Heterodichogamy, Pollen Viability, and Seed Set in a Population of Polyploidy Cyclocarya Paliurus (Batal) Iljinskaja (Juglandaceae)

Abstract

Research Highlights: Cyclocarya paliurus, native to the subtropical region of China, is a monoecious species with a heterodichogamous mating system. Its flowering phenology and low seed success characteristics differ from other typical heterodichogamous Juglandaceae species. This could be caused by the existence of polyploidy in the population. Background and Objectives: C. paliurus has been attracting more attention as a result of its medicinal value. To meet the needs for leaf harvest, cultivation expansion is required, but this is limited by a shortage of seeds. This study aims to profile the flowering phenology and the efficacy of pollen dispersal as well as elucidate on the mechanism of low seed success in the population. Materials and Methods: The flowering phenology pattern of C. paliurus was observed in a juvenile plantation containing 835 individuals of 53 families from 8 provenances at the individual (protandry, PA and protogyny, PG) and population levels for 5 consecutive years (2014–2018). Slides with a culture medium of 10% sucrose and 0.01% boric acid were used to estimate pollen density and viability in the population, and seeds were collected from 20 randomly selected PA and PG individuals to assess seed success during 2017–2018. Results: Four flowering phenotypes and strongly skewed ratios of PA/PG and male/female occurred in the juvenile population. Sexual type and ratio changed significantly with the growth of the population over the years, showing an increasing monoecious group (11.1% to 57.2%) and a decreasing unisexual group (33.6% to 16.3%), as well as a tendency for the sexual ratio to move towards equilibrium (5.42:1 to 1.39:1 for PG:PA). Two flowering phases and bimodality in gender were displayed, as in other heterodichogamous species. However, the high overlap of inter-phases and within individuals was quite different from many previous reports. Owing to the low pollen viability of C. paliurus (~30%), low seed success was monitored in the plantation, as well as in the investigated natural populations. Conclusions: Female-bias (PG and F) and a skewed ratio of mating types corresponded to nutrient accumulation in the juvenile population. Heterodichogamy in C. paliurus was verified, but was shown to be different from other documented species in Juglandaceae. The latest finding of major tetraploidy in a natural population could explain the characteristics of the flowering phenology and seed set of C. paliurus and also give rise to more questions to be answered.

Research in Forest Biology in the Era of Climate Change and Rapid Urbanization

“…Sexual type and ratio change significantly with the growth of the population over the years, showing an increasing monoecious group and a decreasing unisexual group, as well as a tendency for the sexual ratio to move towards equilibrium. Two flowering phases and bimodality in gender are displayed, as in other heterodichogamous species, thereby verifying the presence of heterodichogamy in C. paliurus [16].…”

Morphological Characterization of Flower Buds Development and Related Gene Expression Profiling at Bud Break Stage in Heterodichogamous Cyclocarya paliurus (Batal.) lljinskaja

“…Although heterodichogamy plays an important role in plant evolution and cultivation of woody economic plants, more researches have only focused on descriptions of flowering phenology [3,10,22,23] and anatomical observations [11,12,24]. However, intrinsic mechanism controlling heterodichogamy are still unknown.…”

“…Asynchronism in differentiation of male and female flower buds in two mating types is a typical characteristic in heterodichogamous plants. Based on the previous studies [10,25], flower bud differentiation and development were divided into five stages on the basis of the process of male differentiation in PA, which was the first sexual flower to start differentiation. Physiological differentiation stage (S0), which was invisible to the naked eye, initiated after fruit setting [30].…”

“…However, the natural forest resources are mainly distributed in the mountain areas that are hard to reach or some nature reserves [8]. In addition, as a typical heterodichogamous plant, C. paliurus was characterized by high setting percentage but low seed plumpness in nature and plantation forests [9,10], which brings big challenges for breeding. Phenological observation suggested that the flowering characters of heterodichogamy in C. paliurus were the main reason for low plump seed index [11,12].…”

“…They can pave the way for future studies in other unclear flowering plants, even in heterodichogamous plants. Nowadays, publications referring to flowering characteristics of heterodichogamy are limited to phenological observations [3,10,22,23], anatomical studies [11,12,24] and a few nutrients studies [25]. Overall, the detailed molecular mechanism or genetic elements on regulation of floral organ differentiation and development in C. paliurus remains elusive.…”