RELATIONSHIPS BETWEEN THE FAN ALLELE AND AGRONOMIC TRAITS IN SOYBEAN

Normal levels of linolenic acid (70-80 g kg-1) in soybean [Glycine mar (L.) Merr.] oil adversely affect oil flavor and stability. The mutation-induced line C1640 has half the normal level of linolenic acid (37 g kg-1), but is 24% lower yielding than 'Century', from which it was selected. This study was conducted to determine if there are genetic relationships between agronomic traits and the fan allele for low linolenic acid identified in C1640. Century and 'Harper', both with the FanFan alleles for normal 18:3, were crossed with C1640 containing the fanfan alleles for low 18:3. Both FanFan and fanfan segregates from the two crosses were evaluated for agronomic traits and linolenic acid in replicated tests over a 2-yr period on a Chalmers soil (fine-silty, mixed, mesic Typic Haplaquoll) at the Purdue University Agronomy Research Center near West Lafayette, IN. The fanfan segregates in the Century x C1640 cross averaged slightly higher in seed yield and taller in plant height than the FanFan segregates. In the Harper x C1640 cross,fanfan segregates averaged 1 d later in maturity than FanFan segregates. Mean values for FanFan and fanfan segregates for other traits in both crosses were essentially the same. These data indicate that there are no associations between the fanfan alleles and those agronomic traits needed in commercial soybean cultivars with low levels of linolenic acid. Apparently the low yield of C1640 is controlled by genetic changes independent of the mutation for low 18:3. Regression of linolenic acid level on maturity dates for both FanFan and fanfan segregates in the Harper x C1640 cross show that segregates of both genotypes tended to have increased linolenic acid at later maturity dates. This could be attributed to the cooler temperatures during seed maturation to which the later maturing segregates were exposed.