Alternaria alternata resistance

[Steph S]

Once again in 2023, we had an extended period of high temperatures and humidity in July, and once again the mystery blight was savage, to the point that I spent the time reviewing online and comparing detailed pics, and finally finding the typical ring spot pattern, diagnosed as Alternaria alternata.  AKA Alternaria stem canker.
This is not the same thing that I came to know years ago as 'Early Blight', which attacked lower leaves of susceptible plants in cool and wet conditions, making large ring spots always with a yellow halo, and easily managed by culling susceptible varieties and/or their lower leaves.
This one blows in the greenhouse windows and first appears as a 'scorching' of outer and upper canopy leaves.  The production of antho in the 'scorch' stage is suggested to be a plant resistance mechanism to temperature scorching, but further reading about Alternaria alternata revealed that it causes "leaf scorch" on carrot family plants, so I believe something similar is happening here, since the scorching stage invariable leads to brown ring spots with or without yellow halo, and eventually infesting new shoots in the axil, petioles and stems.  From what I read about A. alternata, it appears to be the "mother of all blights" with 380 alternate hosts and indistinguishable in the field from some of the "host specific" species it has spawned, being frequently found together with those subspecies as well.  Optimal temperature range is around 80-85F, with high humidity also a key condition, and high UV a condition for germination of the spores.  In some years (or in normal years) we would rarely hit the mark, or not for longer than a week, and my plants would recover afterwards and carry on. Now for some years in a row, our hot weather when it comes is right on the money for the blight, and it's lasting for weeks and is pretty devastating.

I've read that Alternaria resistance is common in cv's and I've seen a list of resistant plants, but haven't grown any of them.
Do any of you have experience with resistant plants, and if so what varieties do you recommend?
I'm also interested to find out how resistant they are in practice (since none are entirely immune).

All of my plants are susceptible to the leaf infection to some extent or at a certain stage in their life cycle - switching to fruit ripening is deadly due to ethylene favoring the pest vs salicylate pathways that provide some resistance.
I have always culled and not used stem susceptible varieties for breeding but there is no stem resistance currently in my Yellow Project, which means they will go down hard and fast with the stems infected.  Also very sad to see my Kelly's Island Rumpus looking very leaf resistant until suddenly it succombed in all parts including stems. 

So I have a problem on my hands, with the climate change weather.  And need to find out what germplasm I can use to help.

[Steph S]

I found this useful review from 2017, which names the known sources of resistance in wild relative accessions as well as cultivars.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5666701/
2017  Current Status of Early Blight Resistance in Tomato: An Update

"Younger leaves are more resistant to EB than older leaves because of high sugar content and glycoalkaloids (solanine, chaconine and solanidine) [6,87]. Therefore, a late maturing crop may appear EB resistant without even having resistant genes because of the high sugar content and glycoalkaloids [23,88]. Such a correlation of negative horticultural traits and EB resistance has created difficulty in phenotypic selection during tomato breeding."
"Generally, late-maturing, low fruit-yielding and indeterminate tomato lines are more EB resistant, which has impeded the development of high EB-resistant cultivars with desirable traits through phenotypic selection "
"EB resistance is affected by different factors including physiological maturity, plant type, growth habit and fruit load. More importantly, the existing EB resistance in cultivars is not enough,.."

This all makes sense and correlates with observations here, that plants appear to be resistant until they get into the fruit maturing stage.

"Although EB resistance has been identified in wild species, only a moderate level of resistance has been obtained in breeding lines and cultivars, and often, they are associated with undesirable horticultural traits like low yield and late maturity. Some desirable epistatic interactions between the QTLs and other segregating genes from wild germplasm may be lost while transferring alleles from wild to cultivated species, leading to the change in QTL effects in cultivated species [96]. Because of this, it is difficult to obtain full resistance as that of the original wild sources."
So I hope those of you working with wild species are keeping an eye out for foliage blight resistant plants. 

If there are any currently pledged that have outstanding foliage and stem health, I'd like to try them.

[Steph S]

