Maurício Antônio Lopes

Mapping QTLs for aluminum tolerance in maize

Aluminum toxicity is one of the major constraints for plant development in acid soils, limiting food production in many countries. Cultivars genetically adapted to acid soils may offer an environmental compatible solution, providing a sustainable agriculture system. The aim of this work was to identify genomic regions associated with Al tolerance in maize, and to quantify the genetic effects on the phenotypic variation. A population of 168F3:4 families derived from a cross between two contrasting maize inbred lines for Al tolerance was evaluated using the NSRL and RSRL parameters in nutrient solution containing toxic level of aluminum. Variance analyses indicated that the NSRL was the most reliable phenotypicindex to measure Al tolerance in the population, being used for further QTL mapping analysis. RFLP and SSR markers were selected for bulked segregant analysis, and additional SSR markers, flanking the polymorphisms of interest, were chosen in order to saturate the putative target regions. Seven linkage groups were constructed using 17 RFLP and 34 SSR markers. Five QTLs were mapped on chromosomes 2, 6 and 8, explaining 60% of the phenotypic variation. QTL4 and marker umc043 were located on chromosomes 8and 5, close to genes encoding for enzymes involved in the organic acids synthesis pathways, a widely proposed mechanism for Al tolerance in plants. QTL2 was mapped in the same region as Alm2,also associated with Al tolerance in maize. In addition, dominant and additive effects were important in the control of this trait in maize.

Hematoxylin staining as a phenotypic index for aluminum tolerance selection in tropical maize (Zea mays L.)

Abstract Hematoxylin staining is an early indicator of Aluminum (Al) toxicity effects on the apices of young, developing roots grown in nutrient solution. In this work, the potential of this technique as a reliable and reproducible phenotypic index for Al tolerance in tropical maize genotypes was assessed, with its performance systematically compared to two other parameters widely used in breeding programs – relative seminal-root length (RSRL) and net seminal-root length (NSRL). Seeding roots from contrasting genotypes for Al sensitivity stained remarkably different after 24- and 48-h and 7-day exposures to 222 μM Al in nutrient solution, with the Al-dye complex being detected in both the outer (epidermis) and inner (cortex) portions of the roots from the sensitive cultivar. Hematoxylin staining was compared to the RSRL and NSRL parameters using 20 families from the third generation of selfing (S3) following the cross between two contrasting inbred lines that had been previously classified by the RSRL index in an independent procedure. The coloration technique showed the highest capacity to discriminate among tolerant and sensitive genotypes and displayed significant correlation coefficients to the other two indexes. Evaluation of the results from diallel crosses involving nine inbred lines proved that hematoxylin staining was also particularly adequate for identifying expressive hybrid vigor, as demonstrated by the general (GCA) and specific (SCA) combining ability estimates obtained by using the three indexes simultaneously. Hence, hematoxylin staining of Al-stressed root apices appears to be a powerful tool to assist in Al-tolerance selection in tropical maize breeding programs.

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**).

Identification of free fatty acids in maize protein bodies and purified α zeins by 13C and 1H nuclear magnetic resonance

Zeins, the maize storage proteins, are the most abundant proteins in the corn endosperm, and are synthesized on the rough endoplasmatic reticulum and deposited in discrete organelles called protein bodies. Several authors, using circular dichroism and optical rotatory dispersion, have concluded that these proteins have a high alpha-helical content in alcoholic solution. In this work we have studied these proteins, within the protein bodies themselves and after extraction from the corn grains with 70% ethanol, using NMR (nuclear magnetic resonance) spectroscopy. We conclusively demonstrate the presence of free fatty acids within both the protein bodies and also in the alcohol extracted alpha zeins. We present evidence for a direct interaction between the free fatty acids and the alpha zein proteins within the protein body and suggest possible mechanisms by which such an association has arisen during the evolution of the maize endosperm.

Embrapa's contribution to the development of new plant varieties and their impact on Brazilian agriculture

Plant breeding programs conducted by Embrapaand partners have significantly contributed to major qualitative and quantitative advances achieved by the Brazilian agriculture over the last 40 years. In this article, an overview of the diversity of crop species and the multiple goals established by Embrapas plant breeding programs is presented, highlighting some of the main contributions to the agricultural sector. The economic, social. and environmental impacts of the major cultivars released by Embrapa are reviewed and an analysis of the present and future role of the institution in cultivar improvement for tropical and subtropical regions is provided. Risks, opportunities and challenges of this endeavor are discussed, considering the recent market changes and innovations observed in the seed industry in Brazil.

Eficiência de índices fenotípicos de comprimento de raiz seminal na avaliação de plantas individuais de milho quanto à tolerância ao alumínio

The objective of this work was to verify the efficiency of the relative seminal root length (RSRL) and net seminal root length (NSRL) as phenotypic indexes for aluminum tolerance in individual maize plants. Seedlings of Al tolerant and susceptible genotypes were grown in nutrient solution containing toxic level of Al for a period of seven days, after which the values of RSRL and NSRL were determined. The results obtained when mean values of RSRL and NSRL were utilized showed that both indexes were able to discriminate tolerant from susceptible maize genotypes. However, when individual values of RSRL and NSRL were utilized, some tolerant plants scored as susceptible ones were observed, showing that the phenotypic evaluation of individual plants by both indexes is subjected to significant errors, mainly in the characterization of susceptible plants. Therefore, in studies for quantitative traits loci (QTLs) mapping for Al tolerance in maize, where these indexes are used, the most appropriate is to use F 3 families, where it is possible to obtain mean values for RSRL and NSRL and then utilize these means to represent the phenotypic values of the respective F 2 plants.

Effect of ABA and GA3 on protein mobilization in embryos and cotyledons of angico [Anadenanthera peregrina (L.) speg] seeds during germination

In this work, a woody species [A. peregrina (L.) Speg.] was studied in order to observe the effect of ABA and GA3 at the biochemical level during the process of seed germination. Embryos incubated in sucrose solution containing ABA and/or GA3 were analyzed through SDS-PAGE to observe the mobilization pattern of storage proteins during the beginning of germination. Cotyledons isolated from seeds incubated in aqueous solutions containing ABA and/or GA3, were also analyzed through SDS-PAGE and by PAGE/Activity Gels (polyacrylamide gels copolymerized with substrate for enzymes) to observe the mobilization pattern of storage proteins and protease activity after the beginning of the germination. Results of these experiments show that ABA blocks protein mobilization by inhibiting protease activity in cotyledons. This inhibition is not sufficient to prevent germination showing that the effect of ABA on germination is not dependent on protease activity. The blockage of storage protein mobilization was also observed in embryos, but no protease activity inhibition was clearly detected. ABA was able to induce the synthesis of proteins in cotyledons but not in embryos. A polypeptide with an approximate molecular weight of 17 kD, was degraded within 6 hours in control embryos, but this degradation was blocked by ABA and GA3. Using the same concentrations of ABA and GA3 on embryos and cotyledons, the effect of ABA was counteracted by GA3 in embryos, but not in cotyledons. Although the effects of ABA and GA3 were not so different from those shown in the literature, the behavior of 17 kD-polypeptide contradicts these reports suggesting that specific studies should be performed.