No abstract

Two soybean varieties (Glycine max) were grown in nutrient solution to investigate their response to manganese toxicity at two different temperature regimes. Dry matter yields of both varieties were markedly reduced by lower temperature (21 °C day/18°C night). At these temperatures leaf crinkle symptoms of Mn toxicity were very severe on Bragg and moderate on Lee at high levels of Mn in solution (15 ppm). However increasing the temperature to 33°C day/28°C night completely eliminated symptoms on both varieties. High levels (15 ppm) of Mn in nutrient solution decreased yields of both varieties at low temperature with Bragg showing the greater reduction. At high temperature neither variety showed yield reductions at 15 ppm Mn.Higher concentrations of Mn in shoots and roots were obtained at higher temperature, indicating that increased tolerance was not associated with lower plant Mn levels. Lee consistantly contained higher levels of Mn in the shoots than Bragg in the 15 ppm Mn solution at both temperatures although appearing to be more tolerant at low temperatures.The implications of these results for environmental effects on the expression of Mn toxicity in the field are discussed.

Soybean [Glycine max (L.) Merr.] cultivars show differential tolerance to high manganese (Mn) supply levels as evidenced by severity of symptoms and reductions in yield. Crosses of the tolerant cv. ‘Lee’ with a susceptible cv. ‘Bragg’ gave F1 plants with only moderate Mn toxicity symptoms and the F2 generation showed a continuous distribution in symptoms that was skewed towards tolerance. The F6 progeny from a cross of ‘Amredo’ (tolerant) and Bragg (susceptible) had a bimodal distribution. Tolerance to high Mn levels is an inherited character.

Three field experiments studying the effect of chlormequat (CCC) on the grain yield of spring wheat and the quality of the grain for baking purposes were made. I n the first, CCC applied as a spray during the stage of rapid internode elongation proved more successful than application as a mixture with superphosphate drilled with the seed at sowing. Both methods prevented lodging and the depression of yield which occurred in the control plots. I n the other two experiments the sole method of CCC application was by spraying.In all three experiments CCC-treated plots had more ears per unit area and grains per ear than control plots; the one exception being at the lowest plant density derived from a seeding rate of 24 kg/ha. CCC helped prevent weather damage to the grain and as a result baking performance of the flour from treated plots was superior to that from the untreated plots. I N T R O D U C T I O NIn Europe much information has been collected on the use of chlormequat (CCC : 2-chloroethyl-trimethyl-ammonium chloride) for the commercial production of wheat. This has been well reviewed by Humphries (1968) and at the joint meeting of the cereal and physiology sections of Eucarpia, Wageningen, 1967, at which the introductory paper was given by Morgan (1968).The general principles that have emerged from the published results are that ccc (a) may be used to control lodging induced by weather, disease, or excessive vegetative growth resulting from large amounts of nitrogenous fertilizer, (b) may increase the drought tolerance of plants when adequate moisture is not available, (c) sometimes produces increases in grain yield through either or all of the following effects: (i) increasing the survival of tillers to form ears, (ii) increasing the number of grains per ear, (iii) delaying senescence of the upper parts of the plant and hence extending the grain-filling period.