COMPARATIVE STABILITY OF 40 INDETERMINATE AND SEMIDETERMINATE SOYBEANLINES

Indeterminate, semideterminate, and determinate soybean [Glycine max ( L.) Merr.] cultivars differ primarily in the timing of cessation of ma in stem growth. This timing affects mature plant height, lodging resis tance, and the length of the flowering and reproductive periods. In th e northern soybean production areas of North America, indeterminate (D t1 Dt1 dt2 dt2) cultivars predominate, although several studies have s hown that agronomic performance of soybean lines with a semideterminat e (Dt1 Dt1 Dt2 Dt2) stem type is similar. A previous comparison of a f ew indeterminate and semideterminate lines tested across eight Illinoi s environments provided evidence that the semideterminate might have l ess yield stability than the indeterminate plant type. The general sca rcity of commercially available semideterminate cultivars may be the r esult of this potential yield instability. This study utilized a large number of genotypes to further evaluate the relative stability of the semideterminate in comparison with the indeterminate stem type. From two crosses, 20 pairs of F3-derived sister lines (Maturity Group I-II) differing for stem termination were evaluated across nine environment s for yield and plant height. Genotype x environment variance componen ts were significant and of similar magnitude for semideterminate and i ndeterminate lines, indicating that progress from selection should be similar for each. Stability analysis identified eight indeterminate an d nine semideterminate lines as stable for yield. Ten semideterminate, but only six indeterminate lines, had significant deviations from reg ression for plant height. Overall, the results indicate that stability should not be a barrier to breeding progress for the semideterminate plant type in areas where Maturity Groups I and II soybean are grown.