Evaluation of inbred maize lines for aluminum tolerance in nutrient solution.

A number of plant measurements were evaluated for their ability to differentiate genotypes for Al tolerance in nutrient solution culture. The best traits proved to be seminal and adventitious root lengths. On this basis, Brazilian inbred lines were shown to be more tolernat of Al than those from the USA. In most lines, root lengths decreased as the Al concentrations used, but in some Brazilian lines root length was unaffected. Al tolerance increased if P was included in the nutrient solution. The combination of 185 umol P/litre in the nutrient solution was the best for evaluationg genotypes for Al tolerance

Comparisons of maize populations for aluminum tolerance in nutrient solutions.

The original Brazilian base population Composto Amplo (CA) and a population (4CA) from the 4th cycle of selection from it for Al tolerance on an acid Brazilian Oxisol soil were compared with the population Hays Golden, Nebraska B Synthetic, Corn Belt X Brazilian and Corn Belt X Caribbean when grown in nutrient solutions containing 241 umol Al/litre Root length was slightly greater in CA than in 4CA and both had considerably longer roots than the other populations. The selection of CA for Al tolerance decreased the frequency of the most tolerant plants in favour of plants of intermediate tolerance. The CA and 4CA populations had a higher frequency of genes for Al tolerance than the other populations. The Corn Belt X Brazilian population consistently ranked higher in Al tolerance than Hays Golden and Nebrasla B synthetic, indicating that the introgression of Brazilian germplasm increased tolerance. CA and 4CA roots had lower Al concentrations, but similar Al contents to those of Hays Golden and Nebraska B Synthetic. Other differences in element concentrations and contents between the 2 sets of populations were observed, while the hybrid populations were intermediate between their tropical and temperate parental populations for these factors

Inheritance of aluminum tolerance in maize.

In a set of 3 experiments, a number of parental lines and various of their hybrid and backcross generations (from crosses of tolerant and sensitive lines) were raised in nutrient solution containing 195 umol Al/litre. An analysis of relative seminal root lengths showed than additive gene effects contributed most to genetic variation in Al tolerance, with dominance effects accounting for only half as much varation. Epistatic effects were minor. The frequency distributions of tolerance in the F2 were typical of a quantitatively inherited trait. There was a tendency for non-tolerance to be dominant over tolerance although this was not consistent. Analysis of the F1 from a diallel cross among 8 inbred lines indicated that general combining ability variance explained most of the variation, but specific combining ability effects were significant in each case

Seleção de milho para tolerância a alumínio.

Solos acidos sao frequentemente em areas tropicais do mundo. Os solos que mais atingem a adaptacao de plantas nessas regioes sao os Oxisolos, que ocupam 8,11% das terras do planeta. Sao solos muito intemperizados e tem baixa capacidade de troca de cations. E comum apresentarem deficiencia de Ca e Mg, presenca de aluminio trocavel e possibilidade de fixacao de fosfatos em minerais como sesquioxidos. Uma alta saturacao de aluminio no solo e toxico para o desenvolvimento de plantas. Aluminio afeta muitos processos fisiologicos, bioquimicos e metabolicos da planta e pode causar injurias as raizes. Metodologia de solucao nutritiva e teste no campo tem sido desenvolvidas para uso em melhoramento. Ja foi dectada variabilidade para tolerancia a aluminio em milho e tolerancia a aluminio tem sido desenvolvidos e a tolerancia tem sido adicionada a genotipos de alta produtividade e estaveis. Estuda-se tambem a associacao de tolerancia a aluminio com eficiencia de fosforo em solos acidos

Adaptaciones morfologicas y fisiologicas en plantas de maiz sometidas a deficiencia de oxigeno en el suelo.

El maiz en el Brasil se cultiva normalmente en el verano, cuando lluvias intensas son comunes y la saturacion o encharcamiento del perfil del suelo suele ocurrir. En condiciones de areas bajo riego, despues de la cosecha del arroz, el cultivo del maiz puede sufrir los efectos del encharcamiento por la elevacion del nivel freatico, por lluvias ocasionales y por la infiltracion de los canales de riego. En estas circunstancias, los cultivares que presentan tolerancia al "stress" de oxigeno tienen mayores posibilidades de resistir, minimizando los riesgos de perdidas. El cultivo del maiz ha sido poco estudiado en estas circunstancias y las experiencias actuales muestran que, a pesar de importantes, los trabajos conducidos en el campo con el objetivo de evaluar tolerancia son de dificil ejecucion dado que muchos factores no pueden ser controlados adecuadamente. Considerando la inmensa area del territorio brasileno, potencialmente utilizable para el cultivo del maiz que esta sujeta a deficiencias acasionales de oxigeno, el Centro Nacional de Investigacion de Maiz y Sorgo de la Empresa Brasilena de Investigacion Agropecuaria (CNPMS/EMBRAPA), viene desarrollando trabajos para detectar, cuantificar y manipular adaptaciones morfologicas y fisiologicas en las plantas de maiz sometidas a deficiencia de oxigeno. El presente trabajo tiene por objetivo reunir informaciones basicas sobre sistemas de suelo bajo condiciones de ausencia de oxigeno (anoxia) y, ademas, estudiar la reaccion de las plantas sometidas a esta condicion