back / zurück
Abgeschickt von Darcy Gunnlaugson am 24 Mai, 2000 um 18:40:14
Antwort auf: Re: Cypripedium - virus confirmed von firstname.lastname@example.org am 18 Mai, 2000 um 08:13:32:
: No, plants do not develop immunity. Immunity is misunderstood concept in plant pathology. In addition, even if you do not see symptoms, it does not mean plants developed immunity. Dissapearance of viral symptom is called 'masking,' and it frequently happens with plants infected with virus.
This misunderstood concept also applies to us. For example, Chicken Pox infects a person usually as a childhood disease, and a person is contagious only for a short while around the appearance of symptoms. If one misses getting the disease as a child and contracts it as an adult, it usually a much more severe illness than if it occured while a child. In either case when symptoms disappear and one no longer is contagious, an immunity to the disease is suggested, as the disease is never again experienced. However, the virus has merely gone to sleep along the spine, but it may be activated as a new form in later adult life. So it was masked! If reactivated then it's called Shingles in it's new form, and a person manifesting the symptoms of Shingles (which is non contagious as Shingles) can give Chicken Pox to someone who has not yet contracted that disease. Often Shingles never occur, or if they do it is 40, 50 or more years after the outbreak of Childhood Chicken Pox. However, the virus has been there, sleeping, all along. I suspect this is likely the case with most viral infections in plants or animals. Even our innoculations to immunize, are often long term mild infections of the disease. So, I applogize for suggesting immuntiy after the symptoms subside, as a more appropriate phrase would have been "a developed resistance".
: Again, this does not mean virus dissapeared from plants. One thing I would like to mention is, some (many?) varigated plants do carry viruses, and the variegation is in fact caused by viruses.
I have been in discussion with this topic in other groups and the consensus seems to be that most variagation is not viral. However, as I pointed out in those discussions, this does not necessarily mean that there are not still many viral variagations, as variagation is horticulture is a large cross section, and even 1 or 2 percent would mean a fair number of viral infected cultivars. One would be wise to investigate.
: This might be true, but I would assume it was due to genetic diversity as well. The one carries resistant gene(s) might have survived because of reistance to the virus.
Agreed, resistance is a much better word, whether it is acquired or genetic.
: I am not sure if virus is 'usually' transmitted in this manner. It really depends on types/species of viruses.
Agreed..."usually" is again a poor choice of a word on my part. I will in future be more succinct and precise as I see we are moving from a forum of general principles into one that is very scientific.
The two most major viruses for orchids (ORSV and CyMV) are mechanically transmitted. However, vectors have not been found *yet.* In addition, many viruses are transmitted through seeds or even by pollination. Some suspect this might be the case with orchids (virus transmission via pollen).
This sounds quite possible and I had not considered it before. Those who grow from seed and use pollen regularly, have often been those the most affected when a virus breaks out amoung their orchids. Those using vegetative division as the sole means of increase seem to less affected. So pollen may in fact be a prime vector.
: This is just for your information, but no *mycoplasma* has been described for plants in a strict sense. It was more accurately called mycoplasma-like organism (MLO), and the relationship between two was rather unclear. Now the ones used to be called MLO is now called phytoplasma. The branching characteristics of poinsettia are caused by this organism, and horticulturally considered to be desirable.
Great to have this information.