“In the lab I have very fast pollen germination using sugar water with a little bit of boric acid. It is 40ppm boric acid and I think I used 7.5% sucrose. In two hours the pollen tubes can be 30x long as the pollen was wide. I wonder if after pollination one tries to gently mist some of this solution (without disrupting the pollen too much on the stigmas) on the stigmas if it can help promote better germination. In the lab boric acid is needed for rose pollen to germinate (for a long time I thought I was doing something wrong because in Krussmans Complete book of roses that detail was left out!).”
If boron is essential and sucrose is very helpful for pollen growth, it seems wise to apply these, especially on reluctant parents, as barring genetic incompatibility these are the likely limiting factors.