Descending Dysploidy and Bidirectional Changes in Genome Size Accompanied Crepis (Asteraceae) Evolution

The evolution of the karyotype and genome size was examined in species of Crepis sensu lato. The phylogenetic relationships, inferred from the plastid and nrITS DNA sequences, were used as a framework to infer the patterns of karyotype evolution. Five different base chromosome numbers (x = 3, 4, 5, 6, and 11) were observed. A phylogenetic analysis of the evolution of the chromosome numbers allowed the inference of x = 6 as the ancestral state and the descending dysploidy as the major direction of the chromosome base number evolution. The derived base chromosome numbers (x = 5, 4, and 3) were found to have originated independently and recurrently in the different lineages of the genus. A few independent events of increases in karyotype asymmetry were inferred to have accompanied the karyotype evolution in Crepis. The genome sizes of 33 Crepis species differed seven-fold and the ancestral genome size was reconstructed to be 1 C = 3.44 pg. Both decreases and increases in the genome size were inferred to have occurred within and between the lineages. The data suggest that, in addition to dysploidy, the amplification/elimination of various repetitive DNAs was likely involved in the genome and taxa differentiation in the genus.

Karyotype asymmetry in Cuscuta L. subgenus Pachystigma reflects its repeat DNA composition

Cuscuta is a cytogenetically diverse genus, with karyotypes varying 18-fold in chromosome number and 89-fold in genome size. Each of its four subgenera also presents particular chromosomal features, such as bimodal karyotypes in Pachystigma. We used low coverage sequencing of the Cuscuta nitida genome (subgenus Pachystigma), as well as chromosome banding and molecular cytogenetics of three subgenus representatives, to understand the origin of bimodal karyotypes. All three species, C. nitida, C. africana (2n = 28) and C. angulata (2n = 30), showed heterochromatic bands mainly in the largest chromosome pairs. Eighteen satellite DNAs were identified in C. nitida genome, two showing similarity to mobile elements. The most abundant were present at the largest pairs, as well as the highly abundant ribosomal DNAs. The most abundant Ty1/Copia and Ty3/Gypsy elements were also highly enriched in the largest pairs, except for the Ty3/Gypsy CRM, which also labelled the pericentromeric regions of the smallest chromosomes. This accumulation of repetitive DNA in the larger pairs indicates that these sequences are largely responsible for the formation of bimodal karyotypes in the subgenus Pachystigma. The repetitive DNA fraction is directly linked to karyotype evolution in Cuscuta.

Orcein and DAPI-stained karyotype analysis of Alocasia macrorrhizos (L.) G. Don

Karyotype analyses are required for the identification, characterization, and genetic improvement of any organism. Alocasia macrorrhizos (L.) G. Don. was investigated cytogenetically to determine the karyotypic features. Complex chromocenter type, of interphase nuclei, and gradient type of prophase chromosomes were found in this study. Alocasia macrorrhizos was found to possesses 2n=28 chromosomes. The total length of the 2n chromosome complement was recorded as 98.83±1.39 μm. The range of chromosomal length was 2.50±0.10-4.70±0.10 μm. A gradual decrease in chromosomal length was observed. The total form (TF%) value was found to be 43.58%, Karyotype symmetry index (Syi %) was 77.00 % and karyotype asymmetry index (AsK %) was 56.66%. The centromeric formula was 18m+4sm+2ac, representing asymmetric karyotype. In DAPI banding, the 1.48% positive banded region indicates the lower amount of AT rich repeats in this material. Therefore, Alocasia macrorrhizos could be authentically characterized through karyotype analysis. J. Bangladesh Acad. Sci. 45(1); 27-35: June 2021

Comparative karyomorphological analysis of two varieties of Brassica campestris from Bangladesh

