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 exhi bit a broadened and flattened stem, with most of the pods at the stem tip. Fasciation has been suggested as a new gene for soybean improveme nt. These studies were conducted to determine (i) the agronomic perfor mance of improved fasciated lines and (ii) the average effects of the fasciation ff genes in soybean via isogenic line comparisons. Second-c ycle improved fasciated genotypes were developed from each of six cros ses of first-cycle improved fasciated lines x 'Hobbit' and evaluated i n 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 t he ff genes. Second-cycle fasciated lines were developed that were com parable to current cultivars in seed yields in lower-yielding but not in higher-yielding environments. Seed yields of fasciated lines were n ot increased at higher plant densities in narrower rows. Fasciated lin es were generally taller, more susceptible to lodging, and exhibited p oorer 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. Mos t of the detrimental effects of the fasciated gene are probably attrib utable to its increased plant lodging.