RECOMBINATION RATES OF SOYBEAN VARIETIES FROM DIFFERENT PERIODS OF INTRODUCTION AND RELEASE

Theory predicts that selection for adaptability during the short term also favors selection for a reduced recombination rate in the populati on. The objective of this study was to test whether the cyclic short-t erm selection which has taken place in soybean breeding programs in th e USA since the introduction of the crop has measurably reduced recomb ination frequencies. Thirteen soybean varieties separated into four di fferent release periods (prior to 1940, 1940-1954, 1955-1969, after 19 70) were evaluated for their recombination frequencies within three lo cus pairs. Recombination frequencies among the individual varieties ra nged from 7.6 to 24.1 % at the p1r locus pair, from 20.9 to 30.1 % at the lnp2 locus pair, and from 28.7 to 41.6 % at the dt1l1 locus pair. Recombination frequencies were significantly different among varieties within a release period for the p1r and lnp2 locus pairs, but recombi nation frequencies did not differ among release periods for any locus pair. Thus, apparently, plant breeders have developed soybean varietie s with improved adaptation without influencing recombination rates.