Identification of parentage of Japanese pear 'Housui'

Abstract

The 84 cross combinations used in the Japanese pear breeding program in 1953-1955 were investigated to identify the parents of 'Housui' (syn. 'Hosui'). Twenty-one putative parent cultivars were investigated for their S genotypes and skin types. The S genotypes of 75 out of 84 cross combinations could not have sired 'Housui' (S3S5) because neither putative parent has an S3 nor S5 allele. Skin types of all cultivars used for 9 cross combinations selected from S genotype analysis were russet types. For this reason, 9 cross combinations are possible sources for the putative parents of 'Housui'. These 9 cross combinations were investigated by utilizing 10 SSR markers developed from Japanese and European pears. The SSR analysis indicated that only two parental crosses, 'Kousui' (syn. 'Kosui') X 'I-33' and 'I-33' X 'Kousui' were possible; the other 7 parentages had discrepancies at the 2-6 loci. The two assumed parents of 'Housui', 'Kousui' and 'I-33' were investigated by using 51 more SSR markers. A total of 61 SSR marker analyses confirmed the parent-offspring relationships because 'Housui' inherited SSR alleles from 'Kousui' and 'I-33' without any discrepancy. Chloroplast DNA (trnL-F region) was investigated to determine whether 'Kousui' or 'I-33' was the female parent. The nucleotide sequence at the trnL-F region of 'Housui' was exactly the same as that of 'Kousui', but was different from that of 'I-33'. Therefore, we conclude that 'Kousui' is the female parent of 'Housui' and 'I-33' is the male parent.