Apomixis beyond trees in the Brazilian savanna: new insights from the orchid Zygopetalum mackayi.

n the Neotropics, the focus of apomictic studies predominantly centres on trees within the Brazilian savanna, characterized, mostly as sporophytic and facultative, associated with polyploidy and polyembryony. To enhance our understanding of the mechanisms governing apomixis and sexual reproduction in tropical herbaceous plants, we clarify the relationship between apomixis, chromosome counts, and polyembryony in the epiphytic orchid Zygopetalum mackayi, which forms a polyploid complex within rocky outcrops in both the Brazilian savanna and the Atlantic forest. To define embryo origins and describe megasporogenesis and megagametogenesis, we performed manual self-pollinations in first-day flowers of cultivated plants, considering all three cytotypes (2x, 3x, 4x) of this species. Flowers and fruits at different stages were collected to describe the development and morphology of ovules and seeds considering sexual and apomictic processes. As self-pollination treatments resulted in high fruit abortion in diploids, we also examined pollen tube development in aborted flowers and fruits to search for putative anomalies. Megasporogenesis and megagametogenesis occur regularly in all cytotypes. Apomixis is facultative and sporophytic, and associated with polyploid cytotypes, while diploid individuals exclusively engage in sexual reproduction. Polyembryony is caused mainly by the production of adventitious embryos from nucellar cells of triploids and tetraploids, but also by the development of multiple archesporia in all cytotypes. Like other apomictic angiosperms within the Brazilian savanna, our findings demonstrate that apomixis in Z. mackayi relies on pollinators for seed production. We also consider the ecological implications of these apomictic patterns in Z. mackayi within the context of habitat loss and its dependence on pollinators.

Synthetic Tetraploid of Oncidium crispum Lodd. (Orchidaceae).

In ornamental plants, artificial polyploidization has enabled the creation of new cultivars. Due to their high commercial value in the international flower market and their ornamental characteristics, such as the shape, size, color, and durability of their flower, orchids have received great attention in studies of artificial polyploidization. Here we described the protocol used for polyploid induction in Oncidium crispum, an epiphyte species native of southeastern Brazil, of great ornamental interest and widely sold in flower shops. The species stands out for having inflorescence with large flowers, brown in color with yellow spots. In addition, O. crispum has great potential for use in genetic improvement programs since the species is widely used in interspecific crosses. Closed capsules containing mature O. crispum seeds were subjected to running sterilized water for 10 min and then to a 1.5% sodium hypochlorite solution for 10 min. Small portions of seeds were introduced into 50 mL of water-soluble fertilizer with macro- and micronutrients (B>M) plus 0.7% agar. Explants originating from seeds previously in vitro germinated were submitted to 0.05% and 0.1% of colchicine for 4 days and 8 days. Flow cytometry and chromosome counts confirmed that the protocol successfully produced synthetic polyploid plants.

Growth performance, reproductive status, and chromosomal instability in triploid Nile tilapias.

Reproductive control is one of the biggest challenges in tilapia production and triploidy was developed as an alternative to sterilization. In general, polyploids present chromosomal instability but for triploid Nile tilapia it has yet to be reported. This study evaluated the chromosomal instability from juveniles to adulthood, growth performance and gonadal status of tilapia hatched from eggs submitted or not to heat shock for triploid induction. Nile tilapia oocytes were fertilized (1,476 oocytes), half of the eggs were subjected to a four-minute shock in 41 °C water four minutes after fertilization and the other half were not (Control group). The eggs were incubated (at 27°C) and 160 larvae from the treated group hatched and survived after yolk sac absorption. The determination of ploidy was performed by flow cytometry at 85th (juveniles) and 301st (adults) days of age post yolk sac absorption. At the time of the first cytometry analysis there were 73 surviving juveniles from the treated group, and only 14 were confirmed triploid. However, at the analysis of adult ploidy, one out of 8 surviving adult tilapias from the 14 confirmed triploid juveniles remained triploid. Gonadal histology showed that the non-remaining triploids continued to produce gametes. The growth performance of triploid tilapia was initially superior to that of diploid tilapia during the juvenile phase, but similar in adults. Once the chromosome sets are lost and the tilapias become diploid again, at least in tissues with a high proliferation rate, such as the hematopoietic tissue that was analyzed (and possibly in gonads), all possible advantages of triploids are probably lost. Thus, our results suggest that, due to genomic instabilities, the triploid generation of tilapia has low efficiency.