Two varieties of the oilseed plant viz. Brassica campestris var. Tori-7 and Brassica campestris var. BARI Sarisha-9 were karyomorphologically investigated following orcein staining. Presence of “Round Pro-chromosome Type” of interphase nuclei and “Continuous Type” of prophase chromosomes indicating that both Tori-7 and BARI Sarisha-9 were originated from common ancestor. Moreover, both the varieties were found to possess 2n=20 chromosomes with almost similar range of length i.e.; 0.90±0.04-2.51±0.05μm for Tori-7 and 0.99±0.06-2.60±0.06μm for BARI Sharisha-9. The total length of 2n chromosome complement was recorded as 29.61±0.76μm for Tori-7 and 29.75±0.80μm for BARI Sharisha- 9 where a slight gradual decrease of chromosomal length was observed in both cases. Average chromosomal length, range of individual chromosomal length, relative length and centromeric index of both varieties were more or less similar. Karyotype symmetry index and Karyotype asymmetry index indicating the symmetric nature of both varieties. All metacentric chromosomes were found in Tori-7 representing strictly symmetric karyotype. Beside metacentric, 2 sub-metacentric chromosomes were found in BARI Sharisha-9 representing almost symmetric karyotype. Thus the two varieties of Brassica campestris -were plants of primitive nature. However, BARI Sharisha-9 can be considered comparatively advanced than Tori-7 based on different cytogenetical features. Therefore, the compilation of these karyomorphological information will be useful for authentic identification and characterization of the two varieties of Brassica campestris which are very basic and important information for breeding in crop improvement programme. Jahangirnagar University J. Biol. Sci. 9(1 & 2): 69-77, 2020 (June & December)

Distribution of FISH oligo-5S rDNA and oligo-(AGGGTTT)3 in Hibiscus mutabilis L.

Hibiscus exhibits high variation in chromosome number both within and among species. The Hibiscus mutabilis L. karyotype was analyzed in detail using fluorescence in situ hybridization (FISH) with oligonucleotide probes for (AG3T3)3 and 5S rDNA, which were tested here for the first time. In total, 90 chromosomes were counted in prometaphase and metaphase, and all exhibited similarly intense (AG3T3)3 signals at both ends. (AG3T3)3 showed little variation and thus did not allow discrimination among H. mutabilis chromosomes, but its location at both ends confirmed the integrity of each chromosome, thus contributing to accurate counting of the numerous, small chromosomes. Oligo-5S rDNA marked the proximal/distal regions of six chromosomes: weak signals on chromosomes 7 and 8, slightly stronger signals on chromosomes 15 and 16, and very strong signals on chromosomes 17 and 18. Therefore, 5S rDNA could assist in chromosome identification in H. mutabilis. Metaphase chromosome lengths ranged from 3.00 to 1.18 μm, indicating small chromosomes. The ratios of longest to shortest chromosome length in prometaphase and metaphase were 2.58 and 2.54, respectively, indicating karyotype asymmetry in H. mutabilis. These results provide an exact chromosome number and a physical map, which will be useful for genome assembly and contribute to molecular cytogenetics in the genus Hibiscus.

Genetic Diversity Analysis of Tomato (Solanum lycopersicum L.) with Morphological, Cytological, and Molecular Markers under Heat Stress

Tomatoes are usually consumed daily in the human diet. High temperatures reduce the number of tomato yields per year. Heat stress has been considered one of the most prominent causes of alterations in morphological and molecular characteristics in crops that decrease normal growth, production, and yield in diverse plants, including tomatoes (Solanum lycopersicum L.). In this study, we evaluated six tomato lines, namely G1, G2, G3, G4, G5, and G6, at morphological, molecular, and cytological levels under heat stress. The average results of two seasons (2018 and 2019) clarified that the G6, G1, and G2 lines recorded the highest flowering values, as well as some fruit and vegetative growth traits. Furthermore, G6 and G2 had the maximum number of fruits/plant, whereas G2 and G1 produced the highest yield/plant under high temperatures. The number of chromosomes in all lines was 2n = 24, except for G5, in which the number was 2n = 26, whereas chromosome sizes were small, ranging from 323.08 to 464.48 µm. The G1 cultivar was a symmetrical cultivar (primitive), having the highest total form percentage (TF%) and symmetry index (Syi) values and the minimum karyotype asymmetry index (ASK) value, whereas G4 was asymmetrical (advanced). Molecular marker analysis demonstrated that intersimple sequence repeat (ISSR) primers 49A, HB-14, 49A, 49B, and 89B presented the highest values for polymorphism percentage P%, marker index (MI), effective multiplex ratio (EMR), and polymorphism information content (PIC), respectively. In contrast, OP-A3, OP-B3, SCoT 2, and SCoT 12 primers showed the highest PIC, EMR, MI, P%, and resolving power (Rp) values across the studied random amplified polymorphic DNA (RAPD) and start codon-targeted (SCoT) primers. Moreover, ISSR revealed the highest number of unique specific markers (6), followed by RAPD (4) and SCoT (3) markers. Cluster analysis of combined cytological data and data relating to molecular marker attributes separated the G1, G2, and G3 lines into one group, whereas the other lines were clustered in another group. On the whole, the application of combined analysis using morphological, cytological, and molecular genetics techniques could be considered to provide suitable parameters for studying the evolution of the genetic divergence between the studied tomato lines.

