Analyses of Genetic Diversity, Differentiation and Geographic Origin of Natural Provenances and Land Races of Casuarina equisetifolia Based on EST-SSR Markers

Abstract

Research Highlights: High variation of genetic diversity and differentiation among 27 seed sources within 14 natural provenances and 13 land race samples of Casuarina equisetifolia were found. High proportions of monoecious individuals may be present in some populations, as indicated by severe heterozytote deficiency and inbreeding found in many provenances and land races. The most probable origins of the land races were inferred according to the values of pairwise provenance differentiation and Nei’s genetic distances. Targeted introductions and testing of unrelated new accessions of C. equisetifolia from the Pacific and Philippines was proposed to identify Ralstonia-resistant genotypes. Background and Objectives: Casuarina equisetifolia was introduced to China a hundred years ago and has become a critically important tree species in coastal protection since the 1950s. Despite its importance, patterns of genetic variation, genetic relationships among natural provenances and probable origins of the land races remain unresolved. This has become a concern in China where Ralstonia solanacearum bacterial wilt has devastated plantations that are known to be from a narrow genetic base that urgently needs to be broadened. Materials and Methods: Fourteen natural provenances from Australia, Pacific islands and Southeast Asia, and 13 land race samples from parts of Asia and Africa outside the natural range were genotyped using 13 SSR (Simple Sequence Repeats) markers to characterize their allelic variation and genetic relationship. Results: Significant genetic diversity and differentiation among 27 seed sources within 14 provenances and 13 land race samples of C. equisetifolia was indicated. Significant heterozygote deficiency and inbreeding was indicated for a number of provenances, perhaps indicating a high proportion of monoecious parents in these populations. The most probable origins of the land races of the introduced countries were suggested according to the values of pairwise provenance differentiation (FST) and Nei’s genetic distances. Conclusions: We found significant genetic diversity and genetic differentiation among seed sources of C. equisetifolia. While individual land races do not appear to lack diversity, we were able to infer the origins of some, allowing targeted introductions of unrelated material to be made. In the case of the Chinese land race, targeting and testing new accessions from the Pacific and the Philippines may be a good strategy to identify Ralstonia-resistant genotypes.

Effect of Seed Extraction Period and Germination Temperature on Viability of Pinus patula Under Controlled Conditions

“…Previous studies have shown that both environmental and genetic factors influence the potential of trees to produce fertile quality seeds whereby depending on the tree species, seed germination varied according to latitude, elevation, soil moisture, soil nutrient, temperature, type and density of plant cover, and degree of habitat disturbance of the site [49,50]. Location of seed at the time of maturity plays an important role in determining a forest tree's potential for seed quality and seed fertility [51][52][53].…”

Evaluation of genetic diversity and population structure of Fragaria nilgerrensis using EST-SSR markers

“…The mean Fis > 0 and the lower observed heterozygosity than the expected heterozygosity at species level indicates lack of heterozygosity in the populations of F. nilgerrensis. It was reported that lack of heterozygotes among the related individuals is due to either random mating with a restricted paternal pollen pool, or non-random mating (Zhang et al, 2020). Both a self-compatible breeding system and clonal propagation in F. nilgerrensis could cause the low outcrossing rates and heterozygosity.…”

Influence of Cone Physical Characteristics and Extraction Exposure Period on Seed Yield of Pinus patula

“…Cone and seed production in other pines has also been shown to be positively influenced by larger basal areas [22,39]. Other factors such as stand density, climatic variations, and the morphological parameters of trees also influence their reproductive capacity [40][41][42]. It was reported that in some pines (for example Aleppo), sub-humid climate enhances cone production over semi-arid conditions.…”