Phenotypic variation seems not to be associated with the genetic profile in Zygopetalum (Orchidaceae): a case study of a high-elevation rocky complex.

BACKGROUND: Hybridization associated with polyploidy studies is rare in the tropics. The genus Zygopetalum (Orchidaceae) was investigated here as a case study of Neotropical plants. In the rocky highlands of the Ibitipoca State Park (ISP), southeast Brazil, individuals with intermediate colors and forms between the species Z. maculatum and Z. triste were commonly identified. METHODS AND RESULTS: Chromosomal analysis and DNA quantity showed a uniform population. Regardless of the aspects related to the color and shape of floral structures, all individuals showed 2n = 96 chromosomes and an average of 14.05 pg of DNA. Irregularities in meiosis associated with chromosome number and C value suggest the occurrence of polyploidy. The genetic distance estimated using ISSR molecular markers revealed the existence of genetic variability not related to morphological clusters. Morphometric measurements of the flower pieces revealed that Z. maculatum shows higher variation than Z. triste although lacking a defined circumscription. CONCLUSION: The observed variation can be explained by the polyploid and phenotypic plasticity resulting from the interaction of the genotypes with the heterogeneous environments observed in this habitat.

First investigation into the genetic control of meiosis in sugarcane.

The sugarcane (Saccharum spp.) genome is one of the most complex of all. Modern varieties are highly polyploid and aneuploid as a result of hybridization between Saccharum officinarum and S. spontaneum. Little research has been done on meiotic control in polyploid species, with the exception of the wheat Ph1 locus harboring the ZIP4 gene (TaZIP4-B2) which promotes pairing between homologous chromosomes while suppressing crossover between homeologs. In sugarcane, despite its interspecific origin, bivalent association is favored, and multivalents, if any, are resolved at the end of prophase I. Thus, our aim herein was to investigate the purported genetic control of meiosis in the parental species and in sugarcane itself. We investigated the ZIP4 gene and immunolocalized meiotic proteins, namely synaptonemal complex proteins Zyp1 and Asy1. The sugarcane ZIP4 gene is located on chromosome 2 and expressed more abundantly in flowers, a similar profile to that found for TaZIP4-B2. ZIP4 expression is higher in S. spontaneum a neoautopolyploid, with lower expression in S. officinarum, a stable octoploid species. The sugarcane Zip4 protein contains a TPR domain, essential for scaffolding. Its 3D structure was also predicted, and it was found to be very similar to that of TaZIP4-B2, reflecting their functional relatedness. Immunolocalization of the Asy1 and Zyp1 proteins revealed that S. officinarum completes synapsis. However, in S. spontaneum and SP80-3280 (a modern variety), no nuclei with complete synapsis were observed. Importantly, our results have implications for sugarcane cytogenetics, genetic mapping, and genomics.

Polyploid speciation in Zea (Poaceae): cytogenetic insights.

MAIN CONCLUSION: The analysis of meiotic pairing affinities and genomic formulae in species and hybrids of Zea allowed us to speculate an evolutionary model to recreate the ancient polyploidization of maize and allied species. The meiotic pairing affinities and the genomic formulae analysis in Zea species and hybrids obtained in new and previous crosses, together with the molecular data known in the genus, allowed us to speculate an evolutionary model to attempt to recreate the ancient polyploidization process of Zea species. We propose that x = 5 semispecies are the ancestors of all modern species of the genus. The complex evolutionary process that originated the different taxa could be included hybridization between sympatric diploid ancestral semispecies (2n = 10) and recurrent duplication of the hybrid chromosome number, resulting in distinct auto- and allopolyploids. After the merger and doubling of independent genomes would have undergone cytological and genetical diploidization, implying revolutionary changes in genome organization and genic balance processes. Based on the meiotic behaviour of the 2n = 30 hybrids, that showed homoeology between the A subgenomes of all parental species, we propose that this subgenome A would be pivotal in all the species and would have conserved the rDNA sequences and the pairing regulator locus (PrZ). In the hypothetical model postulated here, the ancestral semispecies with the pivotal subgenome A would have had a wide geographic distribution, co-occurring and hybridizing with the semispecies harbouring B subgenomes, thus enabling sympatric speciation.

