Species relations among wild Arachis species with the A genome as revealed by FISH mapping of rDNA loci and heterochromatin detection |
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Authors: | G Robledo G I Lavia G Seijo |
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Institution: | (1) Instituto de Botánica del Nordeste, Sargento Cabral 2131, 3400 Corrientes, Argentina;(2) Facultad de Ciencias Exactas, Naturales y Agrimensura (UNNE), Corrientes, Argentina |
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Abstract: | Section Arachis of the homonymous genus includes 29 wild diploid species and two allotetraploids (A. monticola and the domesticated peanut, A. hypogaea L.). Although, three different genomes (A, B and D) have been proposed for diploid species with x = 10, they are still not well characterized. Moreover, neither the relationships among species within each genome group nor
between diploids and tetraploids (AABB) are completely resolved. To tackle these issues, particularly within the A genome,
in this study the rRNA genes (5S and 18S–26S) and heterochromatic bands were physically mapped using fluorescent in situ hybridization
(FISH) in 13 species of Arachis. These molecular cytogenetic landmarks have allowed individual identification of a set of chromosomes and were used to construct
detailed FISH-based karyotypes for each species. The bulk of the chromosome markers mapped revealed that, although the A genome
species have a common karyotype structure, the species can be arranged in three groups (La Plata River Basin, Chiquitano,
and Pantanal) on the basis of the variability observed in the heterochromatin and 18S–26S rRNA loci. Notably, these groups
are consistent with the geographical co-distribution of the species. This coincidence is discussed on the basis of the particular
reproductive traits of the species such as autogamy and geocarpy. Combined with geographic distribution of the taxa, the cytogenetic
data provide evidence that A. duranensis is the most probable A genome ancestor of tetraploid species. It is expected that the groups of diploid species established,
and their relation with the cultigen, may aid to rationally select wild species with agronomic traits desirable for peanut
breeding programs. |
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