Origin of triploid Arachis pintoi Krapov. & W.C. Gregory (Leguminosae) by autopolyploidy evidenced by FISH and meiotic behavior

GRACIELA LAVIA, ALEJANDRA ORTIZ, GERMÁN ROBLEDO, AVELIANO FERNÁNDEZ AND GUILLERMO SEIJO

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2011 vol. 108 p. 103 - 111

0305-7364

? Background and Aims Polyploidy is a dominant feature of flowering-plant genomes, including those of manyimportant crop species. Arachis is a largely diploid genus with just four polyploid species. Two of them are economicallyimportant: the cultivated peanut and A. glabrata, a tropical forage crop. Even though it is usuallyaccepted that polyploids within papilionoid legumes have arisen via hybridization and further chromosome doubling,it has been recently suggested that peanut arose through bilateral sexual polyploidization. In this paper, thepolyploid nature of the recent, spontaneously originated triploid cytotype of the tropical lucerne, A. pintoi, wasanalysed, and thereby the mechanism by which polyploids may arise in the genus.? Methods Chromosome morphology of 2x and 3x A. pintoi was determined by the Feulgen´s technique and therDNA sites were mapped by FISH. To investigate whether polyploidization occurred by means of unreducedgametes, a detailed analysis of the microsporogenesis and pollen grains was made.? Key Results The 2x and 3x plants presented 9m + 1sm and a satellited chromosome type 2 in each haploidgenome. Physical mapping revealed a cluster of 18S?26S rDNA, proximally located on chromosome 6, andtwo 5S rDNA loci on chromosomes 3 and 5. Diploid plants presented 10II in meiosis while trivalents wereobserved in all triploids, with a maximum of 10III by cell. Diploid A. pintoi produced normal tetrads, butalso triads, dyads and monads. Two types of pollen grains were detected: (1) normal-sized with a prolateshape and (2) large ones with a tetrahedral morphology.?Conclusions Karyotype and meiotic analysis demonstrate that the 3x clone of A. pintoi arose by autopolyploidy.The occurrence of unreduced gametes strongly supports unilateral sexual polyploidization as the most probablemechanism that could have led to the origin of the triploid cytotype. This mechanism of polyploidization wouldprobably be one of the most important mechanisms involved in the origin of economically important species ofArachis, either by triploid bridge or bilateral sexual polyploidization.