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.
Highlights
Casuarina equisetifolia ssp. equisetifolia belongs to the Casuarinafamily equisetifolia ssp.equisetifolia referred tomost as C.southerly equisetifolia) to the Casuarinaceae and has a wide natural(hereafter occurrence, with the partbelongs of the range in Casuarinaceae family and has a wide natural occurrence, with the most southerly part of the range in northern Australia, throughout southern Thailand, Malaysia, Indonesia, the Philippines, Melanesia northernAustralia, throughout southern Thailand, Malaysia,treeIndonesia, the Philippines, Melanesia and Polynesia (Figure1) [1]
279 alleles were identified across the 13 microsatellite loci examined in the 840 individuals representing 27 seed sources of C. equisetifolia (Table S1)
This study revealed significant differentiation among 27 seed sources within 14 natural provenances and 13 land race samples of C. equisetifolia using 13 EST-Simple Sequence Repeats (SSR) markers
Summary
Casuarina equisetifolia ssp. equisetifolia (hereafter referred to as C. equisetifolia) belongs to the Casuarinafamily equisetifolia ssp.equisetifolia referred tomost as C.southerly equisetifolia) to the Casuarinaceae and has a wide natural(hereafter occurrence, with the partbelongs of the range in Casuarinaceae family and has a wide natural occurrence, with the most southerly part of the range in northern Australia, throughout southern Thailand, Malaysia, Indonesia, the Philippines, Melanesia northernAustralia, throughout southern Thailand, Malaysia,treeIndonesia, the Philippines, Melanesia and Polynesia (Figure1) [1]. Equisetifolia referred tomost as C.southerly equisetifolia) to the Casuarinaceae and has a wide natural(hereafter occurrence, with the partbelongs of the range in Casuarinaceae family and has a wide natural occurrence, with the most southerly part of the range in northern Australia, throughout southern Thailand, Malaysia, Indonesia, the Philippines, Melanesia northern. C. equisetifolia is a nitrogen-fixing of considerable social, economic and and Polynesia (Figure 1) [1]. Equisetifolia is a nitrogen-fixing of considerable economic environmental importance in C. tropical and subtropical regions oftree the world. Million hectares and environmental importance tropical subtropicalhave regions ofplanted the world. Over two million of Casuarina plantation, most ofinwhich are and. C. equisetifolia, been for wood production, hectares of Casuarina plantation, most of which are
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