A core AFLP map of aposporic tetraploid Paspalum notatum (Bahiagrass).

ORTIZ, JUAN PABLO AMELIO; STEIN, J.; MARTINEZ, ERIC JAVIER; QUARIN, CAMILO LUIS; SILVINA CLAUDIA PESSINO

Aberystwyth, UK

Congreso; 4th International Symposium on the Molecular Breeding of Forage and Turf, Aberystwyth, Wales, UK; 2005

IGER (Institute of Grassland and Environmental Research) BBSRC

Introduction: Paspalum notatum (Bahiagrass) is a perennial rhizomatous species that reproduces by aposporous apomixis. Tetraploid races (2n=4x=40) are widely distributed from Central to South America and constitute one of the most valuable natural forage grass for the subtropical areas of Paraguay, south of Brazil and north-eastern Argentina. Polysomic inheritance and multivant chromosome pairing proved autoploid origin for the tetraploid races of bahiagrass. Apospory in the species is controlled by a single locus with distorted segregation ratio. The objectives of this work were to develop of a core genetic linkage map of the species by using AFLP markers and characterize the genomic region related to apospory. Materials and methods: A mapping population of 113 individuals was generated by crossing a tetraploid sexual plant (Q4188) with an aposporous individual from accession Q4117. Progenies were classified for their mode of reproduction (asposporous vs. non-aposporous) by molecular and cytoembriological analyses according to Martínez et al. 2003. AFLP markers were generated employing EcoRI and MseI and primers with 1 and 3 selective bases (Stein et al. 2004). A c2 test was used to determine the goodness of fit between the observed and expected genotypes for each class of segregation ratio. Data from each parental genotype were analyzed independently using the mapping program JoinMap1.4 with LOD values between 3.0 and 5.0. Linkage groups were constructed considering only single dose alleles (SDA) segregating from the male parent (asposporic).Map units in cM were derived from the Kosambi mapping function. Results: As a result of using a tetraploid F1 population derived from non-inbred parents, different allelic configuration per locus were observed (Table 1). Classification of F1 plants for their mode of reproduction showed 98 nonaposporous and 15 aposporous individuals. Table1: Segregation of AFLP markers in the mapping population Type of Number of markers in each class of segregation ratio marker 1:1a 3:1b 5:1b 3:1/5:1b 11:1c DistortedTotal Paternal 166 23 14 24 - 33 260 Maternal 245 20 11 20 - 16 308 Both - 60c - - 38 5 103 a single dose alleles (SDAF), bdouble dose alleles, callelic bridges, d at p< 0.01 The total genetic map distance covered was about 1,430 cM, with an average of approximately 10 cM between markers. The linkage group carrying the locus for apospory (apo-locus) was defined by 28 loci on 32 cM. Twelve markers resulted completely linked to the apo-locus, while the rest showed recombination values between 0.6 and 18 cM, at both sides of it. The complete co-segregation of several markers and apospory confirmed the suppression of recombination in this genomic region reported by Martínez et al. (2003). The average distance between markers in the apo-group was about 1 cM. Conclusions: A core genetic linkage map of aposporous tetraploid P. notatum was built with AFLP markers. It can be employed for fundamental research as well as for localising genes of agronomic interest. The structure of the linkage group carrying apospory suggests that it could be a large chromosome segment containing several genes. A detailed molecular analysis of this segment, based on the utilisation of the molecular markers linked to apospory already available, could allow the identification of the factor/s responsible for the trait in the species. References: Martínez, E.J., E. Hopp, J. Stein, J.P.A. Ortiz and C.L. Quarin (2003). Genetic characterisation of apospory in tetraploid Paspalum notatum based on the identification of linked molecular markers. Mol. Breed. 12 (4): 319- 327. Stein, J., C.L. Quarin, E.J. Martínez, S.C. Pessino and J.P.A. Ortiz (2004). Tetraploid races of Paspalum notatum showed polysomic inheritance and preferential chromosome paring around the apospory-controlling locus. Theor. Appl. Genet. 109:186 –191.