AGRONOMIC PERFORMANCE OF FASCIATED SOYBEAN GENOTYPES AND THEIR ISOGENIC LINES

The fasciated soybean [Glycine max (L.) Merr.] is a morphological type caused by the recessive gene f. The original sources of the gene exhibit a broadened and flattened stem, with most of the pods at the stem tip. Fasciation has been suggested as a new gene for soybean improvement. These studies were conducted to determine (i) the agronomic performance of improved fasciated lines and (ii) the average effects of the fasciation ff genes in soybean via isogenic line comparisons. Second-cycle improved fasciated genotypes were developed from each of six crosses of first-cycle improved fasciated lines x 'Hobbit' and evaluated in local and regional field tests. Five pairs of F9 isogenic lines, ff vs. FF, were developed from each of the six crosses by maintenance of heterozygosity at the fasciation locus. Selection for seed yield among fasciated lines apparently decreased penetrance and expressivity of the ff genes. Second-cycle fasciated lines were developed that were comparable to current cultivars in seed yields in lower-yielding but not in higher-yielding environments. Seed yields of fasciated lines were not increased at higher plant densities in narrower rows. Fasciated lines were generally taller, more susceptible to lodging, and exhibited poorer quality seed as compared with commercial cultivars. The average effect of the ff gene in 30 pairs of F9 isogenic lines was +3 d plant maturity, +9 cm plant height, +2.3 plant lodging score, +14 mg seed-1 seed weight, +0.1 seed quality score, and -441 kg ha-1 seed yield. Most of the detrimental effects of the fasciated gene are probably attributable to its increased plant lodging.