Nuclear Morphofunctional Organization and Epigenetic Characteristics in Somatic Cells of T. infestans (Klug, 1834).

Triatoma infestans (Klug) is an insect recognized as not only an important vector of South American trypanosomiasis (Chagas disease) but also a model of specific cellular morphofunctional organization and epigenetic characteristics. The purpose of the present review is to highlight certain cellular processes that are particularly unveiled in T. infestans, such as the following: (1) somatic polyploidy involving nuclear and cell fusions that generate giant nuclei; (2) diversification of nuclear phenotypes in the Malpighian tubules during insect development; (3) heterochromatin compartmentalization into large bodies with specific spatial distribution and presumed mobility in the cell nuclei; (4) chromatin remodeling and co-occurrence of necrosis and apoptosis in the Malpighian tubules under stress conditions; (5) epigenetic markers; and (6) response of heterochromatin to valproic acid, an epidrug that inhibits histone deacetylases and induces DNA demethylation in other cell systems. These cellular processes and epigenetic characteristics emphasize the role of T. infestans as an attractive model for cellular research. A limitation of these studies is the availability of insect supply by accredited insectaries. For studies that require the injection of drugs, the operator's dexterity to perform insect manipulation is necessary, especially if young nymphs are used. For studies involving in vitro cultivation of insect organs, the culture medium should be carefully selected to avoid inconsistent results.

Alternative Evolutionary Pathways in Paspalum Involving Allotetraploidy, Sexuality, and Varied Mating Systems.

The genetic systems of Paspalum species have not been extensively studied. We analyzed the ploidy, reproductive mode, mating system, and fertility of four Paspalum species-Paspalum durifolium, Paspalum ionanthum, Paspalum regnellii, and Paspalum urvillei. An analysis of 378 individuals from 20 populations of northeastern Argentina was conducted. All populations of the four Paspalum species were pure tetraploid and had a sexual and stable reproductive mode. However, some populations of P. durifolium and P. ionanthum showed low levels of apospory. Populations of P. durifolium and P. ionanthum had low seed sets under self-pollination but were fertile under open pollination, showing that self-incompatibility likely caused self-sterility. In contrast, populations of P. regnellii or P. urvillei showed no evidence of apospory, and seed sets in both self- and open pollination conditions were high, suggesting that they are self-compatible due to the absence of pollen-pistil molecular incompatibility mechanisms. The evolutionary origin of the four Paspalum species could explain these differences. This study supplies valuable insights into the genetic systems of Paspalum species, which could have implications for their conservation and management.

Reproductive and Agronomic Characterization of Novel Apomictic Hybrids of Paspalum (Poaceae).

The tetraploid germplasm of Paspalum contains a large diversity that can be used to generate better forages. The objective was to evaluate a group of Paspalum notatum and Paspalum simplex apomictic hybrids for a set of agronomic traits and apomixis expressivity. Forage yield, cold tolerance, winter regrowth, and seed yield were evaluated. The expressivity of apomixis was evaluated in P. simplex hybrids by flow cytometry. Progeny testing with molecular markers was used to determine the genotypic variability in the progeny. Differences within P. notatum and P. simplex hybrids were observed for all traits, and some of them were superior in comparison with the controls. The accumulated forage yield during three years was 988 g m-2 in the P. notatum hybrids, whereas, in P. simplex, the average forage yield per harvest (40 days of regrowth) was 180 g m-2. In P. simplex, the apomixis expressivity varied between 0 and 100%, and 65% of the hybrids showed high apomixis expressivity (superior to 70%). The genotypic mean homogeneity in the progeny was 76% and 85% in P. notatum and P. simplex, respectively. The generation of hybrids with high apomixis expressivity that combine good agronomic performance and homogeneity in the offspring is possible in tetraploid P. notatum and P. simplex.

