QTL Analysis of Seed Coat Cracking in Soybean

The seed coat of soybean [Glycine max (L.) Merr] cracks under field conditions. This study was conducted to investigate the genetic basis of seed coat cracking using DNA markers. Recombinant inbred lines (RILs) were developed from a cross between a sensitive cv. Nasushirome and a tolerant cv. Enrei. Ninety-five F-6 RILs (2006) and 92 F-7 RILs (2007) with an average of 24 plants per line were grown in the field. Seed coat cracking was promoted by removing the upper 50% of pods at 40 d after anthesis. The degree of cracking of each seed was scored by a cracking index (not cracked, 0, to severely cracked, 4). Cracking index was averaged per plant and, subsequently, per line (average cracking index, Ad). Linkage mapping was performed using 114 simple sequence repeat markers and one morphological trait. The markers were associated with 18 linkage groups spanning 1232 cM. Two quantitative trait loci (QTL) for Ad, cr1 in molecular linkage group (MLG) D1b and cr2 in MLG M, were identified. The cr2 OIL was detected only in the F6 generation, whereas cr1 was identified across years and generations The cr1 had a logarithm of odds score of 4.78 (F-6) and 4.77 (F-7), accounting for 27.2 (F-6) and 23.5% (F-7) of phenotypic variation. The cr1 was not associated with seed size or maturity in F-8 near-isogenic lines. Therefore, markers around the QTL may be useful for breeding to reduce cracking symptoms without altering seed size or maturity.