Cytological Studies of Some Dicots from the Hills of Mandi District (Himachal Pradesh) in Northwest Indian Himalayas

Details of male meiotic course and pollen fertility have been investigated in 45 species of dicotyledonous plants from the chromosomally unexplored area of the Mandi district, between the attitudinal ranges of 800 to 3360m. All the species have been worked out cytologically for the first time from the study area. The meiotic chromosome count of n=9 for Impatiens micranthemum is the first ever chromosome report for the species. A new intraspecific 12x cytotype (n=42) has been reported in Potentilla gerardiana, supplementing the earlier reported cytotypes (2x, 8x). A new cytotype has been reported in Gentiana argentea (n=9), supplementing the earlier Indian report of n=10. Out of a total 45 species, 31 species (68.89%) showed normal meiotic course and high pollen fertility (91-100%), while 14 species (31.11%) depicted various meiotic irregularities and some pollen sterility (4-40%). The phenomenon of cytomixis involving inter-pollen mother cells (PMCs) migration of chromatin material has been reported in 3 species, Clematis grata (n=8), Gentiana aprica (n=10) and Lamium album (n=9). In these species, cytomixis induces various meiotic abnormalities (enucleated, hypo-, hyperploid, tripolar and multipolar PMCs, chromatin stickiness, laggards and chromatin bridges at anaphases and telophases and micronuclei) and consequently some pollen sterility and variable sized pollen grains. Besides, non-synchronous disjunctions of bivalents at anaphases, abnormal spindles, and interbivalent connections during diakinesishnetaphase-I, univalents and multivalents have also been reported in certain cases. The chromosome counts in the remainder of the species substantiate previous counts by other researchers.