Phylogeography of Eriotheca species complex: insights into the origin and range expansion of apomictic and polyploid trees in Neotropical Savannas.

Polyploidy and whole genome duplication are major evolutionary drivers in plants. Climate variations during the Pleistocene have influenced distribution and range expansion worldwide. Similar trends have been reported for Cerrado plants, but no attempt has been made to link phylogeography with ploidy and breeding changes. Thus, we aimed to (i) assess ploidy and genome size of Eriotheca estevesiae Carv.-Sobr., and compare it with E. pubescens (Mart.) Schott & Endl. (Both included into the Eriotheca Stellate Trichome Species Complex - ESTSC). (ii) Subsequently, we investigated their phylogeography to see whether genetic structure and range expansion trends were similar to those previously described for the Cerrado biome. Finally (iii), we discuss whether ESTSC phylogeographic patterns could be associated with geographic parthenogenesis processes. Common cytogenetic techniques and flow cytometry were used to confirm chromosome number and genome size of E. estevesiae. We used three cpDNA regions to analyse 14 ESTSC Cerrado populations, for which we also obtained ploidy level and breeding information. We investigated haplotype diversity, population structure and tested neutrality, aiming to reconstruct phylogeographic scenarios. We found three ploidy levels and eight cpDNA haplotypes in ESTSC, one shared by most populations. Haplotype and ploidy distribution corroborated that E. pubescens, the widely distributed polyploid and apomictic species, may have originated from northern diploid and probably sexual E. estevesiae. Matrilinear cpDNA links support the idea that apomixis and polyploidy in ESTSC may have allowed range expansion during the Pleistocene, in a process analogous to the geographic parthenogenesis described elsewhere.

Relationship between fruit phenotypes and domestication in hexaploid populations of biribá (Annona mucosa) in Brazilian Amazonia.

Background: Biribá (Annona mucosa Jacq.) is a fruit tree domesticated in Amazonia and has polyploid populations. The species presents ample phenotypic variation in fruit characteristics, including weight (100-4,000 g) and differences in carpel protrusions. Two cytotypes are recorded in the literature (2n = 28, 42) and genome size records are divergent (2C = 4.77, 5.42 and 6.00 pg). To decipher the role of polyploidy in the domestication of A. mucosa, we examined the relationships among phenotypic variation, chromosome number and genome size, and which came first, polyploidization or domestication. Methodology: We performed chromosome counts of A. mucosa from central and western Brazilian Amazonia, and estimated genome size by flow cytometry. We performed phylogenetic reconstruction with publicly available data using a Bayesian framework, time divergence analysis and reconstructed the ancestral chromosome number for the genus Annona and for A. mucosa. Results: We observed that variation in fruit phenotypes is not associated with variation in chromosome number and genome size. The most recent common ancestor of A. mucosa is inferred to be polyploid and diverged before domestication. Conclusions: We conclude that, when domesticated, A. mucosa was already polyploid and we suggest that human selection is the main evolutionary force behind fruit size and fruit morphological variation in Annona mucosa.

Cytogenetics of Chilean land plants (Embryophyta): state-of-the-art and prospects / CItogenética de plantas terrestres Chilenas (Embryophyta): estado del arte y perspectivas

