Lim, Kar Yoong; (1992) Cytogenetic studies in evansia and laevigatae irises. Doctoral thesis (Ph.D.), University College London.

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Abstract

This thesis investigates species status and evolutionary relationships in the section Evansia and the series Laevigatae of the genus Iris. Within the Laevigatae attempts to synthesise disomic alien addition lines between I, pseudacorus and I.ensaba were also undertaken. In Evansia, the investigations were primarily centred on recognised Asiatic species. Comparative cytological analyses and experimental interspecific hybridisations had established their species status and taxonomic affinities. Additionally, two underscribed 'new species' - I "nova" and "I wittii" were identified and assigned to the Group I Evansia. Induced allopolyploids, generated from colchicine treatment of interspecific FI hybrids were obtained in 5 combinations and one combination (I. wattii x I. tectorum) could be considered as a new 'synthetic species' by its regular meiosis and high fertility. In Laevigatae, comparative cytological analyses and hybridisation studies elucidated species relationship particularly with respect to the previously suggested allopolyploid origins for I. versicolor and I. virginica. Attempted allopolyploid syntheses from colchicine-induced interspecific FI hybrids were successful in one instance while from crossing induced autoploid species forms, fertile vigorous allopolyploids were obtained in two instances. Following the discovery of alien monosomic addition cytotypes in the F2 progeny from an I. pseudacorus x I. ensata Fl. hybrid, karyological analyses of F2 and backcross progenies showed that 11 of the 12 I. ensata chromosomes could occur with the I. pseudacorus complement as monosomic or double monosomic alien additions Progeny studies also showed that the transmission of the alien chromosomes occurred mainly but not exclusively through the ovule. The frequency of transmissions were highest for the metacentric chromosomes ..ind included the longest and the shortest in the I. ensata complement. An attempt to synthesise disomic alien addition karyotypes was successful only with the smallest chromosome (No. 12) where 3% of the progeny had disomic karyotypes. The occurrence of a haploid and a triploid amongst the F3 progenies suggested that the presence of an alien chromosome could influence the maturation of the egg.

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