Studies on Gene Frequencies of Polyembryony and Karyotype in Fluted Pumpkin (Telfairia Occidentalis Hook. F.)

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Abstract

Five experiments were performed to investigate the polyembryonic expressions and karyomorphology of fluted pumpkin (Telfairia occidentalis Hook. F.). The results obtained revealed three morphotypes of polyembryony which included twin, triple and quadruple, irrespective of the shape of the pod. The three morphotypes had side shoots that varied in length. Some were unequal, a few of them were almost equal, and many had rudimentary side shoots, which subsequently degenerated with time. Chi-square test between the pod shape and the embryo type depicted independence (χ2= 1.02; P= 0.90) between pod shape and the embryo type. The triple and quadruple embryo types had the highest and lowest frequencies of occurrence, respectively. The gene frequencies in the first year were 0.64 and 0.36 for polyembryony (S allele) and monoembryony (s allele), respectively. The derived zygotic frequencies were 0.41 for the homozygous dominant (SS); 0.46 for the heterozygous (Ss) and 0.13 for the homozygous recessive (ss). These summed up to 0.87 for the multiple embryonic traits and 0.13 for the single embryonic trait. In the second year, the zygotic frequencies for the homozygous dominant (SS), the heterozygous (Ss) and the homozygous recessive (ss) were 0.33, 0.49 and 0.18, respectively. These corresponded with the 0.82 for the multiple embryonic traits and 0.18 for the single embryonic trait. Chi square analysis showed that the gene frequencies in both years did not differ significantly (χ2= 0.017; P= 0.96). The results obtained from the cytological studies of fluted pumpkin revealed the interphase and mitotic stages of the cell cycle, and a diploid chromosome number of 2n = 22. There were traces of polyploids namely; aneuploids (2n = 22 + 1), triploid (3n = 3x = 33) and tetraploid (4n = 4x = 44) among the cells investigated. The karyotype consisted of 5 metacentric, 4 submetacentric, 1 subtelocentric and 1 telocentric chromosomes. The karyotypic analysis revealed that the chromosome pair number 5 is homomorphic in the female plant but heteromorphic in the male plant. The ideograms showed that the chromosome complement falls into 11 size class groups of one chromosome pair per class in the female and 12 size class groups with the 5th chromosome pair having two size groups arising from the non-identical lengths in the male. This would appear to implicate an XY system of sex chromosomes with homogametic XX female and heterogametic XY male in fluted pumpkin. In terms of the agronomic value of polyembryony, the triple (tri-embryony) and the single (mono-embryony) lines performed more impressively than the twin (bi-embryony) and quadruple (tetra-embryony) lines.

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