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Recurrent Selection for Resistance to Iron Deficiency Chlorosis in Soybeans¹

The objective of our study was to evaluate the use of recurrent selection by S₁ testing for development of a soybean [Glycine max (L.) Merr.] population with improved resistance to iron-deficiency chlorosis on calcareous soil. An intermated population was developed with the 10 most resistant cultivars or experimental lines and the 10 most resistant plant introductions available in 1975. Each cycle of selection required 1 year and included the growing of S₀ plants in Puerto Rico during the winter to obtain 100 S₁ lines, evaluation of the S₁ lines for chlorosis score on calcareous soil in Iowa, selection of the 10 most resistant lines before flowering, and recombination of selected lines for the next cycle of selection. Progress from selection was evaluated by comparing the mean performance of the parents for the cycle 0, 1, and 2 populations on calcareous soil in four Iowa environments.

There was a significant linear improvement in mean chlorosis score from cycle 0 to 2. The average genetic gain per cycle and year of 0.2 units was 9% of the cycle 0 mean. The highest frequency of resistant lines was from the cycle 2 parents. Genetic improvement in the population indicated that resistance to iron-deficiency chlorosis is influenced by genes with additive effects. The results also indicated that early-generation testing of F₂-derived or S₁ lines should be effective in development of cultivars with the desired level of resistance.

Key Words: Glycine max (L.) Merrill • Breeding • Quantitative inheritance • S₁ testing

² Graduate research assistant and professor, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011.

Received for publication October 23, 1980.