Hi, I am Asking a question and appreciate your answers. if 1 parent in a cross is dominant and stable for lb resistance will the f1 also be resistant or will both parents need to have resistance? Thanks!
F1 will be heterozygous (Lb/lb), resistant. Next generations will be unstable for resistance (sometimes resistance won't be present => lb/lb). Only a homozygous (Lb/Lb as the stable dominant parent was) line will be stable for next generations.
My experience with late blight tolerance - especially when using ph3 - is that it is slightly penetrant meaning that the homozygous crosses are more tolerant than plants that don't have a copy of the gene but are less tolerant than plants that are homozygous for the trait. The homozygous trait is necessary to have reasonably good field tolerance.
Post by Tom Wagner on Mar 14, 2012 20:24:31 GMT -8
Each year for the last five years it seems that Ph-2 ...homozygous and less so with heterozygous lines confer early onset late blight resistance to some degree and folks make lots of claims for those being resistant. It lasts, depending on the severity and races of blight, for a few days and then it succumbs. Heterozygous Ph-3 has some protection for a while and it too dies for me...I am sure that only the homozygous Ph-2 and Ph-3 in tandem offers the best resistance. Having only one parent carrying the Ph-2 and Ph-3 such as Mountain Magic have not been enough here in Western Washington for the last five years.
I am including a photo of an early prototype clone carrying homozygous Ph-2 and Phi3 from the October 2007 season. All of the other varieties are dead including those like Mountain Magic. If you look closely at the picture, disregarding the weeds in the foreground, one single plant is still alive and blooming and no blight on the fruit either.
I don't know how the blight does in every other area but I am quickly introgressing both genes into all kinds of heirloom tomatoes. My website was supposed to have Magic Trick and Skykomish listed but too many orders have came in to list them after the fact. I had the master list ready and it was only partly uploaded by my webmaster. Sky Reacher is segregating for both genes...but not many folks seem to realize the value of that clone. Neither has Schrapnellmine...found a lot of hits for orders. Many others listed have Ph-2 bouncing around.
Magic Trick even has a bit of frost resistance and it takes a light frost quite well. Only well a hard freeze sets in that the plant dies like it got hit by blight.