Characteristics of Phenotypic Variation of Malus Pollen at Infrageneric Scale

Pollen carries extensive genetic information, which may provide clues regarding the kinship of <i>Malus,</i> whose genetic relationships are complex. In this study, the phenotypic variation of pollen from 107 <i>Malus</i> taxa was investigated using combined methods of intraspecific/interspecific uniformity testing, cluster analysis, and Pearson correlation analysis. The family aggregation distributions in <i>Malus</i> sections, species, and cultivars were analyzed to infer their pedigree relationships. The results showed that (1) compared with pollen size and morphology, aberrant pollen rate and ornamentation were highly interspecifically differentiated, but ornamentation was also intraspecifically unstable, especially perforation densities (c.v.¯ > 15%). (2) The pollen alteration direction from the original to the evolutionary population of <i>Malus</i> was large to small, with elliptic to rectangular morphologies, large and compact to small and sparse ridges, and low to high perforation densities. However, there was no significant change in pollen size. (3) The 107 studied taxa were divided into four groups. <i>Malus</i> species were relatively clustered in the same section, while homologous cultivars showed evidence of family aggregation distribution characteristics (92.60% of cultivars were clustered with their parents). (4) <i>M</i>. <i>baccata</i> and <i>M</i>. <i>pumilar</i> var. <i>neidzwetzkyana</i> were high-frequency parents, participating in 38.7% and 20.7% of cross-breeding, respectively. Overall, this study provides a reference for identifying <i>Malus</i>' pedigree relationship.