COMPARATIVE KARYOMORPHOLOGICAL STUDIES OF TWO SPECIES OF CRINUM

Crinum asiaticum L. and Crinum latifolium L. are members of the family Amaryllidaceae. Karyomorphological studies of these two species had been performed by using different quantitative and qualitative parameters to know the karyotype asymmetry, which defines the advanced and primitive nature of these two species. The study revealed that Crinum asiaticum L. and Crinum latifolium L. are diploid with 2n=22 chromosomes. based on Total Chromatin Length, Arm Ratio, Gradient Index, Form Percentage, Total Form Percentage, Karyotype Asymmetry Index, Symmetry Index, and Stebbins classification, Crinum asiaticum L. is more advanced than Crinum latifolium L.

Karyotypes and genome size of Adonis amurensis and Adonis apennina (Ranunculaceae) from Asian Russia

The karyotypes of Adonis amurensis from Amur Oblast,' and Adonis apennina from Altai Republic, Khakassia Republic, and Irkutsk Oblast' have been investigated. The karyotype formula was obtained as 2n = 2x =16 = 8m + 8sm(4sat) for all specimens. We estimated karyotype asymmetry through the calculation of the Coefficient of Variation of Chromosome Length (CVCL), Coefficient of Variation of Centromeric Index (CVCI), and Mean Centromeric Asymmetry (MCA), and determination of Stebbins asymmetry index. The chromosome set of Adonis amurensis was found to be more symmetrical than the chromosome set of Adonis apennina. The average absolute nuclear DNA content (2C–value) was originally determined for Adonis amurensis and Adonis apennina by flow cytometry and attained on average 20.38 pg and 17.29 pg, respectively.

Cytogenetic Diversity and Characterization of Vicia sativa Subspecies

Background: Vicia sativa L. is variable genus comprised of several subspecies. Close relative species and subspecies of the cultivated species are easily usable gene sources because they have gained resistance against a wide range of biotic and abiotic stresses. The main objectives of this study are to identify and describe the cytogenetical and karyological characteristics of subspecies in the Vicia sativa complex.Methods: The research material consisted of multiple entries collected from the five subspecies of nine taxa. All cytological observations made from root tips. Six chromosomal parameters (chromosome length, relative length, long arm length, short arm length, arm ratio and centromeric index) and five karyotype asymmetric parameters (difference in relative length, total form percentage, intrachromosomal asymmetry index, interchromosomal asymmetry index and mean centromeric asymmetry) were determined.Result: It was determined that the chromosome number of subspecies were 2n =10-12. The haploid chromosome lengths of subspecies were 15.86-33.88 µm and the average chromosome lengths varied between 2.64-5.65 µm. According to the intrachromosomal karyotype asymmetry index analysis, subsp. segetalis was the most asymmetric karyotype and subsp. sativa “Antalya” was the most symmetric karyotype. According to the interchromosomal karyotype asymmetry index analysis, subsp. angustifolia was the most asymmetric karyotype and subsp. nigra was the most symmetric karyotype.