I’m reading the very interesting book, Return to Resistance that was linked in the landrace plant breeding forum. It seems that in a diverse landrace both horizontal and vertical resistance would be functional; the reason vertical resistance does not work very well in modern varieties is that they are not genetically diverse enough to have a large number of “tumbler” combinations, and so a pest with the right “key” can plow right through the whole population.
If this is the case, should it change how we cull diseased plants from our landraces? Is there anything we should or should not do to increase the chances of keeping both kinds of resistance strong in our crops? Should we maybe be less impressed by an absolutely perfect plant, which may just have happened to be unmatched this season, but might have very weak background or horizontal resistance? Should we maybe be looking for a few bites or spots on our plants, and choosing those that show a small amount, but only a small amount, of pest activity? Or would this be counterproductive?
Should I always select for the most vigor and resistance? I think so. If a plant is slightly distressed, it COULD be because of a genetic trait that would actually be adaptive in another context… but probably not.
But if I plant 5000 bean plants, and two of them are shining stars while all the rest turn out mediocre… obviously I should save seeds from more than 2 plants.
It’s probably useful to not cull too hard, but I also suspect that having maximum diversity in a single population is not as important as having diversity between populations.
Responsible selective breeding seems like a heavy issue to you and me, but it wouldn’t be so heavy if everybody in every corner of the world was saving local seeds.
I just finished reading the book, and reached the same conclusion that you did - that a landrace should have both vertical and horizontal resistances if possible. It seems to me that we should cull anything that doesn’t have enough resistances (of whatever kind) to produce acceptable food, and keep both perfect and somewhat-less-than-perfect plants. The perfect plant will (maybe) contribute vertical resistance to the landrace, and the somewhat-less-than-perfect plant will (maybe) contribute horizontal resistance to the landrace. (And of course in the first year, keep everything that produces anything.)
I found it really interesting that he dismisses vertical resistances in crops as more or less unworkable, given the assumption that a particular crop will not have enough genetic variability to make it work—but for landrace breeders, things are very different!
I also found the whole concept of vertical resistance to be very interesting. Before reading this, I didn’t really understand that there were two completely different kinds of resistance, and I certainly didn’t know anything about how they functioned in the wild. His explanation of the interplay between vertical resistances in annual/deciduous crops and their parasites, and the lack of such resistances in tropical, perennial vegetation, was amazing. (And how that explains why modern plant breeding has been of much less use in the tropics.)
In general, I’m just finding the book to be really mind-blowing. The theory explains so many different phenomena in such an elegant way. I had to stop and look up whether new crop varieties still have such a short lifespan—and sure enough, I found a bulletin from a professional wheat breeder explaining that the average lifespan of a new wheat variety is about 5 years before it loses resistance and has to be replaced.
Yes, I also found it brilliant and fascinating. Ultimately, though, I was frustrated that he didn’t take the final step and advocate developing landraces - even though he admires the indigenous landrace farmers in Africa and elsewhere, and credits them with saving maize cultivation after the professional breeders screwed it up. It’s like he lines up all the pieces and then … draws the wrong conclusion.
I suppose he felt that any commercial, mechanized farm needs a certain level of uniformity, and that what he was proposing would go nowhere unless he could show that uniform varieties could be produced this way.
Even if he wasn’t totally on the right track, his approach could still lead to major positive changes if it was adopted by conventional agriculture.