Characterisation of genetic diversity in maize landraces of Uruguay and Brazil

Maize landraces are highly dynamic populations and at the same time a tool for conserving genetic resources and generating diversity. Information on maize diversity in Uruguay and Brazil was updated in a new reclassification of South American lowland landraces, however, this study did not address the area of cytogenetics. Chromosomal knobs are blocks of heterochromatin that stain differentially and have been used to cytogenetically characterise different maize genotypes. The aim of this work was to characterise the genetic variability of maize landraces from Uruguay and Brazil using cytogenetic techniques, based on the study of the number and size of knobs, percentage of heterochromatin and presence of supernumerary B chromosomes (Bs). Thirty-six accessions of maize landraces classified into 21 races were studied. The analysis of number of knobs and presence of Bs were performed on mitotic metaphase chromosomes by DAPI fluorescence banding. Significant variation was observed in the number of knobs for dent and floury maize, and great variability in the percentage of heterochromatin, in addition medium to large knobs were found in all the individuals analysed. The races also showed great variability in terms of number of knobs and heterochromatin percentage, although not significant. In the results obtained, the difference in the frequency of Bs stands out, 0.25 for Uruguay and 0.025 for Brazil, being the first record made for a group of maize landraces for both countries. In conclusion, there is intragenomic variability in the number of knobs and percentage of heterochromatin. Moreover, there are significant differences in Bs frequencies between both countries, which may be associated with the route of maize dispersal to the lowlands.