ABSTRACT Chile is located in the south-western region of South America along the Pacific Ocean and contributes to the worldwide flora with ca. 6,120 species of Bryophyta, Pteridophyta, Pinophyta, Gnetophyta, and Magnoliophyta (1.9% of worldwide total species), exhibiting high endemism across all plant divisions. Little is known about the genetic diversity of Chilean land plants worldwide, including their cytogenetic and molecular characteristics. In 2012 we published the first state-of-the-art review in Cytogenetics of Chilean Angiosperms. The article gathered 78 publications from 1924 to 2010 accounting for approximately 139 species (2.8% of total Chilean species). The aim of this paper was to review the advances in cytogenetic studies of Chilean land plants, reporting additional cytogenetic data for species of four botanical divisions until 2020. Cytogenetic data were searched in the CPCD (Chilean Plants Cytogenetic Database). In total, we found 180 publications from both Chilean and foreign researchers. To date, cytogenetic data have been reported for 499 Chilean land plant species (8.2% of total) belonging to 244 genera and 117 families. In this context, the 2001-2020 period has been among the most productive regarding publications, with 74 available reports that include 163 additional species. Based on chromosome numbers, angiosperms and bryophytes registered the greatest diversity with 55 and 29 different 2n, respectively; both divisions having the greatest number of studied species. Given the importance of increasing information on Chilean land plants, it is expected that more publications will contribute to the knowledge of their cytogenetic diversity in the near future.

RESUMEN Chile está ubicado en la región suroeste de América del Sur a lo largo del Océano Pacífico y contribuye a la flora mundial con aproximadamente 6.120 especies de Bryophyta, Pteridophyta, Pinophyta, Gnetophyta y Magnoliophyta (1,9% del total de especies en todo el mundo), que presentan un alto endemismo en todas las divisiones de plantas. Poco se conoce sobre la diversidad genética de las plantas terrestres chilenas en todo el mundo, incluidas sus características citogenéticas y moleculares. En 2012 publicamos la primera revisión sobre el estado del arte en Citogenética de Angiospermas Chilenas. El artículo reunió 78 publicaciones desde 1924 hasta 2010, que representan aproximadamente 139 especies (2,8% del total de especies chilenas). El objetivo de este trabajo fue revisar los avances en estudios citogenéticos de plantas terrestres chilenas, reportando datos citogenéticos adicionales para especies de cuatro divisiones botánicas hasta el 2020. Los datos citogenéticos se buscaron en el CPCD (Base de Datos Citogenéticos de Plantas Chilenas). En total, encontramos 180 publicaciones sobre citogenética de plantas terrestres chilenas, con datos citogenéticos para 499 especies (8,2% del total) pertenecientes a 244 géneros y 117 familias. En este contexto, el período 2001-2020 ha sido uno de los más productivos en cuanto a publicaciones, con 74 artículos disponibles que incluyen 163 especies adicionales. Basado en los números cromosómicos, angiospermas y briófitos registran la mayor diversidad, con 55 y 29 2n diferentes, respectivamente; ambas divisiones tienen también el mayor número de especies estudiadas. Dada la importancia de incrementar la información sobre plantas terrestres chilenas, se espera que más publicaciones contribuyan al conocimiento de su diversidad citogenética en un futuro próximo.

Evolutionary dynamics of autopolyploids in natural populations: the case of Turnera sidoides complex / Dinámica evolutiva de autopoliploides en poblaciones naturales: el caso del complejo Turnera sidoides

ABSTRACT Turnera sidoides (x=7) is one of the few well-studied South American autopolyploid complexes. Since polyploidy has played a prominent role within this complex, ongoing studies in T. sidoides focus on understanding the mechanisms involved in the origin and the establishment of polyploids using integrative approaches. This paper synthesises the results of more than 20 years of research on this topic. Cytogenetics analysis provided evidences for the production of unreduced male and female gametes, supporting the hypothesis of bilateral sexual polyploidization as the mechanism of origin of polyploids in T. sidoides. The finding of viable triploids suggested that unilateral sexual polyploidization could also be an important mechanism for the origin of tetraploids in T. sidoides. The occurrence of plants continuously forming many unreduced gametes would play a key role in the establishment of neopolyploids in natural populations. Also, the higher number of propagules that tetraploids contribute to subsequent generations, the ability to multiply asexually by rhizomes, and the occurrence of occasional cases of self-compatibility and successful illegitimate crosses in polyploids increase the likelihood that a low frequency of neopolyploids can be maintained in natural populations of T. sidoides. In addition, integration of cytogeographic and genetic divergence data together with past niche modelling provided further insights supporting the hypothesis that historical climatic and geomorphological events provided favourable conditions for the establishment of autopolyploids, with the wider distribution of tetraploids of T. sidoides being the result of their range expansion.

