Cytogenetic Relationships between Paspalum pubiflorum and Three South American Paspalum Species

This study reports the meiotic chromosome pairing behavior and method of reproduction of three Paspalum pubiflorum accessions and their F1 hybrids with P. juergensii (2n=2x=20; JJ), P. intermedium (2n=2x=20; II), and two dallisgrass (P. dilatatum) biotypes (yellow‐anthered [2n=4x=40; IIJJ] and Uruguayan [2n=6x=60; IIJJXX]). The P. pubiflorum accessions were sexual hexaploids with 60 chromosomes that paired as 30 bivalents during meiosis. The yellow‐anthered dallisgrass × P. pubiflorum hybrids had 50 chromosomes, with a mean pairing behavior of 36.62 I\,+8.70 II, indicating that one P. pubiflorum genome is homologous with either the I or J genome in the yellow‐anthered biotype. The F1 hybrids between P. pubiflorum and P. juergensii and P. intermedium had 40 chromosomes. Mean chromosome pairing behavior for P. pubiflorum × P. juergensii hybrids was 24.05 I\,+7.97\,II\,+0.12 III, and 35.26 I\,+2.37 II for the P. pubiflorum × P. intermedium hybrids. Paspalum pubiflorum also was crossed with hexaploid Uruguayan dallisgrass, and the hybrid had 60 chromosomes with a mean pairing frequency of 40.52 I\,+9.74 II. These findings indicate that the common genome between P. pubiflorum and dallisgrass is the J genome. Based on chromosome pairing in the P.\,pubiflorum× P.\,intermedium hybrids, there is some residual homology between the I genome and another genome from P. pubiflorum. There appears to be very limited pairing between a few members of the X genome in the Uruguayan biotype and members of a third P. pubiflorum genome. In most hybrids, the sporogenous tissue in the ovules deteriorated, resulting in a high frequency of ovule abortion. However, aposporous embryo sacs were present in ovules of the P. pubiflorum × Uruguayan dallisgrass hybrid, indicating that the genes controlling apomixis were from the apomictic Uruguayan dallisgrass.