AOBPreview originally published online on June 30, 2004
Annals of Botany 2004 94(2):289-295; doi:10.1093/aob/mch139
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Annals of Botany 94/2, © Annals of Botany Company 2004; all rights reserved
Unilateral Incompatibility in Capsicum (Solanaceae): Occurrence and Taxonomic Distribution
1 Department of Horticulture, Faculty of Agriculture, Akdeniz University, 07059 Antalya, Turkey and 2 Department of Agricultural Botany, School of Plant Sciences, The University of Reading, Whiteknights, PO Box 221, Reading RG6 6AS, UK
* For correspondence. Fax + 90 242 227 4564, E-mail onus{at}akdeniz.edu.tr
Received: 21 January 2004 Returned for revision: 1 March 2004 Accepted: 16 April 2004 Published electronically: 30 June 2004
• Background and aims Unilateral incompatibility (UI) occurs when pollinations between species are successful in one direction but not in the other. Self-incompatible (SI) species frequently show UI with genetically related, self-compatible (SC) species, as pollen of SI species is compatible on the SC pistil, but not vice versa. Many examples of unilateral incompatibility, and all those which have been studied most intensively, are found in the Solanaceae, particularly Lycopersicon, Solanum, Nicotiana and Petunia. The genus Capsicum is evolutionarily somewhat distant from Lycopersicon and Solanum and even further removed from Nicotiana and Petunia. Unilateral incompatibility has also been reported in Capsicum; however, this is the first comprehensive study of crosses between all readily available species in the genus.
• Methods All readily available (wild and domesticated) species in the genus are used as plant material, including the three genera from the Capsicum pubescens complex plus eight other species. Pollinations were made on pot-grown plants in a glasshouse. The number of pistils pollinated per cross varied (from five to 40 pistils per plant), depending on the numbers of flowers available. Pistils were collected 24 h after pollination and fixed for 3–24 h. After staining, pistils were mounted in a drop of stain, squashed gently under a cover slip and examined microscopically under ultra-violet light for pollen tube growth.
• Key results Unilateral incompatibility is confirmed in the C. pubescens complex. Its direction conforms to that predominant in the Solanaceae and other families, i.e. pistils of self-incompatible species, or self-compatible taxa closely related to self-incompatible species, inhibit pollen tubes of self-compatible species.
• Conclusions Unilateral incompatibility in Capsicum does not seem to have arisen to prevent introgression of self-compatibility into self-incompatible taxa, but as a by-product of divergence of the C. pubescens complex from the remainder of the genus.
Key words: Capsicum pubescens complex, chile pepper, incompatibility, incongruity, interspecific hybridization, pollen tube growth, S gene
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