Summary
The results of intensive meiotic studies, particularly of the karyology and chromosomal homology at the pachytene stage, in the sweet potato (Ipomoea batatas L.), which is a hexaploid (2 n = 90), have thrown considerable light on its origin and genome relationships. Using suitable criteria, such as relative length of chromosomes, centromere position, chromomere pattern, absence of light staining segments in one of the arms, presence of telochromomere etc., 40 of the 45 haploid chromosome complement at pachytene were identified and assigned to 19 chromosomal types. Among these types, eight were present singly; in six of the types, chromosomes were present in duplicate, and in two types, in triplicate. The occurrence of higher multivalent chromosomal associations such as hexavalents and pentavalents, in addition to the quadrivalents already reported, was recorded for the first time at the pachytene and metaphase I stages. The hexavalents at pachytene were resolved into three distinct types based on the morphology of the participating chromosomes. A maximum number of nine quadrivalents at the metaphase I stage and four in the incompletely analyzed pachytene nuclei were recorded. The constituent chromosomes of three of the quadrivalents at pachytene stage were identified. From these observations, it is suggested that (i) the three parental genomes are partly homologous (ii) two of the genomes show closer homology to one another than to the third and (iii) the three genomes differ with respect to one or more of the eight chromosomal types occurring singly. The available information rules out an autopolyploid origin for sweet potato and suggests that the parental genomes are from closely related taxa. The advantages are emphasized of pursuing similar studies in other American Ipomoea species to unravel their relationship with the sweet potato. Among other meiotic irregularities, a translocated chromosome and a chromosome carrying inversion were detected at the pachytene stage and the possible role they may play in varietal differentiation is discussed.
Similar content being viewed by others
References
Bhaduri, P. N., Ghosh, P. N.: Chromosome squashes in cereals. Stain Technol. 29, 269–275 (1954).
Gustafsson, A., Gadd, I.: Mutations and crop improvement. III. Ipomoea batatas (L) Poir. (Convolvulaceae). Hereditas (Lund) 53, 77–89 (1965).
Jones, A.: Chromosome numbers in Ipomoea and related genera. J. Hered. 59, 99–102 (1968).
Jones, A.: Theoretical segregation ratios of qualitatively inherited characters for hexaploid sweet potato (Ipomoea batatas L.) U.S. Dept. Agri. Tech. Bull. No. 1368, 1–43 (1967).
Jones, A.: Cytological observations and fertility measurements of sweet potato (Ipomoea batatas (L.) Lam.). Proc. Amer. Soc. Hort. Sci. 86, 527–537 (1965).
Krishnan, R., Magoon, M. L., Vijaya Bai, K.: The pachytene chromosomes of Ipomoea crassicaulis. Theoret. Appl. Genetics 39, 274–279 (1969).
Magoon, M. L., Cooper, D. C., Hougas, R. W.: Cytogenetic studies of some diploid Solanums, section Tuberarium. Amer. J. Bot. 45, 207–222 (1958).
Magoon, M. L., Ramanujam, S.: Nature of chromosome pairing in the genus Solanum Section Tuberarium. Ind. Jour. Genet. 21, 212–221 (1960).
Magoon, M. L., Ramanujam, S., Cooper, D. C.: Cytogenetical studies in relation to the origin and differentiation of species in the genus Solanum. Caryologia 15, 151 to 252 (1962).
Nishiyama, I.: The origin of the sweet potato plant. 10th Pacific Sci. Congr., Honolulu, August 21 to September 6, 119–128 (1961).
Nishiyama, I., Teramura, T.: Mexican wild forms of sweet potato. Econ. Bot. 16, 304–314 (1962).
Riley, R.: The diploidization of polyploid wheat. Heredity 15, 407 to 429 (1960).
Sharma, A. K., Datta, P. C.: Cytological investigations on the genus Ipomoea and its importance in the study of phylogeny. Nucleus (Calcutta) 1, 89–122 (1958).
Swaminathan, M. S., Magoon, M. L.: Origin and cytogenetics of commercial potato. Adv. Genetics 10, 217–256 (1961).
Swaminathan, M. S., Magoon, M. L., Mehra, K. L.: A simple propionocarmine PMC smear method for plants with small chromosomes. Indian J. Genet. 14, 87–88 (1954).
Stebbins, G. L.: Variation and evolution in plants p. 643. Oxford Univ. Press 1950.
Ting, Y. C., Kehr, A. E.: Meiotic studies in the sweet potato (Ipomoea batatas Lam.). J. Heredity 44, 207–211 (1953).
Ting, Y.C., Kehr, A. E., Miller, J. C.: A cytological study of the sweet potato plant Ipomoea batatas (L.) Lam. and its related species. Amer. Naturalist 91, 197–203 (1957).
Williams, D. B., Cope, F. W.: Notes on self-incompatibility in the genus Ipomoea L. 1st Int. Symp. Trop. Root Crops, Trinidad, West Indies (1967, in press).
Author information
Authors and Affiliations
Additional information
Communicated by F. Mechelke
Rights and permissions
About this article
Cite this article
Magoon, M.L., Krishnan, R. & Vijaya Bai, K. Cytological evidence on the origin of sweet potato. Theoret. Appl. Genetics 40, 360–366 (1970). https://doi.org/10.1007/BF00285415
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00285415