S. N. Parentoni

Heterotic groups based on yield-specific combining ability data and phylogenetic relationship determined by RAPD markers for 28 tropical maize open pollinated varieties

Twenty eight maize open pollinated varieties (OPVs) were crossed in a diallel scheme and the 378 F1s were evaluated in 10 environments in Brazil. Based on yield-specific combining ability data (SCA), these varieties were classified in four heterotic groups. The consistence of the proposed heterotic groups was confirmed comparing intra- and inter-group F1 values and midparent heterosis. Superior OPVs combinations for use as a source of inbreds in hybrid breeding programs were determined. RAPD markers were used to genotype these varieties. A UPGMA dendogram, based on marker data from 50 primers and 178 polymorphic bands, was obtained. Phylogeny obtained with RAPD markers agreed with known pedigree data. Dent germplasm tended to group separately from flint germplasm. Multidimensional Scaling Analysis on marker data and morphological data showed a higher degree of genetic divergence among the dent germplasm than among the flint germplasm used in this study. Correlation between RAPD marker estimated genetic distance and SCA for yield was low and positive (r = 0.16**).

Mechanisms of phosphorus efficiency in maize

The National Maize and Sorghum Research Center of the Brazilian Agricultural Research Corporation, has been working for the past two decades to increase plant adaptation to low P levels in acid soils. We have studied several mechanisms in order to clarify the differences between genotypes in relation to phosphorus efficiency using maize standards for phosphorus efficiency developed at Embrapa Maize and Sorghum.

Potencial genético de um sintético de milho de grãos duros para formação de híbridos

The objective of this study was to determine the genetic potential of a semi-early maize synthetic with flint type kernel (Sin EEL Flint). The estimation of genetic parameters was obtained with S2 progenies, and the performance of the progenies in hybrid combinations were evaluated. One hundred fourty-two S2 progenies of Sin EEL Flint were used. They were obtained by top crossings with a contrasting heterotic synthetic of dent type kernel. These topcross progenies were tested in a lattice design 12 x 12 with two replications in two locations, Sete Lagoas and Londrina. The selected topcross no 101, with specific adaptation for Londrina. and no72, being adapted to both locations, were the best yieldings (PED) with 12069Kg ha-1 and 11068Kg ha-1, respectively. Values of the estimated parameters for , CVg and h2 were similar to those found in other studies conducted in tropical conditions. It was observed that this synthetic has enough genetic and potential variability to inbred line extraction for hybrid production and to be used as germoplasm source in breeding programs.