Secondary chromosome associations and cytomixis in corchorus spp.

Abstract

Meiotic chromosome behavior (bivalent configurations at diplotene, metaphase I chromosome associations and anaphase I chromosome segregations) including secondary chromosome associations and cytomixis were studied in 2 cultivated (Corchorus capsularis L. and C. olitorius L.) and 6 wild (C. aestuans L., C. fascicularis Lamk., C. pseudocapsularis L., C. pseudoolitorius I. and Z., C. tridens L. and C. trilocularis L.) species of Jute (Family: Tiliaceae). The meiocytes mostly had 2n=14 chromosomes (prevalence of rod bivalents, evidenced at diplotene) at MI but in some species notable variation in chromosome numbers was recorded (C. capsularis: 6.94 II+0.13 I/ cell, C. olitorius: 6.79 II+0.42 I/cell, C. aestuans: 6.86 II+0.12 I/cell, C. fascicularis: 5.13 II+1.71 I/ cell, C. pseudocapsularis: 6.27 II+1.45 I/cell, C. pseudoolitorius: 4.83 II+0.44 I/cell, C. tridens: 6.85 II+0.30 I/cell, and C. trilocularis: 2.85 II+0.49 I/cell). All AI cells studied showed equal (7/7) segregation of chromosomes (excepting C. aestuans 97.56% and C. fascicularis 98.00%) and pollen fertility among the species varied from 37.67% (C. olitorius) to 84.29% (C. capsularis). About 15.19% (C. trilocularis) to 65.22% (C. tridens) of the PMCs at MI documented secondary association of chromosomes (2, 3, 4, 5 and 6 group classes were observed) and secondary polyploidy was attributed as the possible cause. Statistical analysis of cytological data revealed that the basic chromosome number in Corchorus spp. is 4 (x=4, n=7; selected doubling possibly). Preponderance of cytomictic behavior of chromosomes (only in meiosis I) was studied in C. aestuans (hypoploid 1.16%), C. fascicularis (hypoploid 12.54%, hyperploid 2.03%), C. pseudoolitorius (hypoploid 18.06%, hyperploid 6.94%) and C. trilocularis (hypoploid 54.43%, hyperploid 1.27%) resulting in numerical variation (only at MI) in chromosome numbers (n=1, 2, 3, 4, 5, 6, 8, 16 and 18) apart from normal (n=7). Results obtained were discussed and it was presumed that both secondary grouping of chromosomes and cytomixis were the outcomes of genetic consequences. © 2011 The Japan Mendel Society.