Abstract
High available aluminium and low levels of calcium below the ploughed zone of the soil are limiting factors for agricultural sustainability in the Brazilian Cerrados (Savannahs). The mineral stresses compound with dry spells effect by preventing deep root growth of cultivated plants and causes yield instability. The mode of inheritance for grain yield and mineral absorption ratio of a diallel cross in soybeans [Glycine max (L.) Merrill] grown in high and low Al areas was identified. Differences among the genotypes for grain yield were more evident in the high Al, by grouping tolerant and non-tolerant genotypes for their respective arrays in the hybrids. A large proportion of genetic variance was additive for grain yield and mineral absorption ratio in both environments. High heritability values suggest that soybeans can be improved by crosses among Al-tolerant genotypes, using modified pedigree, early generation and recurrent selection schemes.
Highlights
The Brazilian Savannahs (Cerrados) cover vast areas of ferralsols in the tropics, which have free aluminium (Al) and scarcity of calcium (Ca) below the ploughed zone of the soil
The general combining ability (GCA), which measured the additive effects of genes, was superior in magnitude to the specific combining ability (SCA)
The ratio GCA/SCA was largest in the low Al environment, and lowest in the high Al environment and in the ratio high/low Al
Summary
The Brazilian Savannahs (Cerrados) cover vast areas of ferralsols in the tropics, which have free aluminium (Al) and scarcity of calcium (Ca) below the ploughed zone of the soil. These major constraints, that prevent deep root growth of cultivated plants, compounded by bad rainfall distribution, can cause yield fluctuations. The. Amendments tend to concentrate in the ploughed layer of cultivated savannah soils and only in the long run nutrients leach down into the subsoil, given there is no physical impediment. Cultivated plants, selected in these environments, possess some tolerance to toxic Al and to low levels of Ca, for deep root growth (Foy et al, 1992; Spehar, 1994a, 1995a). If the genetic factors that condition Al and low-Ca tolerances are identified, it is expected that yield in more tolerant cultivars will be buffered to weather instability.
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