Re: [aroid-l] self pollination of aroids

From: "Julius Boos" ju-bo at msn.com> on 2003.05.20 at 09:12:39(10274) Thanks for the comment! In the genus Urospatha there seems to be true apomixis, as there are only a very few fruit produced on a spadix that has not been pollinated, and these fruit generally contain less that their full 'quota' of seeds, but there are viable seed produced in most of the few fruit, thereby continuing the reproductive process without cross or self pollination. Julius +More > It is important not to confuse apomixis (embryo produced without > pollination - so a clonal seed source) from parthenocarpic - fruit > forming without seed = no reproduction) > > _______________________________ > > Michael Marcotrigiano, Ph.D > Director of the Botanic Garden and Professor of Biological Sciences > Smith College > Lyman Conservatory, 15 College Lane > Northampton, MA 01063 > email: mmarcotr@smith.edu > voice: 413-585-2741; fax: 413-585-2744 > www.smith.edu/garden > www.science.smith.edu/~mmarcotr > -------------------------------------------------------------------------- --------- > "Art is the unceasing effort to compete with > the beauty of flowers and never succeeding." > Marc Chagall > > >>> gibernau@cict.fr 05/19/03 09:49AM >>> > 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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