Screening Soybean Cultivars for Resistance to Iron-Deficiency Chlorosis in Culture Solutions Containing Magnesium or Sodium Bicarbonate

ABSTRACT

Hydroponic culture solutions containing bicarbonate (HCO₃ ⁻) may be used to screen crops such as soybeans (Glycine max) for resistance to iron (Fe) deficiency or chlorosis. Some successful methods use sodium bicarbonate (NaHCO₃) in combination with elevated partial pressures of carbon dioxide (CO₂) to buffer pH and elevate bicarbonate. Replacing NaHCO₃ with magnesium bicarbonate [Mg(HCO₃)₂] as the form of bicarbonate alkalinity has the potential to produce culture solutions that simulate soil solutions more closely and eliminate any potential for specific sodium (Na) toxicities in sensitive plants. A modified screening solution based on Mg(HCO₃)₂-CO₂ was tested against the successful NaHCO₃-CO₂ method, using three soybean varieties of known resistance to Fe-deficiency chlorosis. Alkalinity was 10 mM [added as NaHCO₃ or Mg(HCO₃)₂], solutions were aerated with 3% CO₂, and Fe was provided as FeDTPA (diethylenetriamine-pentaacetic acid) at 15 μM (low Fe) or 60 μM (adequate Fe). Leaf chlorophyll, visual chlorosis index, and leaf Fe concentration were closely related. Solutions based on NaHCO₃ or Mg(HCO₃)₂ provided identical chlorosis-susceptibility rankings for the three cultivars.

Keywords:

• Bicarbonate-induced chlorosis
• iron deficiency
• plant nutrition
• chlorosis screening
• bicarbonate
• sodium
• magnesium
• nutrient solution
• soybean
• Glycine max

Notes

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∗Mean total chlorophyll in trifoliolate leaves of four plants of a cultivar within an Fe × buffer treatment. LSD is given at p = 0.05 level for each leaf for comparison of cultivars within a treatment. There were no significant differences between buffers within an Fe treatment for any genotype (see Table 1).

∗Median and (interquartile range) for visual chlorosis index (0–5 scale; see Materials and Methods) for the trifoliolate leaves of the four plants in each buffer × Fe treatment. For comparison of cultivars within an Fe × buffer treatment, the VCI values for a trifoliolate leaf followed by the same letter within a column are not significantly different based on relative treatment effects estimated by the method of Shah and Madden (2004). There were no significant pair-wise differences between buffers within an Fe treatment for any genotype (see Table 1).

∗Mean total Fe in trifoliolate leaves of four plants of a cultivar within an Fe × buffer treatment. LSD is given at p = 0.05 level for each leaf for comparison of cultivars within a treatment. There were no significant differences between buffers within an Fe treatment for any genotype (see Table 1)