Breeding for Late Blight Resistant Tomatoes

[Carol Deppe]

Too much nitrogen leads to very vigorous vegetative growth of tomatoes but late flowering and fruiting and less fruit production.

[ThomatoGarden]

Yes, too much nitrogen is probably the the biggest problem here,
mainly in the Greenhouse, much mulch and some fertilizer.
This and the crazy weather.

[Tim DH]

Hi Thomas,
    I've largely taken my eye off the ball regarding Blight Resistance. ... I haven't been affected since 2023!
    I am planning to raise some F1s with 'Endurance' next year, so hopefully, with that, and a bit of 'Latah' in my hybrids, that will be enough should Blight put in a re-appearance.

Tim DH

[ThomatoGarden]

Hi Tim,

Late Blight is present here every Year. There were always a few plants which were infected heavily.
On the other hand, i now have tested most possible resistant variety's and are at a point were
the majority of plants are at least partially resistant. Therefore i have no big outbreaks and
can concentrate more on other Resistances, Taste, Optics and Cracking. Without a base Resistance to
Late Blight i wouldn't be able to do this!
For me the Priorities are:
- Blight Resistance ,mostly achieved but still most important
- Cracking, In the field cracking can cause up to 90% loss (her atm after 4 days of rain) ,mostly
    achieved but in Crossings (many Primabella x Wapsipicon Peach) it can
    be naturally a Problem
- Taste
- other Resistances (Brunito F1 Alternaria)
- Optics
The Discovery that Brunito F1 is 100% Resistant to Alternaria (here atm !) is very
interesting, never saw this before. Not a single yellow leave! On top it has Late Blight but
the infection is slowed down, also interesting.
Sadly the Fruits are really hard and taste is also not good.

The Achievement and understanding of Late Blight Resistance gives me now the freedom to think
about other traits to cross in actual varieties.

[Roland]

I have Endurance here in the Netherlands. We have had an extremely hot and dry summer.

Endurance has potato leaves and produces cocktail-sized fruit. The flavour is fairly ordinary. Unfortunately, after a long period of drought followed by heavy rain this week, the fruits have proved to be quite prone to cracking.

For comparison, fruits from Rondobella do not crack under the same conditions.

[William Schlegel]

My plan with late blight breeding since it is currently a very rare occurrence here is to occasionally make crosses with known resistant lines. I attempted a new cross with the PH5 currant tomato and I added a free Galahad F1 plant to my garden this year. The older crosses with Galahad F1, Purple Zebra F1, and the PH5 currant are all included in various lines though often in dilute forms. For instance number 303 is 1/4 PH5 currant and 583 is 1/8 Purple Zebra. It would be interesting to have a rare late blight infestation or have someone with consistent late blight problems grow out some of my lines on an organic farm somewhere someday or do some MAS when some of these lines are stable. I don't think I have any lines stable that would make sense to do MAS with yet but if the OSSI grants program continues I'll work harder to develop some. I have the PH5 and PH3 currants so I would probably do something like cross those both with Purple Zebra and then cross those together and with some of the lines like 303 and 583.