New Allele at the Fan Locus in the Soybean Line A5
The soybean [Glycine max (L.) Merr.] line A5 has a low content of linolenic acid in the seed oil. Our objective was to determine if alleles at the Fan locus were influencing this trait in A5. To reduce environmental influences, the study was conducted indoors. Crosses were made between A5 and the low linolenic acid lines C1640 (fan/fan) and N78-2245 (Fan/Fan). The F2 progeny of A5 ✕ N78-2245, N78-2245 ✕ A5, and N78-2245 ✕ C1640 segregated in bimodal patterns for linolenic acid content, each consistent with a 3:1 ratio. The F2 patterns were confirmed by assays of F3 progeny. There was no segregation for linolenic acid content in the F2 progeny of A5 ✕ C1640. These observations indicated that A5 ✕ N78-2245, and N78-2245 ✕ A5 segregated for alleles at the Fan locus. The pattern of low linolenic acid content showed that the Fan and Idh2 loci were linked at distances of 25.2 ± 3.5 units for A5 ✕ N78-2245, 24.3 ± 3.4 for N78-2245 ✕ AS, and 24.7 ± 3.5 for N78-2245 ✕ C1640. These results were all consistent with an allele at the Fan locus being the primary factor responsible for the low linolenic acid content in A5. The allele in A5 has been designated fan(AS). The fan(AS) allele appeared to be in two F4 lines from A5 ✕ N78-2245 that were characterized by a mean linolenic acid content <25 g kg−1 when grown under 16 h daylength at 28/22°C day/night. The complete genetic basis of this phenotype is receiving further study.
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