CYTOLOGICAL STUDIES IN SOME WILD TUBER-BEARING SOLANUM

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Date
1983-06
Authors
SANGOWAWA, BENJAMIN GBEKELEOLUWA
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Abstract
Cytological studies were carried out in eight tuber-bearing wild Solanum species namely, 1. S. mochicense Ochoa, 2. S. boliviense Dun., 3. S. raphanifolium Card et Hawkes, 4. S. pinnatisectum Dun., 5- S. stenotomum Juz. et Buk., 6. S. chacoense Bitt., 7. S. kuntzianum Bitt. et Wittm. and 8. S. polytrichon Rydb. The haploid number in six species (1-6) is found to be 12 (n= 12) and they are therefore diploids and the two species namely, S. kuntzianum Bitt. et Wittm and S. polytrichon Rydb. are found to have 24. haploid number of chromosomes (n= 24.) and are therefore, tetraploids. Detailed meiotic studies have been made of the diploid and tetraploid species, and frequency of chiasmata in each species has been analysed both in diplotene and diakinesis and the terminalisation values of each of them have been estimated. Association of chromosomes in three or four or more are seen in diploid species. The frequency of multivalents have been analysed. The occurrence of multivalents in diploids indicate the presence of translocation heterozygotes. In tetraploids the percentage of quadrivalents varies from 47.58 to 57.42 in S. kuntzianum and S. polytrichon respectively, and this high degree of association of four chromosomes to form quadrivalents seem to indicate that these two species are autotetraploid in origin. The incidence of pairing of homologues in diploids and tetraploids have been analysed and the frequency of failure of pairing have also been estimated. The univalents which are formed due to failure of pairing among pairable chromosome mates behave in different ways in diploids and tetraploids. They either pass to the poles or lag between separating group of chromosomes or divide. The division and elimination of univalent causes unequal distribution of chromosomes in second metaphase and the frequency of these unequal distribution of chromosomes in diploids and tetraploids were analysed and the effects of these aberrations in the formation of morphologically good and deformed pollen have been studied. The formation of dicentric chromosomes involving chromatid bridges and fragments is found to be a usual phenomenon in the diploids and tetraploid species and their significance on sterility has been analysed and discussed. The secondary association of chromosomes occur in all species under consideration. There is preponderance of association of two over other groups of chromosomes in diploids and the significance of four groups of 2 and four free chromosomes has been discussed. The cytological behaviour of chromosomes in diploid Solarium under consideration indicates that there is a good evidence of regarding them as of hybrid origin. It is also apparent that the main lines of evolution in Solarium species investigated is that of interspecific hybridization and occurrence of polyploidy.
Description
A thesis submitted to the Postgraduate School, Ahmadu Bello University, in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY (with sixty eight tables and sixteen plates) Department of Biological Sciences, Faculty of Science, Ahmadu Bello University, Zaria. JUNE, 1983
Keywords
CYTOLOGICAL,, SOME WILD,, TUBER-BEARING,, SOLANUM
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