Identification of the S genotype of Malus plants will greatly promote the discovery of new genes, the cultivation and
production of apple, the breeding of new varieties, and the origin and
evolution of self-incompatibility in Malus plants. In this experiment, 88 Malus germplasm
resources, such as Aihuahong, Xishuhaitang, and Reguanzi, were used as
materials. Seven gene-specific primer
combinations were used in the genotype identification. PCR amplification using leaf DNA produced a
single S-RNase gene fragment in all materials. The results revealed that 70 of the
identified materials obtained a complete S-RNase genotype, while only
one S-RNase gene was found in 18 of them. Through homology comparison and analysis, 13 S-RNase genotypes were obtained: S1S2 (Aihuahong, etc.), S1S28 (Xixian Haitang, etc.), S1S51 (Hebei
Pingdinghaitang), S1S3 (Xiangyangcun Daguo, etc.), S2S3 (Zhaiyehaitang, etc.), S3S51 (Xishan 1), S3S28 (Huangselihaerde, etc.), S2S28 (Honghaitang, etc.), S4S28 (Bo 11), S7S28 (Jiuquan Shaguo), S10Se (Dongchengguan 13), S10S21 (Dongxiangjiao) and SeS51 (Xiongyue Haitang). Simultaneously, the frequency of the S gene in the tested materials was analyzed.
The findings revealed that different S genes had varying
frequencies in Malus resources, as well as varying frequencies between
intraspecific and interspecific. S3 had the highest frequency of 68.18%, followed by S1 (42.04%). In addition, the phylogenetic
tree and origin evolution analysis revealed that the S gene
differentiation was completed prior to the formation of various apple species,
that cultivated species also evolved new S genes, and that the S50 gene is the oldest S allele in Malus plants. The S1, S29,
and S33 genes in apple-cultivated species, on the other hand,
may have originated in M. sieversii, M. hupehensis,
and M. kansuensis, respectively.
In addition to M. sieversii, M. kansuensis and M. sikkimensis may have also played a role in the origin and
evolution of some Chinese apples.