Population Of Var Research Articles

Telomere-to-telomere assembled and centromere annotated genomes of the two main subspecies of the button mushroom Agaricus bisporus reveal especially polymorphic chromosome ends

Agaricus bisporus, the most cultivated edible mushroom worldwide, is represented mainly by the subspecies var. bisporus and var. burnettii. var. bisporus has a secondarily homothallic life cycle with recombination restricted to chromosome ends, while var. burnettii is heterothallic with recombination seemingly equally distributed over the chromosomes. To better understand the relationship between genomic make-up and different lifestyles, we have de novo sequenced a burnettii homokaryon and synchronised gene annotations with updated versions of the published genomes of var. bisporus. The genomes were assembled into telomere-to-telomere chromosomes and a consistent set of gene predictions was generated. The genomes of both subspecies were largely co-linear, and especially the chromosome ends differed in gene model content between the two subspecies. A single large cluster of repeats was found on each chromosome at the same respective position in all strains, harbouring nearly 50% of all repeats and likely representing centromeres. Repeats were all heavily methylated. Finally, a mapping population of var. burnettii confirmed an even distribution of crossovers in meiosis, contrasting the recombination landscape of var. bisporus. The new findings using the exceptionally complete and well annotated genomes of this basidiomycete demonstrate the importance for unravelling genetic components underlying the different life cycles.

Male meiosis in Lotus corniculatus L.

In the present study, male meiosis was investigated in Lotus corniculatus from different geographical areas of the Kashmir Himalayas. The 2n = 4x = 24 in one cytotype of var. minor is reported for the first time worldwide, whereas 2n = 2x = 12 for var. corniculatus, var. japonicus and var. minor are reported for the first time in India. The meiotic course in the three populations of var. minor is highly abnormal as shown by chromatin transfer between different pollen mother cells (PMCs) which is associated with other meiotic abnormalities affecting pollen fertility and pollen size. Further, in the diploid population of var. minor, due to cytomixis, a few PMCs have been observed with a double chromatin mass and two nucleoli at diakinesis as well as almost double the size of normal PMCs. However, the frequency of these PMCs is very low (1.81 %). As a result of cytomixis, such PMCs might have played a role in the production of infraspecific polyploidy in the species.

Essential oils composition in two Rosmarinus officinalis L. varieties and incidence for antimicrobial and antioxidant activities

The essential oil composition of Rosmarinus officinalis var. typicus and var. troglodytorum endemic to Tunisia, and growing wild in different bioclimates, was determined by GC and GC–MS. Oils were assessed for their antimicrobial and antioxidant activity. A variation of the chemical composition attributed to varieties rather than to bioclimates was revealed. 1.8-Cineole (47.2–27.5%) and camphor (12.9–27.9%) were identified as the main constituents of var. typicus and var. troglodytorum, respectively. The principal component analysis performed on oil constituents for all the populations allowed the distinction of two distinct population groups in accordance to the varietal subdivision. Based on the determination of the diameter of inhibition and the determination of the minimum inhibitory concentration, a low to moderate antimicrobial activity according to oils was revealed against eight bacteria tested. However, oils from var. troglodytorum showed higher bactericidal effect than those from var. typicus. The oils’ antioxidant activity, determined by 1,1-diphenyl-1-picrylhydrazyl (DPPH) assay, ferric reducing (FRAP) assay and β-carotene bleaching test, was relatively high. The highest activity was found in oils from var. troglodytorum and in one population of var. typicus from the upper semi-arid bioclimate.

Genetic variability and structure of natural and domesticated populations of Caribbean pine (Pinus caribaea Morelet)

Isozyme analysis of seed samples derived from natural and managed populations of the tropical pine Pinus caribaea vars ‘bahamensis’ and ‘caribaea’ was used to assess population genetic structure in its native range and to detect changes occurring during early domestication of the species. Baseline data from natural populations of the two varieties showed that populations sampled as seed are characterized by high gene diversity (mean He=0.26) and a low level of inbreeding ( mean Fis=0.15). A UPGMA tree of genetic relatedness among populations indicates that the two varieties represent distinct evolutionary units. Within each variety there is significant differentiation among populations, and this is greater for the more fragmented populations of var ‘bahamensis’ (Fst=0.08) than for var ‘caribaea’ (Fst=0.02). Seed from a seed orchard population of var ‘caribaea’ established within its natural range showed no change in genetic diversity but did show a reduced inbreeding coefficient (Fis=0.09) compared with its progenitor populations, suggesting a decrease in selfing and/or biparental inbreeding. A bulked seed sample from an exotic plantation of var ‘bahamensis’ in Australia displayed a large increase in the inbreeding coefficient (Fis=0.324) compared with that found in natural populations, possibly due to elevated self-fertilization. Finally, a bulked seed sample from an exotic plantation population of var ‘caribaea’ from China showed enhanced genetic diversity, an increase in the inbreeding coefficient and more linkage disequilibrium than its presumed progenitor populations. It was also genetically divergent from them. RFLP analysis of chloroplast DNA variation in the Chinese sample suggested that seeds of the related taxa P. elliottii and P. taeda, or seeds derived from hybridization with these taxa growing in the seed production area, had been included in the seed crop during harvesting. We conclude that monitoring of appropriate genetic markers may be an effective means of identifying potentially deleterious genetic changes occurring during forest tree domestication.

Allozyme Divergence and Intraspecific Variation in Coreopsis grandiflora (Compositae)

Coreopsis grandiflora is an herbaceous perennial occurring primarily in the southeast- ern United States. It is morphologically variable and the variation is accommodated in three diploid (var. grandiflora, var. harveyana, var. saxicola) and one hexaploid (var. longipes) varieties. Populations of the three diploid varieties are usually highly interfertile. An electrophoretic study of 14 soluble enzymes presumably coded by 26 genes revealed no differentiation between any of the varieties. Comparable levels of genetic variation were found in populations of each variety and within each variety as a whole. The high genetic identity between the hexaploid var. longipes and the three diploid varieties suggests that the former is an autopolyploid in the sense that its origin lies exclusively within C. grandiflora. All alleles detected in the hexaploid were also found in the diploids, and no fixed heterozygosity was found at any gene in any population of var. longipes. The electrophoretic evidence is concordant with the high morphological similarity between var. longipes and diploid varieties of C. grandiflora in suggesting an autoploid origin for the former.

The cytology of Brachycome

Over 1,000 plants of B. dichromosomatica have been counted. 10% of these carried one, two or three B chromosomes. The B chromosome is large, and though it is not heteropycnotic it condenses precociously at mitosis. It behaves regularly at mitosis, and when two are present they pair regularly at meiosis. Non-disjunction and preferential distribution of the B to the generative nucleus occurs at the first pollen grain mitosis, with very high frequency. This is corroborated by data from crosses, which also indicate that the transmission of the B through the female gamete is normal. — The frequency of B chromosomes in marginal populations of var. dichromosomatica is significantly higher than in central populations. In one population of var. alba the frequency of Bs increased significantly after two very dry seasons. It is suggested that both these cases of increased frequency were in response to a selective advantage of plants with Bs under arid conditions. — Plants with one B chromosome appear to be less fit than plants with 2 Bs. The combination of the calculated effects of the nondisjunction mechanism and the inferred relative fitness of the 0B, 1B and 2B plants, provides a reasonable explanation of the observed frequencies of the 0B, 1B and 2B plants in the populations studied.