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Habitat divergence plays a driving role in speciation. Severe environmental fluactuations and/or stress may bring about unreduced gamete formation in germline or mitotic errors in somatic tissues, enabling the establishment of new genomic states. However, fixation of any such variation should involve merchanisms that produce reproductively isolated lineages. This could be realized either through polyploidy enabling alteration in genomic constitution involving chromosome duplication and/or numerical/structural chromome alterations or by hybridization/homoploidy. Whereas polyploidy may lead to stable genomic states owing to their tolerance to post-polyploid genetic modification; the interspecies hybridization is often maladaptive but can also promote speciation through generation of homoploid hybrids (i.e. hybridization without polyploidy) enabling reproductive isolation of evolving hybrids. However, homoploidy as a speciation mechanism is considered only as a minor contributor in evolution, but polyploidy, more particularly autopolyploidy stands apart as a major evolutionary force owing to its wide occurrence and short generation time, and shall continue to be as an effective speciation mechanism to sustain habitat disturbance emanating from rigors of climate change. [ABSTRACT FROM AUTHOR]

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Whole genome duplication leads to autopolyploidy and brings about an increase in cell size, concentration of secondary metabolites and enhanced cytosine methylation. The increased cell size offers a positive advantage to polyploids for cell-surface-related activities, but there is a differential response to change in body size across species and taxonomic groups. Although polyploidy has been very extensively studied, having genetic, ecological and evolutionary implications, there is no report that underscores the significance of native secondary metabolites vis-à-vis body size with ploidy change. To address this problem we targeted unique diploid-autotetraploid paired sets of eight diverse clones of six species of Cymbopogon- a species complex of aromatic grasses that accumulate qualitatively different monoterpene essential oils (secondary metabolite) in their vegetative biomass. Based on the qualitative composition of essential oils and the plant body size relationship between the diploid versus autotetraploid paired sets, we show that polyploidy brings about enhanced accumulation of secondary metabolites in all cases, but exerts differential effects on body size in various species. It is observed that the accumulation of alcohol-type metabolites (e.g. geraniol) does not inhibit increase in body size with ploidy change from 2× to 4× ( r = 0.854, P < 0.01), but aldehyde-type metabolites (e.g. citral) appear to drastically impede body development ( r = −0.895). Such a differential response may be correlated to the metabolic steps involved in the synthesis of essential oil components. When changed to tetraploidy, the progenitor diploids requiring longer metabolic steps in production of their secondary metabolites are stressed, and those having shorter metabolite routes better utilize their resources for growth and vigour. In situ immunodetection of 5-methylcytosine sites reveals enhanced DNA methylation in autopolyploids. It is underpinned that the qualitative composition of secondary metabolites found in the vegetative biomass of the progenitor diploid has a decisive bearing on the body size of the derived autotetraploids and brings about an enhancement in genome-wide cytosine methylation. [ABSTRACT FROM AUTHOR]

In most medicinal and aromatic plants, the vegetative tissue (e.g., roots, stems, leaves) is the source of the economic product. These plants are inherently heterozygous (natural allelic hybrids) and maintain their genetic makeup in nature by obligate vegetative propagation. Under seed cultivation, these plants incur population heterogeneity that reduces biomass and hampers product quality. Therefore, fixation of heterozygosity is vital for maintaining uniformity in quality of the economic product and quantity of biomass under seed cultivation. Although seed-grown clonal progenies identical to the mother plant can be obtained in certain plants that show an unusual breeding system called apomixis, such a breeding system is rare in medicinal and aromatic plants of economic value. Here we show an effective experimental strategy based on a polyploid model that facilitates fixation of heterozygosity in obligate asexual species owing to tetrasomic inheritance and low segregation in C1 progenies from high-fertility C0 autopolyploids. Using an obligate asexual species of aromatic grass—Cymbopogon martinii, we demonstrated that progenitor diploids with distal chiasma localization and low chiasmate association in meiosis, when changed into tetraploids, entail high gametic/seed fertility reflected in high bivalent pairing and balanced anaphase segregation. Their seed progenies evince crop homogeneity owing to reduced segregation, indicating fixation of heterozygosity present in the source diploids. Because C. martinii could be maintained through obligate vegetative propagation, here is a unique opportunity to utilize the polyploid advantage through C1 seed progenies for commercial cultivation, as well as maintenance of original C0 stock for raising seeds without losing polyploid heterosis normally threatened in subsequent segregating progenies on account of aneuploidy and gametic instability. [ABSTRACT FROM PUBLISHER]

The author would like to correct the following error in the publication of the article. [ABSTRACT FROM AUTHOR]