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Wageningen Universiteit (1993)

Analysis of aluminium sensitivity in sorghum (Sorghum bicolor (L.) Moench) genotypes

Tan, K.

Titre : Analysis of aluminium sensitivity in sorghum (Sorghum bicolor (L.) Moench) genotypes

Auteur : Tan, K.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 1993

Twelve genotypes of sorghum ( Sorghum bicolor (L.) Moench) differing in Al sensitivity were grown in an acid soil (with additions of lime or MgSO 4 ) and in nutrient solutions (with or without Al at constant pH) for periods between 14 and 35 days. The objective was the identification of the factors controlling dry matter yield of sorghum under different growth conditions. In both media Al was the major constraint, restricting growth in two independent ways : (1) by inducing Mg deficiency and (2) via damaging the roots ( i.e. by giving them a stubby and discolorated appearance and by reducing their specific root length, m g -1dry root). The sensitivities of the genotypes against Al-induced Mg deficiency and Al-induced root damage were not correlated. At moderate acidity (pH around 4.8), Mg deficiency dominantly limited growth whilst at a higher acidity (pH 4.2) root damage overruled Mg deficiency in its negative effect on growth. At pH 4.8, addition of Mg improved growth by reducing the degree of Mg deficiency. At pH 4.2, Mg improved growth mainly by preventing the roots from Al- induced damage. Several external factors modified the AI sensitivity of the genotypes by strengthening or weakening the negative effects of Al on Mg nutrition and root development. At pH 4.2, Ca and NH 4 both counteracted AI-induced root damage but aggravated Al-induced Mg deficiency. The contrary was true for NO 3 . When the concentration of soluble Al was kept approximately constant at 15 μM, both Al-induced root damage and Mg deficiency were aggravated by acidity in the range pH 3.9-4.8. Aluminium toxicity in sorghum grown in nutrient solution was independent of P deficiency, although an increased P supply partly eliminated Al phytotoxicity. The results stress the importance of both Al and Mg ions and their interactions in determining growth response of sorghum and other cereals to acid soils.

Mots clés : crop damage / soil pollution / soil toxicity / soil salinity / sorghum bicolor / toxic substances / chemistry / indicator plants / toxins / plants / soil / aluminium / aluminum / yield increases / yield losses / yields / acid soils / acid sulfate soils / chemical factors

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