Genetic Variation in Tropical Tree Species and Plantations: A Review

Abstract

The global efforts to restore tropical forests and their productive and ecological functions through plantation forestry largely depend on the available genetic variation in the tree species used to establish the plantations. However, there is limited information on the levels and trends of the genetic variation and variability of different plantation tree species in the tropics. Therefore, this study reviews several marker-based studies that have investigated genetic variation. Most of the top economic species like Eucalyptus tereticornis and Mansonia altissima are attributed to low levels of genetic diversity, while others like Pinus caribaea and Swietenia macrophylla still exhibit high expected heterozygosity across different populations. However, the levels of genetic diversity assessed may depend on the markers used. Microsatellites, i.e., simple sequence repeats (SSRs), mostly give higher estimates when compared to other polymerase chain reaction-based markers. Other factors that typically contribute to the directional pattern of genetic variation in tropical tree species and populations include their distribution, density, seed dispersal, succession, and reproduction. Also, anthropogenic impacts like logging and fragmentation have contributed to the vast genetic base reduction of many tropical species and populations. Having adequate genetic variation within the plantation populations is significant in improving their fitness, resilience, fecundity, productivity, and other ecological functions. It also provides a basis for tree improvement and breeding in plantation forests. Although clonal forestry is becoming widespread and considered highly productive, it is attributed to specific economic, technical, and ecological risks, such as the increased spread of pests and diseases. Therefore, further discussions and recommendations to maximise genetic diversity in tropical (clonal) plantations are provided.

Diametric Structure of One Fragment of One Deciduous Seasonal Forest in Brazilian Savanna Eco Museum

“…It was calculated by dividing the number of individual stems of a diameter class by the number of individuals of the previous class. This calculation can also be done using basal area values, once every management system considers this dendrometric parameter [16] [17] [18] [19]. The model…”

Assessing Genetic Variation among Strychnos spinosa Lam. Morphotypes Using Simple Sequence Repeat Markers

“…Although the range is similar, the primers used for these species were different. The fourteen SSR markers detected a lesser total number of alleles (159) and a range of alleles per marker (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) among Strychnos spinosa morphotypes (Table 1) compared with the total number (207) and the range of alleles per marker (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) detected in Passiflora edulis Sims accessions [21]. A range in major allele frequency from 0.24 to 0.85 with an average of 0.51 in this study (Table 1) was similar to the range (0.17-0.94) and average (0.56) among Psidium genotypes [21].…”

“…Genetic variation explains the evolutionary change or adaptive potential and dictates the phenotypic variation of any tree population or species, expressed across their morphological or physiological traits [4]. It provides raw materials for the variety of growth forms, yields, and wood qualities for production, leafing, and fruiting patterns, and adaptability to environmental changes and stresses, expressed differently by different tree species [5]. Generally, plant species with a diverse gene pool as in wild species and landraces, provide the genetic resources needed for the development of the plants for production in varied/diverse environments [6].…”

“…An advantage of such a strategy is the control of environmental effects on the phenotype, which increases accuracy in computing breeding values and narrow-sense heritability estimates, provided the genotype x environment interaction and the number of genotypes that are evaluated are known [9]. Genetic diversity forms the basis of plant improvement and breeding [5].…”

“…Molecular markers have become an important instrument for characterizing wild and cultivated germplasm during the last decades [11]. Simple sequence repeat (SSR) markers are the most suitable genetic markers due to their multi-allelic nature and co-dominant inheritance, large genome coverage, small amount of starting DNA required, easy detection by polymerase chain reaction, and high polymorphism [5,12]. However, there are no microsatellite (SSR) markers available for Strychnos spinosa, and currently no study has been reported on the molecular diversity of Strychnos spinosa morphotypes.…”