Chromosome constitution of some Indian tea clones

Resultant of large-scale spontaneous hybridization between Camellia taxa, the present day commercial tea clones are highly variable and heterozygous. It is in this context that thirty two UPASl and other tea clones were investigated with regard to comparative karyomorphology and meiotic pairing properties so as to ascertain the nature and extent of intra - and interclonal differentiation. Barring one clone (UPASI 3), all other investigated clones were diploid (2n = 2x = 30) in constitution. UPASl3 was triploid (2n = 3x = 45) in constitution. The chromosome complements in the diploid tea clones, wherever investigated, resolved into 15 median and submedian homomorphic pairs. Between clones, minor variation in the proportion of median and submedian chromosomes and (or) number and location of secondary constrictions was observed. lnspite of the fact that tea clones are considered to be highly heterozygous, the male meiosis in the diploid clones was perfectly normal resulting in regular 15 bivalents at diakinesislmetaphase I, and equal (1 5:15) distribution of chromosomes at anaphase I. The only feature which could indicate degree of cryptic hybridity was the occurrence of bivalents with localized chiasmata. The predominant occurrence of trivalents in the triploid UPASI 3 indicated either autopolyploid or segmental allopolyploid origin. The genomic constitution of tea clones is discussed in the light of present results.This item was scanned with a HP 4850 Scanjet at 300 dpi and consists of 8 pages

Allium cytogenetics: a critical review on the Indian taxa

The genus Allium Linnaeus, 1753 (tribe Allieae) contains about 800 species worldwide of which almost 38 species are reported in India, including the globally important crops (onion, garlic, leek, shallot) and many wild species. A satisfactory chromosomal catalogue of Allium species is missing which has been considered in the review for the species occurring in India. The most prominent base number is x=8, with few records of x=7, 10, 11. The genome size has sufficient clues for divergence, ranging from 7.8 pg/1C to 30.0 pg/1C in diploid and 15.16 pg/1C to 41.78 pg/1C in polyploid species. Although the karyotypes are seemingly dominated by metacentrics, substantial variation in nucleolus organizing regions (NORs) is noteworthy. The chromosomal rearrangement between A. cepa Linnaeus, 1753 and its allied species has paved way to appreciate genomic evolution within Allium. The presence of a unique telomere sequence and its conservation in Allium sets this genus apart from all other Amaryllids and supports monophyletic origin. Any cytogenetic investigation regarding NOR variability, telomere sequence and genome size in the Indian species becomes the most promising field to decipher chromosome evolution against the background of species diversity and evolution, especially in the Indian subcontinent