Cytogenetic relationships between Paspalum pubiflorum and three South American Paspalum species

This study reports the meiotic chromosome pairing behavior and method of re production of three Paspalum pubiflorum accessions and their F-1 hybrids wi th P. juergensii (2n=2x=20; JJ), P. intermedium (2n=2x=20; II), and two dal lisgrass (P. dilatatum) biotypes (yellow-anthered [2n=4x=40; IIJJ] and Urug uayan [2n=6x=60; IIJJXX]). The P. pubiflorum accessions were sexual hexaplo ids with 60 chromosomes that paired as 30 bivalents during meiosis. The yel low-anthered dallisgrass x P. pubiflorum hybrids had 50 chromosomes, with a mean pairing behavior of 36.62 I + 8.70 II, indicating that one P. pubiflo rum genome is homologous with either the I or J genome in the yellow-anther ed biotype. The F-1 hybrids between P. pubiflorum and P. juergensii and P. intermedium had 40 chromosomes. Mean chromosome pairing behavior for P. pub iflorum x P. juergensii hybrids was 24.05 I + 7.97 II + 0.12 III, and 35.26 I + 2.37 II for the P, pubiflorum x P, intermedium hybrids. Paspalum pubif lorum 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. The se findings indicate that the common genome between P. pubiflorum and dalli sgrass is the J genome. Based on chromosome pairing in the P. pubiflorum x I! intermedium hybrids, there is some residual homology between the I genom e and another genome from P. pubiflorum. There appears to be very limited p airing between a few members of the X genome in the Uruguayan biotype and m embers of a third P. pubiflorum genome. In most hybrids, the sporogenous ti ssue in the ovules deteriorated, resulting in a high frequency of ovule abo rtion. However, aposporous embryo sacs were present in ovules of the P. pub iflorum x Uruguayan dallisgrass hybrid, indicating that the genes controlli ng apomixis were from the apomictic Uruguayan dallisgrass.