Gametic embryogenesis and haploid technology as valuable
support to plant breeding see link below
Link: www.springerlink.com/content/h8744421g368509p/fulltext.pdf
Hi Henry.
Thanks for posting this highly technical article.
It is slightly out of my full depth of knowledge, but it was enough info for me to be able to follow some of the basic ideas put forward.
Are there any universal protocols for anther culture for roses about, or are they more cultivar/species-matched protocols (if they exist)?
By anther culture I am meaning to say induction of haploid plants through in vitro culture of the male sex cells derived from anther material.
Hi George,
Henry and I have tried anther culture in roses as well as other people. The best people have done was to get callus to form that is haploid, but was not able to regenerate it. I found with a student working with me that silver nitrate in the media was helpful in getting better callus growth and likely blocked ethylene receptors in the confined spaces in culture.
The most advanced induction method published is using irradiated pollen and using it for pollination and then extracting the embryos on the mother plant before they abort. A percent have been haploid. The compromised pollen can start seed formation to begin without fertilization and one needs to rescue the embryo before the endosperm fails. The French group of researchers that published this work (extracting diploids from tetraploids) report a mixture of haploid and non-haploid plants derived.
Another method that involves just being observant has led to the haploids I have obtained. Plants naturally have a small rate of haploid embryos as well as go up in chromosome number too with unreduced or 2n gametes. These mechanisms allow for variability in nature and opportunity for if there is an advantage to a different ploidy for some members to reach that ploidy. I have two haploids of Rise N Shine still alive and had two nice haploids of Dorcas, but have since lost them.
Periodically there is a plant that is smaller statured, etc. one may suspect could be haploid. It may not have characteristics from the suspected male as well as another clue. These can be counted for chromosome number and confirmed one way or another. Sometimes we get two embryos in the same testa. Sometimes one is a synergid that developed without fertilization, a cell that has the same DNA makeup as the egg. THere is often one larger embryo from sexual fertilization and then a smaller one.
Since I germinate my seedlings in baggies and transplant them out, I can observe them well as I pull off remaining pericarp tissue as I plant and notice a small embryo. I often then care for the small embryo with extra fervor to try to get it to survive (extra light, etc.). Many die. Additionally, as we go down in chromosome number like this, genetic load is revealed and unmasked as dominant alleles for many essential genes are not there anymore producing the gene product needed for strong survival, etc. So, haploids tend to be somewhat weak, especially in highly heterozygous crops like roses that can drag along a lot of alleles and mask them through dominance. After obtaining them and getting ones strong enough to live and mature nicely, there is often the next challenge of finding those that have enough fertility to effectively use. THe French group had to go through a lot of haploids before they found those with enough fertility to effectively use.
Hopefully this isn’t too discouraging. It is a good thing to strive for. Additionally, if you want to raise diploids, you can raise op seed of triploids or cross triploids with diploids and hope for some of them being diploid and moving forward with genes you wanted from a polyploid brought down to the diploid level. Myself and others have documented diploids from triploid parents.
Going from diploid and getting a haploid of it to have a monoploid has not been achieved yet in roses to my knowledge. I look closely for twin embryos in the same testa from diploid roses. It would be really helpful for sequencing the rose genome since there would typically be one copy of every gene. To take advantage of the benefit of completely homozygous doubled haploids we would need to go down to the monoploid level and then chromosome double using mitotic inhibitors from there. I suspect it would be challenging in rose as at the monoploid level we will have every gene basically exposed without the opportunity for typical dominance at any locus to mask a poor performing allele. Hopefully we can do it.
Take Care,
David
Hi David!
WOW! Thanks so much for that summary David, how fascinating this is.
I twice have discovered twin embryos in the one papery testa covering of Queen Elizabeth XOP seed. (I diidn’t try to germinte them). This would seem an unusually high frequency to me, given that i have not opened that much QE seed (maybe like ??50 achenes max).
Just for fun here, I also would like to show a pic of twin embryos (I found about 12 minths ago), within the one testa of an olive seed, here it is:
I thought nothing of it and discarded them both. Next time I might be more caring with them!