Cactus / denegrii

I graft cactus seedlings to collect seeds from my own plants as soon as possible.
I nornally stop grafting when I could collect seeds from my own plants.
Obregonia denegrii is possible to collect seeds from my plants but number of seeds possible to collect from one fruit is very limited.
I grafted 5 denegrii seedlings to increase mother plants.
The photo is one of grafted seedlings. I sowed seeds on 8th October 2011.