Search Results (2)

Fraxinus platypoda Oliv. (Oleaceae), an ecologically and economically valuable tree species with key distribution areas in northwestern China, faces conservation challenges due to its fragmented groups and scarce individual numbers. To investigate the genetic consequences of this demographic crisis, we analyzed 65 individuals from 11 natural groups in this region using whole-genome resequencing. We identified a total of 60,503,092 single nucleotide polymorphisms (SNPs), and after further filtering, retained 3,394,299 SNPs for subsequent analysis. Population structure analysis (Neighbor-Joining tree, STRUCTURE, and kinship coefficients) revealed two distinct genetic clusters (K = 2), with principal component analysis (PCA) confirming this subdivision. Cluster I, composed of eight individuals from Groups 3, 5, 8, and 11, is highly differentiated from Cluster II and may be ancestral to it. Among the 11 groups, Groups 3 and 11 show a high genetic diversity and differentiation, with Tajima’s D > 0, indicating a long evolutionary history and balancing selection. The remaining nine groups have a low diversity, low differentiation, and frequent gene flow, with Tajima’s D < 0, suggesting directional selection. A mantel test showed no significant link between genetic variation and geographic isolation (p = 0.460). The high differentiation of Cluster I and gene flow of Cluster II are maintained by factors like evolutionary history and reproductive systems. Groups 3 and 11 are highlighted as important genetic resources deserving priority protection. This study offers key genomic data for conserving fragmented tree species and future adaptability research. Full article

Androdioecy is a rare reproductive system. Fraxinus platypoda, a woody canopy species in Japan’s mountainous riparian zones, is described as a morphologically androdioecious species. In this study, we tried to detect whether F. platypoda is also functionally androdioecious. We analyzed its sexual expression, seed development, pollen morphology and germination ability, pollination systems, and mast flowering behavior. We found that the hermaphrodite trees are andromonoecious, with inflorescences bearing male and hermaphroditic flowers, whereas male individuals had only male flowers. Pollen morphology was identical in male flowers, in hermaphrodite flowers of an andromonoecious individual, and in male flowers of male individuals. Pollen from both types of individuals was capable of germination both ex vivo (on nutrient medium) and in vivo in pollination experiments. However, compared with pollen from andromonoecious trees, pollen from male trees showed a higher germination rate. The self-pollination rate of bagged hermaphroditic flowers was almost zero. The fruit set rate following cross-pollination with male pollen from a male tree was higher than that following natural pollination, whereas the rate with hermaphroditic pollen was the same. The flowering and fruiting of F. platypoda have fluctuated over 17 years; the flowering of the two types of sexual individuals exhibited clear synchronization during this period. The frequency of male individuals within the populations is 50%. The maintenance of such a proportion of males in populations of the self-incompatible F. platypoda is either indicative of a true androdioecious species with a diallelic self-incompatibility system or a cryptic-dioecious species. This alternative is discussed here. Full article