Evolução cromossômica no complexo poliploide Lippia alba (Mill.) N. E. Br.

Abstract

The polyploidy is considered one of the most important factors in plant speciation, Lippia alba is an important medicinal herb being popularly used mainly in the treatment of gastric and respiratory problems. Once your popular use is employed as palliative for various human diseases. The species, of widely distribution possess extensive morphological plasticity and different chemotypes in addition to great karyotype variation. The present study aimed to characterize by means of cytogenetic techniques different cytotypes collected in natural environment and help to understand the dynamic of possible polyploid complex formation of the in L. alba. By means of chromosome banding and fluorescence in situ hibridization techniques in addition to meiotic and pollen viability analyses accomplished in five cytotypes of polyploid complex, it was possible to observe numerical and structural variations. The results suggest that intraspecific crosses autopolyploidization events caused the wide karyological variation in L. alba. The FISH technique, specially the rDNA 5S region, revealed important indications of autopolyploidy, once the number of marks of monoploid complement remained constant regardless of chromosome number. Moreover, the high rates of meiotic irregularities observed in triploid, aneuploid, tetraploid and hexaploid accessions also indicates abnormal paring and chromosomal segregation , a typical phenomenon of newly formed polypoids. In addition, the results of pollen viability by means of FDA test corroborate the meiotic data and support the hypothesis of of a polyploid complex formation in L. alba.