Karyotype analysis of ten accessions of Hausa potato in Nigeria

Abstract

Plant species may be classified according to their karyotype features. Variation in chromosome features is believed to have accompanied evolutionary divergence of many plant and animal species. The cytological characteristics of crop species vary with geographical location of plants. Knowledge of the karyotype relationships can be explored for effective genetic and breeding studies, especially in crops like the Hausa potato (Solenostemon rotundifolius) that have not received adequate research attention. This paper reports the results of the karyotype analysis of ten accessions of the Hausa potato cultivated in some parts of Nigeria. The accessions were raised in plastic bowls containing vermiculite soil, from which root-tips were harvested for slide preparation and karyotyping. The conventional squashing in aceto-orcein of root tissues after heating was used. The tissues were photographed under Nikon Universal Microscope, equipped with an MC 100 camera. The chromosomes were then measured under x400 magnification using a micrometer. Results showed that all the accessions were diploid with somatic chromosome number of 2n = 2x = 64. The total length of long-arms ranged from 108.80 µm in accession Pankshin to 118.14 µm in accession NRCRI (1). The total length of short arms ranged from 81.88 µm – 89.34 µm. The total length of long plus short arms ranged from 199.88 µm - 200.06 µm. The mitotic phases varied with accessions. Similarly, the arm ratio, r-value, centromeric index, coefficient of variation, total form, intra-chromosomal index and inter-chromosomal index varied with the accessions. The accessions were grouped into four clusters: accessions Hong (1), Hong (2), Manchok and Gembu in cluster I; accessions Pankshin and Langtang in cluster II; accessions NRCRI (1) and NRCRI (2) in cluster III; accessions Bokkos (1) and Bokkos (2) in cluster IV. The principal component analysis showed that variation in the complement length and the centromeric position accounted for 99.997% of the total variation amongst the accessions. The study demonstrated that cytological differences exist in the Hausa potato. Some accessions showed close phylogenetic relationship, but others were distantly related. These differences could be explored for the improvement of the Hausa potato accessions cultivated in Nigeria.