Selection of maize hybrids for tolerance to aluminum in minimal solution.

The aim of this study was to determine the Al concentration and the period of exposure of the roots of maize hybrids in minimal solution for efficient selection of genotypes that are Al-tolerant. Two experiments were performed (48 and 96 h of exposure) with increasing doses of Al in minimal solution; the block design was completely randomized in a split-plot design with 3 replications. By assessing differences in root growth (cm) and the percentage of inhibition of the growth of the main root (%), a marked decrease was observed in maize root growth with increasing Al concentration in the solution. Exposure of the roots to 2 mg/L Al for 48 h in minimal solution was the most efficient for selecting sources of tolerance, particularly for the hybrids H 44 and H 38.

Genetic diversity in the germplasm of tropical maize landraces determined using molecular markers.

Maize landraces derived from tropical germplasm represent an important source of genetic variability, which is currently poorly understood and under-exploited by Brazilian crop breeding programs. The aims of our study were to a) estimate the genetic diversity across 48 varieties of maize landraces cultivated at different locations in the States of Rio Grande do Sul (RS) and Paraná (PR) by means of random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and amplified fragment length polymorphism (AFLP) markers; b) cluster these varieties based on their genetic similarity estimates, and c) establish possible correlations between genetic similarity and germplasm collection sites. Maize landrace accessions were genotyped through the 30 RAPD, 47 SSR, and 25 combinations of AFLP primers. The results revealed high levels of variability across landraces within and between collection sites. AFLP analysis resulted in amplification of 762 polymorphic fragments and a polymorphic index of 40.3%, followed by RAPD with 335 fragments (81.9%) and SSR with 105 fragments (78.3%). The genetic similarity estimates of the investigated landraces ranged from 41 (SSR) to 74% (AFLP), and the amplitudes of these indices were notably similar between RAPD and SSR, as well as between AFLP and joint analysis. Regarding the RAPD and AFLP dendrograms, groups comprising accessions from RS prevailed, whereas SSR comprised varieties from both collection sites. Groups exclusive to RS or PR support the hypothesis that divergence between groups is possible owing to the fixation of regional adaptation alleles and to spatial barriers hindering genetic flow between locations.

Population structure and genetic diversity analysis in Gynaikothrips uzeli (Zimerman, 1909) (Thysanoptera: Phlaeothripidae) by RAPD markers.

Thrips are small insects (0.5-3.0 mm) with distinct habits and life histories characterized by haplodiploid sex determination. In general, low levels of genetic diversity have been reported in haplodiploid insects, although most reports focus on the order Hymenoptera. Therefore, we used RAPD markers to evaluate the structure and both inter- and intra-population genetic variability of Gynaikothrips uzeli (Thysanoptera: Phlaeothripidae). Six populations, three from Paraná state, southern Brazil, and three from Bahia, northeastern Brazil, were studied. Similarly to other haplodiploid insects, the genetic diversity of G. uzeli was reduced. This result is putatively related to the haplodiploid sex determination system, which yields little genetic variation, and to ecological traits of the studied species, such as the low dispersal abilities and life mode in leaf galls. All individuals were homogeneously clustered in their respective collection sites, forming two main groups in which populations from similar environments were more closely related. The analyzed populations were highly structured, and the genetic variation was higher among than within populations.