V3 and V4 region analysis of 18S rRNA genes in natural strains of S. fimicola and their F1 progeny. M, DNA marker; S3, parental strain; 1, 2 and 3, F1 progeny of S3; N5, parental strain; 4, 5, 6 and 7, F1 progeny of N5; Neg., negative control without genomic DNA