Re: [aroid-l] self pollination of aroids

From: "Julius Boos" ju-bo at msn.com> on 2003.05.20 at 09:28:30(10275) Dear Marc and Friends, Thank you for your most informative and interesting comments! I think we both agree completely without realizing it! I am not an expert on these matters, but was trying to determine/illustrate that apomixis was at least as good and perhaps better than self-pollination, as perhaps there was more and different genetic material available in apomixis for continued and later cross-pollination in a population of plants that were started by just one good seed originally produced from cross-pollination, but growing all by itself in a remote area. I thought that perhaps reproduction by apomixis (vs. cross-pollination) until there were a few plants in this new population to enable cross-pollination to begin may be 'the better of two evils' as it were, but obviously not as 'good' as cross-pollination in a large and thereby very genetically variable population. Julius +More >>>>>Dear Julius, and Friends, I have many comments on your last message. You are right Julius, there are two phenomena : self-pollination, that is the fertilization of ovules by its own pollen that will consequently lead to the formation of seeds. Apomixis that will lead to the formation of (viable) seeds without any fertilization (e.g. no pollen needed) by "parthenogenesis/parthenocarpy" of some cells (you have about 10 kinds of apomixis according to the kind of cells implied: egg-cell, endosperm,.). In the first case, two genetic informations are mixed whereas in the second just one genetic information is duplicate. As you mention for Urospatha and Xanthosoma acutum, may not present self-pollination as you observe that protogyny is complete (no overlap). Then apomixis is certainly present in these taxa. The best way to test it (without counting chromosomes) is to castrate (part of) inflorescences to see if just female flowers can produce seeds. In my recent study of Montrichardia (for those interested see attached file), I observe that bagged inflorescences produced seeds, but I was not able to distinguish between self-pollination and apomixis. Such answer needs a specific experiments. I suspect that apomixis is common in horticultural aroids as it's the case for many other families. Fig trees are a good example: about 700 varieties of Ficus carica, the edible fig, created by men. Half of them are parthenocarpic, they produce mature figs with (or not) seeds, but without the fig wasp pollinators (no pollen needed); the other half is more "traditional" and needs to be pollinated by the fig wasps (carrying pollen) in order to get mature figs. Consequently parthenocarpic fig species can be cultivated in areas outside the natural range of the fig wasp. I don't know if it's better to self-pollinated or to reproduce by apomixis, in the first case genetic recombination can occur and can create some variability, but inbreeding can cause low seed set. Some apomictic Rubus species which are self-fertile have developed in a second step self-pollinating mechanisms. Apomixis occurs in many taxa thus it must advantageous in some situations. In many cases, its origin may be from sexually sterile hybrid polyploids (with high genetic diversity). Advantages : Assured reproduction (seeds formation) in absence of pollination (sexual partners) or/and pollinators. Clonal reproduction equivalent of vegetative reproduction 'Cost of meiosis' and the mother genetic contribution 100% (instead of 50%) to her offspring Fix and disseminate an extremely fit genotype. Disadvantages : Accumulate disadvantageous mutations Inability to recombine novel mutants A very narrow niche/habitat No adaptation to stable habitats (often weeds in transitory habitats). You thoughts were right except may be about which system is more advantageous. I don't know if it helps!!!! Sincerely yours, Marc

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