Ploidy manipulation in guinea grass (Panicum maximum Jacq., Poaceae) utilizing a Hybridization-supplemented Apomixis-components Partitioning Approach (HAPA).

Ploidy manipulations are achieved by utilizing unreduced gametes, somatic chromosome doubling or haploidization. Apomixis, the asexual mode of reproduction through seeds, involves two of these phenomena viz., apomeiosis (unreduced embryo-sac formation) and parthenogenesis (fertilization-independent embryogenesis). The two components when partitioned may yield high frequencies of triploids and haploids, and thus, serve as a tool to manipulate ploidy levels when appropriately supplemented with hybridization schemes. Utilizing this Hybridization-supplemented Apomixis-components Partitioning Approach (HAPA), the largest ploidy series in a crop plant was generated in guinea grass (Panicum maximum Jacq.). Eighty-nine diverse guinea grass accessions were characterized for their reproductive capacities to identify tetraploid (2n = 4x = 32) accession(s) with high apospory but reduced parthenogenetic capacity, thereby producing a high frequency of hexaploid seeds. Seeds from accession IG 04-164 were utilized to produce a ploidy series by appropriately combining partitioned apomixis components and hybridizations in two seasonal cycles. We successfully obtained plants representing ploidies 3x, 4x, 5x, 6x, 8x and 9x, all derived from a single 4x progenitor. Production methodology, reproducibility and utilization of HAPA in cytogenetic and molecular studies are discussed.