Orlando Toro

A new variant of arcelin in wild common bean, Phaseolus vulgaris L., from southern Mexico

Arcelin, a seed protein discovered in wild Phaseolus vulgaris L. accessions, gives high levels of resistance to the Mexican bean weevil [MBW; Zabrotes subfasciatus (Boheman)]. Six variants of arcelin have been described. In this paper we report on a new variant, arcelin 7, found in six wild bean accessions collected in the southern state of Chiapas in Mexico. The new variant is clearly distinct from previously reported ones. It confers high levels of resistance to MBW, comparable to those due to the presence of arcelin 1, arcelin 2 and arcelin 4. Accessions containing arcelin 7 were not as resistant as the one containing arcelin 5 but significantly better in terms of resistance than arcelins 3 and 6. Arcelin 7 was found in a poorly sampled area of Mexico threatened with genetic erosion due to expanding agricultural operations. This exemplifies the need for urgent additional collecting efforts.

Multiple origins of the determinate growth habit in domesticated common bean (Phaseolus vulgaris)

BACKGROUND AND AIMS The actual number of domestications of a crop is one of the key questions in domestication studies. Answers to this question have generally been based on relationships between wild progenitors and domesticated descendants determined with anonymous molecular markers. In this study, this question was investigated by determining the number of instances a domestication phenotype had been selected in a crop species. One of the traits that appeared during domestication of common bean (Phaseolus vulgaris) is determinacy, in which stems end with a terminal inflorescence. It has been shown earlier that a homologue of the arabidopsis TFL1 gene - PvTFL1y - controls determinacy in a naturally occurring variation of common bean. METHODS Sequence variation was analysed for PvTFL1y in a sample of 46 wild and domesticated accessions that included determinate and indeterminate accessions. KEY RESULTS Indeterminate types - wild and domesticated - showed only synonymous nucleotide substitutions. Determinate types - observed only among domesticated accessions - showed, in addition to synonymous substitutions, non-synonymous substitutions, indels, a putative intron-splicing failure, a retrotransposon insertion and a deletion of the entire locus. The retrotransposon insertion was observed in 70 % of determinate cultivars, in the Americas and elsewhere. Other determinate mutants had a more restricted distribution in the Americas only, either in the Andean or in the Mesoamerican gene pool of common bean. CONCLUSIONS Although each of the determinacy haplotypes probably does not represent distinct domestication events, they are consistent with the multiple (seven) domestication pattern in the genus Phaseolus. The predominance of determinacy in the Andean gene pool may reflect domestication of common bean prior to maize introduction in the Andes.

Variability in Andean nuña common beans (Phaseolus vulgaris, Fabaceae)

Nuñas are a group of common bean (Phaseolus vulgaris, Fabaceae) varieties, whose grains are consumed after toasting in their original Andean habitats. Nowadays, these varieties are restricted to certain parts of the highlands of Peru and Bolivia. Linguistic, ethnobotanical, and archaeological data suggest that they were grown in that zone duringpre-Hispanic times. SDS-PAGE electrophoresis shows a wide range ofphaseolin types amongnuñas, many of which are present in sympatric wild forms. This paper discusses the possibility thatnuñas resulted from an early and widely applied selection pressure during bean domestication in the Andes.RésuméLas nuñas o ‘frijoles reventones’ son un grupo de variedades de frijol común de las cuales los granos se consumen tostados en su hábitat original en los Andes. Este hábitat se restringe en la actualidad a algunas paries altas del Perú y de Bolivia. Los datos linguísticos, etnobotánicos y arqueológicos dejan suponer una presencia pre-Hispánica en la zona. Los análisis electroforéticos en SDSPAGE muestran una amplia gama de tipos de faseolina, varios de estos presentes enformas silvestres simpátricas. Se discute la posibilidad que las nuñas corresponden a una presión selectiva aplicada en forma temprana y amplia en el proceso de domesticatión del frijol en los Andes.

Tracing the origin of Spanish common bean cultivars using biochemical and molecular markers

Fifty-four accessions of Phaseolus vulgaris cultivated in Spain and representing a broad variability for this country, were studied together with 30 samples of wild forms of American origin. Two reference cultivars (from the Andes and Mesoamerica) plus two outgroups (P. coccineus and Vigna unguiculata) were also included. RAPD analysis of DNA leaf extracts were carried out with four selected primers. We also studied morphological characters of the seeds and the phaseolin electrophoretic patterns. Multivariate analysis with the UPGMA method using RAPD data clustered the samples in four groups and, comparing with morphological data and phaseolin types, showed that the Spanish cultivars were mainly of Andean origin. Nevertheless, occurrence of introgression in Spain and the consideration of the country as a second center of variability for beans can also explain the obtained results.