High pollen sterility and 2n pollen grains in an asynaptic 4x cytotype (2n=48) of Solanum nigrum L.

摘要

Cytological investigations have been carried out on the 9 wild accessions of Solanum nigrum L., a medicinally important species having wide-range therapeutic properties. Male meiotic studies performed in 9 accessions revealed the presence of 3 intraspecific cytotypes, 2x (n=12), 4x (n=24) and 6x (n=36) in the species. The course of meiosis in 8 of the 9 accessions among the 2x, 4x, 6x cytotypes was noticed to be perfectly normal resulting in very high pollen fertility (95-100%). However, 1 accession of 4x cytotype scored from Palchan (Solang Valley, Kullu, Himachal Pradesh) depicted irregular chromosomal behaviour during meiosis due to the presence of all 48 chromosomes as univalents. The further course of meiosis in this individual was highly irregular with the presence of large number of lagging and unoriented chromosomes, eccentric positioned univalents in the PMCs and unequal distribution of chromosomes at anaphase-I. Microsporogenesis was also abnormal which is characterized by the presence of irregular sporads, such as dyads, triads and polyads. Lagging chromosomes constituted micronuclei at sporad stages. Consequent to all these meiotic irregularities, 95% of the pollen grains were observed to be sterile. Pollen grains were also recorded to be of different sizes. In meiotically abnormal 4x accession, pollen grains were of 2 different types compared to normal 4x plants showing perfectly normal meiosis. The large pollen grains, which were measured to be 1.25-1.5 times bigger than normal sized pollen grains, were considered as unreduced or 2n pollen grains. The role of such 2n (unreduced) pollen grains in producing polyploid genotypes through sexual polyploidization in a chromosomally variable S. nigrum (2x, 3x, 4x, 5x, 6x, 8x, 9x, 12x) has also been discussed.