Inheritance of a Long Terminal Raceme in Soybean

Abstract

A long terminal raceme of soybean [Glycine max (L.) Merr.], identified in an F5 breeding line, could be useful in studying reproductive abscission levels and in modifying plant architecture. Information on the genetic control of the trait is unknown. Such information would provide new knowledge on the genetics of soybean morphology, and would provide an estimate of the population size needed for selection purposes. The objective of this study was to determine the inheritance of long terminal racemes in soybean. Crosses were made between two breeding lines with long terminal racemes and two commercial cultivars with short terminal racemes. Some F1 plants were grown in a glasshouse to produce F2 populations. Additional F1 plants, parents, and F2 and F3 populations were field grown. Measurements of terminal raceme length and floret number were made on field‐grown plants at the R6 developmental stage. A continuous distribution for terminal raceme length in both the F2 and F3 populationsuggests that the trait is quantitatively controlled, but some dominance for short terminal racemes seemed to be evident. Regression of the mean F3 floret number on F2 terminal raceme length provided an estimate of an increase of 1.8 florets in F3 lines for each 1‐cm increase in terminal raceme length of their F2 parent. Thus, selection for terminal raceme length may be used to indirectly select for floret number per raceme. The standard unit heritability estimate for selection of terminal raceme length on F2 plants was 61%. Only 3% of the F3 lines had a mean terminal raceme length within the range of the donor parent, indicating the need for large segregating populations for recovery of the trait.