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Nodulation and Early Growth of Soybean Mutants with Increased Nodulation Capacity Under Acid Soil Infertility Factors

Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602

D. G. Edwards and C. J. Asher

Dep. of Agriculture, Univ. of Queensland, St. Lucia, Queensland 4067, Australia

B. J. Carroll and P. M. Gresshoff

Dep. of Botany, Australian Natl. Univ., Canberra, A.C.T. 2601, Australia

^* Corresponding author

Nitrate tolerant symbiotic (nts) mutants have exhibited a greatly increased capacity for nodulation under nonacidic conditions. To evaluate the potential for growing the mutants in acid soils, the nodulation and growth of the mutants were investigated in this study under acid soil infertility factors. The effects of pH, Ca, and Al on nodulation and early growth of ‘Bragg’ soybean [Glycine max (L.) Merr.] and two mutants (nts382 and nts1116) with increased nodulation capacity were evaluated in nutrient solution experiments. In both experiments, the mutants nodulated more quickly than Bragg under conditions conducive to nodulation. The first experiment examined effects of pH (4.0, 4.5, 5.0, and 6.0) and Ca concentration (0.05 and 1.0 mM). At pH 4.0, nodulation was completely inhibited in all lines at 0.05 mM Ca, but only in Bragg at 1.0 mM Ca. Nodule number and nodule weight per plant increased significantly with an increase in solution pH from 4.0 to 5.0, and were much greater in the mutants than in Bragg, particularly at pH 4.5,5.0, and 6.0. Shoot and root weights in Bragg and ntslll6 generally increased with an increase in solution pH. However, there was a strong reduction in shoot and root weight of nts382 at pH 5.0 and 6.0 associated with greatly increased nodule numbers. The second experiment examined the effects of the sum of activities of monomeric Al species (a_{Al mono}) up to 70 iiM. The mutants nodulated much more prolifically than Bragg in solutions with a Al mono 32 µM, and only failed to nodulate at 70 µM. Bragg failed to nodulate at 32 µM. Stronger inhibitory effects of lower a Al mono were observed on nodule number and nodule weight than on early shoot growth. Thus, a a Al mono from 0.1 to 0.4 µM reduced nodule number and weight by 10%, whereas 5 to 10 µM was required to reduce shoot weight by 10%.

Received for publication October 5, 1987.