RESUMEN Turnera sidoides (x=7) es uno de los pocos complejos autopoliploides sudamericanos bien estudiados. Como la poliploidía ha tenido un papel destacado en el complejo, los estudios en curso en T. sidoides se centraron en la comprensión de los mecanismos implicados en el origen y el establecimiento de los poliploides mediante diferentes enfoques. En este trabajo se sintetizan los resultados de más de 20 años de investigación sobre este tema. El análisis citogenético proporcionó evidencias de la producción de gametos masculinos y femeninos no reducidos, sustentando la hipótesis de la poliploidización sexual bilateral como mecanismo de origen de los poliploides en T. sidoides. Sin embargo, el hallazgo de triploides fértiles sugirió que la poliploidización sexual unilateral también sería un mecanismo importante de origen de tetraploides en T. sidoides. La ocurrencia de plantas que forman continuamente gametos no reducidos desempeñaría un papel clave en el establecimiento de neopoliploides. Además, el mayor número de propágulos que los tetraploides aportan a las siguientes generaciones, la capacidad de multiplicación asexual por rizomas y los casos ocasionales de autocompatibilidad y cruzamientos ilegítimos exitosos aumentarían la probabilidad de que se mantenga una baja frecuencia de neopoliploides en las poblaciones naturales de T. sidoides. Asimismo, la integración de datos citogeográficos y de divergencia genética junto con el modelado de nicho en el pasado aportó información que sustenta la hipótesis de que los eventos climáticos y geomorfológicos históricos proporcionaron las condiciones favorables para el establecimiento y expansión de los tetraploides de T. sidoides.

Variation of Residual Sexuality Rates along Reproductive Development in Apomictic Tetraploids of Paspalum.

Most apomictic plants are facultative, maintaining the ability to reproduce sexually at different frequencies depending on the taxa, ploidy, and reproductive stage. In this context, Paspalum species are good model systems for studies evaluating the varying levels of apomixis expression. We aimed to identify, in apomictic tetraploid Paspalum species, the degree of apomixis and residual sexuality in three stages of reproductive development, and if their expression varies along them in order to predict their realized impact on the genetic diversity of future generations. Three main stages in the reproductive development (i.e., ovule, seed, and progeny) were studied in tetraploids from populations of P. cromyorhizon and P. maculosum. Mature ovules were studied using cytoembryological analysis, seeds by flow cytometry, and progeny tests with molecular markers. The expression of sexuality and apomixis was compared in each stage. We observed a decline in expression of sexual reproduction through the consecutive stages, jointly with an increase of apomixis expression. Both species showed at least one tetraploid plant capable of producing progeny by sexual means. These small rates of sexually originated progeny prove the ability of apomictic plants to produce low levels of genetic variation through rare events of sexuality. This study also demonstrates the importance of analyzing different reproductive stages in order to get a whole picture of the reproductive outcomes in plant evolution.

Advances and Perspectives for Polyploidy Breeding in Orchids.

The orchid market is a dynamic horticultural business in which novelty and beauty command high prices. The two main interests are the development of flowers, from the miniature to the large and showy, and their fragrance. Overall organ size might be modified by doubling the chromosome number, which can be accomplished by careful study of meiotic chromosome disjunction in hybrids or species. Meiosis is the process in which diploid (2n) pollen mother cells recombine their DNA sequences and then undergo two rounds of division to give rise to four haploid (n) cells. Thus, by interfering in chromosome segregation, one can induce the development of diploid recombinant cells, called unreduced gametes. These unreduced gametes may be used for breeding polyploid progenies with enhanced fertility and large flower size. This review provides an overview of developments in orchid polyploidy breeding placed in the large context of meiotic chromosome segregation in the model plants Arabidopsis thaliana and Brassica napus to facilitate molecular translational research and horticultural innovation.

Coffea cytogenetics: from the first karyotypes to the meeting with genomics.

