A sexual highly diploidized autotetraploid plant induced from the diploid cytotype of Paspalum chaseanum Parodi

Abstract

Paspalum is one of the most common native grass genera of the New World grasslands, and it includes many wild natural forage species and rare domesticated ones. Polyploidy is widespread among the genus. Many species are multiploid, which basically involve two components: a sexual self-incompatible diploid cytotype and a conspecific apomictic tetraploid, pseudogamous, and self-compatible cytotype, though other apomictic polyploid levels may occur in the same species. Tetraploid individuals, reproducing exclusively sexually, have never been identified in a natural apomictic tetraploid Paspalum species. Doubling the chromosome number of a 2x cytotype is used to obtain a sexual autotetraploid to carry out sexual × apomictic crosses in breeding programs for plant improvement. After numerous attempts we generated only one autotetraploid plant of P. chaseanum (I4C) which reproduced sexually and was highly self-incompatible. An unexpected preferential chromosome pairing resulted in the cytological diploidization of I4C. Despite each chromosome having three copies in I4C, meiotic chromosome configurations showed just 9.9% chromosomes forming multivalents (trivalents and quadrivalents), 82.1% bivalents, plus 7.9% univalents. The possible causes of this preferential pairing were analyzed. Although highly self-incompatible, it was fertile in crosses following intra- and interspecific pollinations, but with variable seed set, from over 45% when crossed with an apomictic natural tetraploid strain of P. chaseanum, to 0.9% with a strain of P. wrightii. Thus, a novel autotetraploid P. chaseanum was synthesized with very interesting characteristics: sexual reproduction, high self-incompatibility, variable cross-compatibility, and high cytological diploidization. All valuable attributes for breeding programs in a forage grass.