Stem Cutoff Enhances Selection for Improved Iron Efficiency of Soybean¹

Abstract

Five cycles of recurrent selection for iron (Fe) efficiency resulted in a soybean [ Glycine mar (L.) Merr.] population with a high percentage of segregates that showed little or no yellowing when grown on calcareous soil in the field. Further improvement for Fe efficiency in the population is not possible unless a method is available to enhance the expression of genetic variability. This study was conducted to evaluate stem cutoff as a method for enhancing the expression of genetic variability for Fe efficiency in a population with a high proportion of Fe‐efficient segregates. The parents of Cycles 0 through 5 and 100 S 0 ‐derived lines from the Cycle 5 population of AP9 were grown on calcareous soil. At stage V3, when the second trifoliolate leaf was fully developed, the entries were scored for chlorosis (1 = no yellowing to 5 = severe yellowing); then the main stem was cut off above the unifoliolate node. The new leaves produced were evaluated for chlorosis 2 weeks after treatment. Stem cutoff significantly increased the chlorosis of the parents and S 0 ‐derived lines by an average score of 1.4. The rate of genetic improvement from Cycle 0 to Cycle 5 was the same before and after treatment, with an average decrease in chlorosis score of −0.16 per cycle before treatment and −0.15 per cycle after treatment. Genetic variability among the 100 random lines was significantly increased by stem cutoff. The genotypic variance component estimate was 0.02 ± 0.01 before treatment and 0.10 ± 0.02 after treatment. The results indicated that stem cutoff is an effective method of increasing chlorosis in a population with a high level of Fe efficiency, permitting selection for further improvement of the character.