were triploids with 30 chromosomes which associated primarily as 10 I + 10 II. The P. dilatatum x P. malacophyllum hybrids had 40 chromosomes which associated essentially as 20 I + 10 II. The ten bivalents in both groups of hybrids represent autosyndetic pairing of the P. malacophyllum chromosomes, thus supporting the autoploid nature of this species. The ten univalents in the P. juergensii x P. malacophyllum hybrids are members of the J genome from P. juergensii which has the genome formula JJ, and the 20 univalents in the P. malacophyllum x P. dilatatum hybrids are members of the I and J genomes from P. dilatatum which has the genome constitution IIJJ. Because P. malacophyllum does not possess the I or J genomes and its chromosomes pair autosyndetically, it was assigned the genome formula MMMM. Cytologically, both groups of F1 hybrids reproduced as facultative aposporous apomicts.