MAIN CONCLUSION: Coffea karyotype organization and evolution has been uncovered by classical cytogenetics and cytogenomics. We revisit these discoveries and present new karyotype data. Coffea possesses ~ 124 species, including C. arabica and C. canephora responsible for commercial coffee production. We reviewed the Coffea cytogenetics, from the first chromosome counting, encompassing the karyotype characterization, chromosome DNA content, and mapping of chromosome portions and DNA sequences, until the integration with genomics. We also showed new data about Coffea karyotype. The 2n chromosome number evidenced the diploidy of almost all Coffea, and the C. arabica tetraploidy, as well as the polyploidy of other hybrids. Since then, other genomic similarities and divergences among the Coffea have been shown by karyotype morphology, nuclear and chromosomal C-value, AT and GC rich chromosome portions, and repetitive sequence and gene mapping. These cytogenomic data allowed us to know and understand the phylogenetic relations in Coffea, as well as their ploidy level and genomic origin, highlighting the relatively recent allopolyploidy. In addition to the euploidy, the role of the mobile elements in Coffea diversification is increasingly more evident, and the comparative analysis of their structure and distribution on the genome of different species is in the spotlight for future research. An integrative look at all these data is fundamental for a deeper understanding of Coffea karyotype evolution, including the key role of polyploidy in C. arabica origin. The 'Híbrido de Timor', a recent natural allotriploid, is also in the spotlight for its potential as a source of resistance genes and model for plant polyploidy research. Considering this, we also present some unprecedented results about the exciting evolutionary history of these polyploid Coffea.

Polyploidization in Orchids: From Cellular Changes to Breeding Applications.

Polyploidy occurs naturally in plants through cell division errors or can artificially be induced by antimitotic agents and has ecological effects on species adaptation, evolution, and development. In agriculture, polyploidy provides economically improved cultivars. Furthermore, the artificial induction of polyploids increases the frequency; thus, it accelerates obtaining polyploid plants used in breeding programs. This is the reason for its use in developing many crops of economic interest, as is the case of orchids in the flower market. Polyploidy in ornamental plants is mainly associated with flowers of larger size, fragrance, and more intense coloring when compared to naturally diploid plants. Currently, orchids represent the largest flower market worldwide; thus, breeding programs aim to obtain flowers with the larger size, durability, intense colors, and resistance to pathogens. Furthermore, orchid hybridization with polyploidy induction has been used to produce improved hybrid cultivars. Thus, the objective of this review was to compile information regarding the natural occurrence, importance, and methods of induction of polyploidy in orchids. The study also summarizes the significance of polyploids and techniques associated with artificially inducing polyploidy in different orchids of commercial relevance.

Higher frequency of legitimate pollinators and fruit set of autotetraploid trees of Libidibia ferrea (Leguminosae) compared to diploids in a mixed tropical urban population.

In mixed-ploidy populations, newly formed polyploids initially occur at low frequencies when compared to diploids. However, polyploidy may lead to morphological and phenological changes, which promote reproductive isolation and favor polyploid establishment and reproductive success. Additionally, previous studies have shown that polyploidy can confer some adaptive advantages to organisms in stressful environments. Here, we investigate variation in reproductive phenology, floral traits and reproductive success between diploid and autotetraploid trees of Libidibia ferrea (Mart. Ex Tul.) L.P. Queiroz (Leguminosae) in a mixed tropical urban population, a stressful environment. We assessed ploidy levels, flowering and fruiting phenology, flowering synchrony, floral and reproductive biology, pollination and fruit and seed set. We tested the hypothesis that autotetraploid individuals have a higher frequency of pollinators and higher fruit and seed set per inflorescence (as a proxy of reproductive success) than diploids in an urban green space. Libidibia ferrea is a good model to test our hypothesis because it is self-incompatible (i.e. relies on pollinators to set fruits). In the urban ecosystem studied, we found that diploids flowered for 6-7 months/year and autotetraploids for 3-5 months/year. Flowering synchrony was low between and within cytotypes and even though autotetraploids and diploids exhibited some overlap in flowering period, diploids flowered alone for 2-3 months. Autotetraploids had significantly more flowers per inflorescences, larger flowers and larger pollen grains (as expected for polyploids), but also a higher frequency of visits by legitimate pollinators including two exclusive ones, and higher fruit and seed set per inflorescence when compared to diploids, despite having a shorter flowering period. Our findings reveal some advantages for polyploids over their related diploids in a tropical urban green space. Also, our results highlight the need for more studies that seek to understand abiotic mechanisms affecting reproductive output of polyploids in urban ecosystems.

