In this study the chromosome number, chromosome length and mitotic indices of 21 accessions of African Yam Bean (AYB) were determined. To accomplish this, the best time to harvest growing root tips was identified by measuring mitotic index of chromosomes prepared from root tips of accession TSs148 collected at two hours interval within a 24 h study period from 8 am to 6 am of following day. Cell division occurred throughout the day and at night with the rate of division increasing to a peak at midday. The highest percentage of metaphase cells (34.01%) was obtained from roots harvested at about 12:00 noon. In terms of the root tip to shoot tip that gave a higher mitotic index a ratio of 13:8 was observed among 21 accessions studied. A diploid chromosome count ranging between 2n = 20 to 24 was observed with the chromosome number 2n = 22 being the most frequent. The chromosomes of the accessions studied were generally small in size ranging between 0.58 to 1.84 μm. On the basis of chromosome size, the different accessions of AYB could be divided into three different groups. This information, if utilized, will pave the way for further progress in karyological and cytogenetic research towards improvement of this plant.
Key words: Sphenostylis stenocarpa, chromosome number and length, mitotic index, genetic variation.
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