The most common question I'm fielding on the internet has to do with blossom-end rot of tomatoes (BER for short). Diagnosing this tomato problem for gardeners is easy enough, but after diagnosing it for people they want to know why it is seems to only be affecting their Roma tomato plants.
[MBT] Everyone and their mother is asking me about BER. One thing that everyone seems to have in common is that it is happening on Roma tomatoes. I've Googled and many sources say that Romas are suseptible to BER, but nobody really explains why. Genetic? Something to do with the root structure of Romas (my guess) or something else?
I get it on my Romas, too, but also on 'Polish Linguisa' and 'San Marzano,' which are also elongated, paste-type tomatoes. You're on the right track with the structure question, but from what I've seen, it has more to do with fruit structure than root or stem structure. The research I read (you can read it here) seems to suggest that because BER occurs during periods of rapid fruit expansion, and because elongated tomatoes seem more susceptible to it than other tomatoes (and cherry tomatoes never get BER) that the elongated shape of Roma-type tomatoes is to blame. The idea is that calcium deficiency within the fruit structure itself is to blame, and that vascular walls in elongated tomatoes are less capable of transmitting adequate calcium levels to the blossom ends of the tomatoes. To test this, the researchers used a calcium spray (which I had always considered to be a crock, btw) on the blossom end of Romas, being sure to spray before any evidence of BER was present. On those Romas that received the calcium spray applied to the blossom end, BER was greatly reduced as compared to fruits that the calcium spray hadn't been applied to. So the idea is that because the cell walls of the tomatoes were able to absorb the calcium spray, BER was prevented -- suggesting that BER in Roma type tomatoes has a lot less to do with levels of calcium in the soil (or watering practices) than with the shape of the fruits themselves.It makes sense, especially when you consider that I can have whole periods of zero blossom end rot on my tomatoes, but my Romas and Polish Linguisas are rampant with it. The plants are in the same soil, getting the same fertilizer, same watering schedule, same mulch -- the only difference is fruit shape. I'd like to see someone graft a Roma plant onto the rootstock of a non-Roma to see whether the roots have anything to do with it or not -- seems like it would be easy enough to do, I just haven't seen anything about anyone doing it yet.