25 October 2013

Contemplating new pea crosses

tMy target yellow snow pea is a dwarf, double flowered, powdery mildew-resistant, sweet, big-podded pea.
My F4 plants of Tall Yellow Snow, a cross between Golden Podded and what I think was Yakumo, are just producing their first pods. But they aren't double flowered, nor disease resistant.

But one of my purple snow pea crosses Delta Louisa X Chamber of Death produced a double flowered green podded F2 that was tall, highly disease resistant, and with huge pods. I'm growing some of F3s of this plant just to see what happens - it was such an outstanding plant last year that I had to grow it out, even tho it was never going to produce coloured pods. Of the twelve of so F3 plants I'm growing, four are dwarfs. If they produce big pods, they might be likely candidates for a cross to the Tall Yellow Snows.

This would make a good cross since the two genes for powdery mildew resistance are both recessive, and the two multi-flower genes (doesn't matter which one I get) are also recessive, as are all the dwarfing genes - again, it doesn't really matter which ones I get.

I'm also wondering which way to do the cross - the usual plan is to do a cross so that the F1 plants show if the cross was successful. For example, when crossing a tall (dominant) to a dwarf (recessive), put the tall pollen on the dwarf flower, and if the cross pollination was successful, the F1 plants will be tall since the F1s should be heterozygous for tall. If however the F1s are dwarf, this indicates that the cross was not successful, and the dwarf plant has pollinated itself in the normal way. This is useful since it saves you from growing out unsuccessful crosses for two generations, (the population starts segregating in the F2 generation).

However there is the issue of maternal cytoplasmic DNA. This resides in the mitochondria and chloroplasts, the power machinery of the cell, rather than in the nucleus, and is only passed down in the maternal line. So if you are after robustness, then using the robust plant as the mother makes sense - it might be connected with the cytoplasmic genetic material so it's a good way of hedging your bets.

So today I'll be out in the vege gardens, looking for flowers that are just at the right stage of maturity.

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