This is why you don't overdo rooting hormones

[ysrgrathe]

I was trying to root some cultivars and was experimenting with higher concentrations of auxins. Cuttings were washed in 900ppm hydrogen peroxide, wounded at the base, dipped and then stuck. The first images below are of A.p. 'Summer Gold' rooted in 3000ppm IBA / 1500ppm NAA (Dip N Grow), 12 days after planting. The cuttings were kept under domes at 95% humidity with bottom heat at 85F.

The failure mode is very interesting: the leaves did not dry out, instead the petiole died and necrosis spread from the end of the petiole out into the center of the leaf. You can also see the wounded area died at the base. However, the buds are still healthy and when I cut the branch tissue it was green and healthy above the necrotic area.

Other interesting facts: all the leaves on this cutting died and dropped off, as did a couple of others. However, I have a 6 more that look perfectly fine. More interesting: I tried some Arakawa at an even higher concentration (4000ppm IBA / 2000ppm NAA) and they seem perfectly healthy -- even pushing new growth! So maybe even within a species there are varying responses to auxins among different cultivars.

This is why you don't overdo rooting hormones. At least -- that's the lesson I took from it. Would be interested to hear from someone like @0soyoung that might have more insight!

 

[Wires_Guy_wires]

To me this doesn't look like a hormone issue. None that i have seen at least in 3 years in the lab.

It seems the stem has rotted from the inside while the cambium survived.

I can vouch for the differences between cultivars and even within cultivars themselves. IBA response is genetic and epigenetic.

NAA is usually dissolved in KOH, that might have hurt them too much; first the acid from peroxide, then a base from lye.

 

[Wires_Guy_wires]

It might be informative to state what effect auxins in excess could have, so that we all know what to look for.

NAA specific:
- callus, callus and callus especially at wound sites
- inhibition of root formation
- malformation of new growth
- vitrification (turning glassy transparent)
- inhibited growth (can last for months, even years in some citrus varieties)

One of the reasons NAA is less used is because in a lot of plants, it doesn't do anything but inhibit things.

IBA/IAA
- no root growth
- dropping of healthy looking(!) leafs
- spindly, leggy, thin growth (internodes of feets in length) can last for a season
- future non-responsiveness for auxins (feedback inhibition; the plant learns there's too much auxin in it's system and scales up the threshhold to which it responds, sometimes to a thousandfold) this can last a lifetime.

Some of these responses are universal for PGR's, some are more specific to a hormone.

Trust me, auxin resistant plants are a pain in the ass to multiply. I have gathered a team of researchers to try and find a solution on how to get those 'mutants' to root, but the answer was: make seed. That's it.
That'd be fun if synthetic seeds were possible, but to convert tissue like that, you'd need an auxin response.. I'm not sure how plants can live like that since the auxins regulate nearly 300 processes, but literature hints they have less know auxins that could fill that gap somehow. These auxins havent been found let alone synthesised unfortunately.

 

[jmw_bonsai]

I was trying to root some cultivars and was experimenting with higher concentrations of auxins. Cuttings were washed in 900ppm hydrogen peroxide, wounded at the base, dipped and then stuck. The first images below are of A.p. 'Summer Gold' rooted in 3000ppm IBA / 1500ppm NAA (Dip N Grow), 12 days after planting. The cuttings were kept under domes at 95% humidity with bottom heat at 85F.

The failure mode is very interesting: the leaves did not dry out, instead the petiole died and necrosis spread from the end of the petiole out into the center of the leaf. You can also see the wounded area died at the base. However, the buds are still healthy and when I cut the branch tissue it was green and healthy above the necrotic area.

Other interesting facts: all the leaves on this cutting died and dropped off, as did a couple of others. However, I have a 6 more that look perfectly fine. More interesting: I tried some Arakawa at an even higher concentration (4000ppm IBA / 2000ppm NAA) and they seem perfectly healthy -- even pushing new growth! So maybe even within a species there are varying responses to auxins among different cultivars.

This is why you don't overdo rooting hormones. At least -- that's the lesson I took from it. Would be interested to hear from someone like @0soyoung that might have more insight!

Interesting. Since I don't pay to much attention to exact ppms, I am not great for giving good scientific data. I will tell you I have tried a water soluble IBA the last couple of summers with pretty good luck. I mix a weaker solution ~200ppm and do a full dip with the leaves. Like foliar feeding. I then do a quick dip of higher conc for the bottom tip ~1000-5000ppm maybe higher, LOL) but just a few seconds.

Its pricey compared to other rooting hormones. But if you feel like reading their website Hortus is the company.
http://www.rooting-hormones.com/IBAsalts.htm

I juts did ~400 2 weeks ago. I have mine under mist ~15min/20secs. I try all kinds of Acer cultivars. Ill give some details of progress towards the end of June.