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A Technique to Determine Iron Efficiency in Plants¹

ABSTRACT

Soil tests should predict crop response to fertilization. In the case of Fe, plant factors seem to affect the use of Fe by the plant; thus, soil tests may not be reliable. Use of soil Fe by plants is genetically controlled by an adaptive mechanism which is activated in Fe-efficient plants in response to Fe-stress, but remains inactive if Fe is sufficient. Fe-inefficient plants develop less Fe-stress response than Fe-efficient plants. Using this range of Fe-stress response in plants as a basis, we developed a technique to screen plants for Fe efficiency.

A limited supply of Fe and some control of pH in the growth medium were required in this technique. The pH was controlled by using nutrient solutions, N only as No₃, and N as NH₄ and NO₃, and by varying the CaCO₃ and P concentrations in the solutions. The optimum supply of Fe (0.2 mg Fe/liter) was determined by growing the plants at different Fe concentrations.

Four Fe-inefficient and four Fe-efficient plant varieties, representing four plant species, were used as test plants. The plants were screened in mixed cultures and were rated in order of greatest Fe efficiency as follows:

T3238FER tomato (Lycopersicon esculentum Mill.) Hawkeye soybean (Glycine max (L.) Merr.) > W59 Corn (Zea mays L.) > Pioneer 846 sorghum (Sorghum bicolor (L.) Moench) > PI-54619-5-1 soybean > Wheatland sorghum > ys₁/ys₁ corn > T3238fer tomato.

Green plants contained more and chlorotic plants contained < 43 µg Fe/g, but the degree of Fe-chlorosis was the best index of Fe-efficiency. A suggested sequence for screening plants for Fe-efficiency is presented.

¹ Contribution from USDA, ARS, Plant Stress Laboratory, Beltsville, MD 20705.

² Soil Scientist and Research Technician, respectively, USDA, ARS, Plant Stress Laboratory, Beltsville, MD 20705.

Received for publication August 27, 1975. Accepted for publication January 8, 1976.