Salinity and Defoliation Effects on Soybean Growth

ABSTRACT

An experiment was conducted to determine if salinity stress alters the response and tolerance of soybean to defoliation. Four soybean [Glycine max(L.) Merr.] cultivars (‘Tachiutaka,’ ‘Tousan 69,’ ‘Dare’ and ‘Enrei’) in a growth chamber were exposed to two salinity treatments (0 and 40 mM NaCl) and two defoliation treatments (with and without defoliation). The interactive effects of salinity stress and defoliation on growth rate, leaf expansion, photosynthetic gas exchange, and sodium (Na⁺) accumulation were determined. The decrease in growth rate resulting from defoliation was more pronounced in plants grown under salinity stress than in those grown without the stress. Without salinity stress, defoliated plants of all four cultivars had leaf-expansion similar rates to those of the undefoliated ones, but the photosynthetic rates of their remaining leaves were higher than those of undefoliated plants. However, with salinity stress, defoliated ‘Tachiutaka’ and ‘Tousa 69’ had lower leaf expansion and photosynthetic rates than undefoliated plants. For cultivars ‘Dare’ and ‘Enrei,’ the defoliated plants had leaf-expansion rates similar to undefoliated ones, but the photosynthetic rate of the remaining leaves did not increase. Except for cultivar ‘Dare,’ defoliated plants grown under salinity stress had higher Na⁺ accumulation in leaves than undefoliated ones, and this result may be related to slow leaf expansion and photosynthesis. Salinity stress negatively affects soybean response and tolerance of defoliation, and the effects varied according to the salt tolerance of the cultivar.

Keywords:

• defoliation
• growth
• salinity stress
• soybean

Notes

∗∗,∗ Significant at the 0.05 and 0.01 probability levels. ns, not significant.

∗∗ Significant at the 0.05 and 0.01 probability levels. ns, not significant.

∗ Significant at the 0.05 and 0.01 probability levels. ns, not significant.

⁺ Within columns, means followed by the same letter are not significantly different (P < 0.05).

∗∗Significant at the 0.05 and 0.01 probability levels. ns, not significant.

∗Significant at the 0.05 and 0.01 probability levels. ns, not significant.

⁺ Within columns, means followed by the same letter are not significantly different (P < 0.05).