Are chromosome number and genome size associated with habit and environmental niche variables? Insights from the Neotropical orchids.

BACKGROUND AND AIMS: The entangled relationship of chromosome number and genome size with species distribution has been the subject of study for almost a century, but remains an open question due to previous ecological and phylogenetic knowledge constraints. To better address this subject, we used the clade Maxillariinae, a widely distributed and karyotypically known orchid group, as a model system to infer such relationships in a robust methodological framework. METHODS: Based on the literature and new data, we gathered the chromosome number and genome size for 93 and 64 species, respectively. We built a phylogenetic hypothesis and assessed the best macroevolutionary model for both genomic traits. Additionally, we collected together ecological data (preferences for bioclimatic variables, elevation and habit) used as explanatory variables in multivariate phylogenetic models explaining genomic traits. Finally, the impact of polyploidy was estimated by running the analyses with and without polyploids in the sample. KEY RESULTS: The association between genomic and ecological data varied depending on whether polyploids were considered or not. Without polyploids, chromosome number failed to present consistent associations with ecological variables. With polyploids, there was a tendency to waive epiphytism and colonize new habitats outside humid forests. The genome size showed association with ecological variables: without polyploids, genome increase was associated with flexible habits, with higher elevation and with drier summers; with polyploids, genome size increase was associated with colonizing drier environments. CONCLUSIONS: The chromosome number and genome size variations, essential but neglected traits in the ecological niche, are shaped in the Maxillariinae by both neutral and adaptive evolution. Both genomic traits are partially correlated to bioclimatic variables and elevation, even when controlling for phylogenetic constraints. While polyploidy was associated with shifts in the environmental niche, the genome size emerges as a central trait in orchid evolution by the association between small genome size and epiphytism, a key innovation to Neotropical orchid diversification.

Diversity, phylogeny and evolution of the rapidly evolving genus Psidium L. (Myrtaceae, Myrteae).

BACKGROUND AND AIMS: Psidium is the fourthth largest genus of Myrtaceae in the Neotropics. Psidium guajava is widely cultivated in the tropics for its edible fruit. It is commercially under threat due to the disease guava decline. Psidium cattleyanum is one of the 100 most invasive organisms in the world. Knowledge of the phylogenetic relationships within Psidium is poor. We aim to provide a review of the biology, morphology and ecology of Psidium, a phylogenetic tree, an infrageneric classification and a list of species. METHODS: Morphological and geographic data were obtained by studying Psidium in herbaria and in the field between 1988 and 2020. Forty-six herbaria were visited personally. A database of approx. 6000 specimens was constructed, and the literature was reviewed. Thirty species (about a third of the species in the genus) were sampled for molecular phylogenetic inference. Two chloroplast (psbA-trnH and ndhF) and two nuclear (external transcribed spacer and internal transcribed spacer) regions were targeted. Phylogenetic trees were constructed using maximum likelihood (ML; RaxML) and Bayesian inference (BI; MrBayes). KEY RESULTS: Psidium is a monophyletic genus with four major clades recognized as sections. Section Psidium (ten species), to which P. guajava belongs, is sister to the rest of the genus; it is widespread across the Neotropics. Section Obversifolia (six species; restricted to the Brazilian Atlantic Forest), which includes P. cattleyanum, is sister to the innermost clade composed of sister sections Apertiflora (31 species; widespread but most diverse in the Brazilian Atlantic Forest) + Mitranthes (26 species; widespread in dry forests and probably diverse in the Caribbean). Characters associated with diversification within Psidium are discussed. CONCLUSIONS: Research on pre-foliation, colleters, leaf anatomy, leaf physiology, staminal development, placentation and germination associated with the anatomy of the opercular plug is desirable. Studies are biased towards sections Psidium and Obversifolia, with other sections poorly known.