Quote:
Originally Posted by crmauch
How many of the F2 generation would you usually plant? And of the resulting plants how many would you select to go forward? I'm thinking your numbers would get very large, fast. If in the F2 you grew 10 plants and 3 of those had traits you were looking for and grew out 10 of each of those for the F3 (you'd now be at 30 plants). If in the F4 you're still looking to avoid unwanted drift you could be looking at 90 plants. Are these the kind of numbers you would be talking about?
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Every "stable" variety of tomatoes is inbred to the point where there is essentially no meaningful heterozygosity left. With each successive generation there will be less genetic diversity to sample from. The upshot of this is that it would be most important to grow larger numbers in the early generations (F2, less so F3). Once you get a few generations down the line, the plants will be homozygous for most genetic loci and so each plant will be very similar to any other. Essentially we're managing and using drift to our ends, instead of avoiding it.
You only have to save seeds from one plant each generation, if you choose wisely which plant to save seeds from. I was growing out of one batch of seeds (F3s?) for one of my projects for several years (at about 4 plants a year) until I found a plant with better fruit last year. I'll probably be growing out of the seeds I saved from that plant for the next several years as well. I still have those older generations of seeds in storage if I later decide this lineage isn't turning out how I thought it might.