So this year, 2025, I took a break from the big grow outs of tomato lines.  I grew only 7 tomato plants in the greenhouse and 9 kinds of potatoes outdoors, to see if there was any sign of cross infectivity the EB/alternaria issues.  As it happened, the 7 randomly gifted plants included one of the most touted for EB resistance (Celebrity), one that appeared resistant at the farm last year (Polbig), a couple of OP's that were parents contributing to my own lines (Black Cherry, Zolotoe Serdtse, Moravsky Div) and Pervaya Lyubov, early pink I've grown many times, and an unknown Clear Pink Early.
Alternaria Blight did turn up on potato leaves in the bed outside the greenhouse windows at the same time it turned up on the tomato plants.  Both Polbig and Celebrity lost some upper canopy leaves and axillary growth to the disease, so they did not appear resistant on that account,however both plants appear to be ripening their fruit without damages.  They also managed to set a reasonable amount of fruit in spite of extremely hot temperatures all season (I did use shade cloth as well).  Zolotoe Serdtse and Pervaya Lyubov, which were notable for setting in cool weather in other seasons, did not set well in the heat.  PL lost one fruit to blight but so far has ripened a couple alright, though they were on the small side, and appears to be making up for lost time growing a few fruit now that weather is more moderate.  Zolotoe Serdtse set only half dozen fruit and every one of them has rotted with blight before blushing although the foliage did not appear affected.   Clear Pink Early is only now going down hard with blight yellowing all over the plant, but it produced hardly any fruit first or last, so for my assessment, a bust.
The outstanding plant for resistance was Moravsky Div, which set decently in spite of the heat, and has been continually ripening them for the past month without any fruit losses and without any grooming, pruning or other attention. Taste has been especially sweet and good.
Granted that MDiv and Clear Pink were on the side that receives some afternoon shade, there is some possibility of a benefit due to the position.  Pervaya Lyubov foliage is still looking pretty good, but that can be accounted the low production of fruit.
Black Cherry did not get leaf symptoms of EB, although it lost a few to scorching.  The plant is absolutely massive and the fruit set high on the plant is pathetic.  Literally yards of plant for a couple of small cherries.

So the take away notes for this season:
seems to be separate resistance for fruit vs leaves vs stems ; 
MDiv is the only one that performed better than my determinate breeding lines;
Polbig set really well in spite of heat and only slowed down after upper canopy losses, but still not losing any fruit to disease.  I would grow it again or work with it for these traits.
Celebrity also has the heat set and fruit resistance, but they are smaller and later than Polbig.

 

[William Schlegel]

https://goingtoseed.discourse.group/t/early-blight-resistance/4243/5

This recently popped up as an issue on the Going to Seed forum. So, I offered there to make some initial crosses.

Sounds from your posts that Morasky Div, Black Cherry, Polbig, and Celebrity might have some utility? I have Black Cherry and Celebrity in my tomato variety collection, but I haven't yet made any crosses with them.

[Steph S]

I would give Polbig and Celebrity a plus for the fruit resistance, considering the losses on some others.  Moravsky Div did have a couple of fruit with BER later on but they did not develop the 'rings' pattern typical of Alternaria.  It did also benefit from the afternoon shaded position, but didn't lose leaf in a big way until after most of its crop was ripened on the vine.  Black Cherry did develop some leaf symptoms on exposed leaves.  When I took down the shade cloth I saw the upper leaves were affected.  I pruned them off, and it's been fine since then.  I would still give it a decent resistance rating.

I've read several comments that indeterminate plants fare better than determinates with Alternaria.  It remains to be seen.   But there's also a list somewhere of resistant plants, I will see if I can find it and post it.  I seem to remember Aunt Ginny's Purple has turned up on a couple of those lists.  I was thinking about trialing it next year too.

[William Schlegel]

This page from Cornell https://www.vegetables.cornell.edu/pest-management/disease-factsheets/disease-resistant-vegetable-varieties/disease-resistant-tomato-varieties/ suggests the following might be useful amongst genetics I may still have on hand.

Brandywine
Celebrity F1 (Several different generations)
Cloudy Day F1 (May have saved some F2 seed)
Coyote
Geranium Kiss
Homestead (For me via Home Stoop)
Indigo Rose
Matt's Wild

If I add Black Cherry to that list I have quite a few things to make crosses between.

I have a cross with Matt's Wild and a couple crosses with Home Stoop made this year. 

[William Schlegel]

I think I should add Mexico Midget to the list. I have it and its descendant Dwarf Eagle Smiley. My 314 cross is descended from Dwarf Eagle Smiley and I made 11 new crosses with 314 this year, Including Matt's Wild x 314. So, I might already have a few crosses that need testing for Early Blight and Alternaria resistance.

[Steph S]

Incidentally, I just realized I didn't post about 2024.  I trialed Mountain Gem, among others, which has one of the Alternaria resistance genes listed in that first article.  And Plum Regal, which is from the same breeding program.   These two did not fare any better than my own varieties with the blight.  (It wasn't as bad a year as 2023, the blight struck a bit later.  Sadly for Mt. Gem and Plum Regal they are much later than my own breeding lines, so it was a handicap. I lost some Mt. Gem fruit to blight. Plum Regal fruit were not affected as badly as the leaves, but didn't have time to ripen on the vine - they ripened nicely in a box.)
Since Black Cherry is a parent of my determinate lines, that would tend to agree that it has some useful resistance genes, which are as valuable in my environment here as the genes identified in the study.