A supernumerary isofragment inGliricidia sepium (Jacq) Steud

Abstract

An earlier report of chromosome numbers of 2n=22 andn=11 is confirmed forGliricidia sepium (Jacq.) Steud. A supernumerary isofragment chromosome (SIF) in 32·41% of the nuclei at diakinesis and 30·00% of the PMCs at metaphase I is reported in the genus for the first time. The occurrence of the SIF was not consistant even in the PMCs of the same anther. Often the SIF exhibited inter-arm (fold back) pairing and behaved irregularly during meiosis probably due to a very weak centromeric activity. There seems to be a certain affinity between the SIF and one of the two nucleolar bivalents. It is hypothesized that the SIF could have arisen as a result of a disarticulation at the secondary constriction of a chromosome of one of the two nucleolar bivalents. The SIF has originated probably during one of the pre-meiotic mitoses in the sporogenous tissue since it was absent in some PMCs of an anther and in the somatic cells (of root tips and leaf tips). The SIF was mostly subjected to meiotic elimination through the formation of micronuclei (15·2%). In the other PMCs it is probably included in the microspore nuclei. The presence of the SIF or a deficient nucleolar chromosome in the pollen grains is considered to be responsible for about 8·15% of pollen sterility in excess to the normal. Neither uniform nor significant effects of the SIF have been noticed on meiosis nor does it produce any discernible morphological effects.