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.

06 October 2013

A community breeding project - the Golden Spring growout

Cooperative breeding
I’ve got too many lines of peas to explore- -the flurry of crosses I did when I first realised I could cross peas resulted in about 30 or 40 seeds to grow into F1 plants. But these F1 plants produce hundreds of F2 seed, across 5 or 6 various lines – too many to grow. I just selected a couple of the lines to grow out, and have been sitting on these bags of F2 seed, that hold some interesting genetic potential, with no space to explore them.

A correspondent (Damien) answered one of my whinging complaints by offering to grow some for me. Preposterous! My precious F2 seed? No way…

But I gave it some more thought, pondered, then cautiously asked for volunteers on the garden forum I frequent, Ozgrow, to help with one of the F2 lines, Golden Spring, a cross between Golden Podded and Oregon Spring. So AllyH, Raymondo, Aussiejumbo and Damien are now on board as F2 growout-ers. Get sowing folks.

As alike as two peas in pod – not.

I’ve posted before about the smart way to choose female and male parents when performing a cross between two varieties with one parent dominant and the other recessive in a particular gene, so you can check the certainty of a real cross in the F1 generation, instead of having to wait until the phenotypes start expressing in the F2 generation.

But what if the phenotype doesn’t exhibit classic dominant/recessive inheritance? A couple of weeks ago I found just such an occurrence that helped me sort out a mix up in one of my F1 pea crosses.

I want to introduce the hypertendril/semi-leafless trait into snow peas. This trait is widely used in field peas, where trellising isn’t an option. These plants develop extra tendrils, which grow together, and in dwarf or semidwarf peas helps them to knit together into a self-supporting tangle that reduces lodging (falling over). In the home garden this will minimize the need for trellising –  andanything that reduces maintenance is a good thing. Semi-leafless is a recessive trait, so I crossed male pollen from Delta Louisa into the female flower of Kaspa the field pea. But when I grew the F1 seeds out, two of the six or so seedlings were hypertendril. Strange.
Hypertendril on right, normal on left

My  only explanation is that the Kaspa flower had just started to shed pollen when I crossed it, so a couple of the ovaries in that pod must have selfed with Kaspa pollen.

A further bit of evidence was the leaf margins. Kaspa has toothed edges to the leaves, Delta Louisa is smooth. The two hypertendril “F1”s (that weren’t) had toothed leaves, but the other F1s (the real deal) had slightly toothed edges. This suggested toothed leaf edges exhibits intermediate inheritance, a trait that helped me sort out this mixed up cross in the F1.

Toothed margin on right, slightly toothed on left


But I am growing out the two hypertendril F1s, just to see…