Showing papers by "Central Tuber Crops Research Institute published in 1969"
TL;DR: It has been suggested that meiotic abnormality is not the cause of pollen degeneration in the material studied and a segmental allopolyploid origin of the present day cultivars of cassava has be suggested.
Abstract: Detailed analyses of chromosomes at pachytene and later stages of meiosis were made in a cultivated type of cassava Pachytene chromosomes are depicted on the basis of total length, relative length, arm ratio, amount and distribution of heterochromatin and number and position of chromomeres Idiograms showing details of all the eighteen pachytene bivalents in the haploid complement are presented and based on the average values of lengths obtained by accurate measurements of the bivalents in a minimum of 15 completely analyzable nuclei, the eighteen pachytene bivalents have been arranged and numbered in order of their decreasing length as chromosome I to chromosome XVIII The haploid chromosomal complement, inter alia, has three functional nucleolar chromosomes and six chromosomal types represented in duplicate Based on the data of the pachytene karyology obtained, a segmental allopolyploid origin of the present day cultivars of cassava has been suggestedBased on cytological data, it has been suggested that meiotic abnormality is not the cause of pollen degeneration in the material studied
38 citations
TL;DR: The course of meiosis was normal and over ninety five percent of pollen were found stainable and the urgent need for extending similar studies to other taxa in this economically important genus for unravelling phyletic relationships has been stressed.
Abstract: The detailed morphology of the pachytene chromosomes and microsporogenesis have been studied in a diploid (2 n=30) American species, Ipomoea crassicaulis (Bth) B. L. Robinson. Idiogram of the pachytene chromosomes is presented and taking advantage of the extreme precision that pachytene analysis can lend, karyological characteristics of the haploid complement have been worked out in detail and individual chromosomes are identified. The course of meiosis was normal and over ninety five percent of pollen were found stainable. The urgent need for extending similar studies to other taxa in this economically important genus for unravelling phyletic relationships has been stressed.
5 citations
TL;DR: The mode of origin of the tetraploid taxon and its relationship to the diploid was considered and, in view of the prevalence of preferential pairing, low multivalent frequency and high fertility, a segmental allopolyploid origin seems probable.
Abstract: A detailed comparative cytomorphic study of the diploid Ipomoea biloba Forsk. (2n=30) and a naturally-occurring tetraploid form (2n=60) was made. The extent of morphological differences between the two chromosomal types have been presented and discussed. These differences relate to leaf shape and size, pollen size and length of seed coat hair. The course of microsporogenesis was investigated from pachytene stage onwards in both the taxa. Based on these data and their geographical distribution, the mode of origin of the tetraploid taxon and its relationship to the diploid was considered. The close similarity in their exomorphic characters, presence of both the diploid nucleolar chromosomal types in tetraploid and the sympatric distribution of the two taxa are advanced as evidences in favour of the direct role played by diploid biloba in the origin of the tetraploid taxon. However, in view of the prevalence of preferential pairing, low multivalent frequency and high fertility, a segmental allopolyploid origin seems probable.
2 citations