Yesterday, not much special happened. Philippe and I both used the spare time in the morning to work on some things that we did have time for to do whilst on the road. The afternoon we spent waiting at the airport and the evening predominantly in a taxi, Evening traffic was, well, let’s say, dense. It took us more almost 3 hours to travel the 20 or so kilometers that lie between the airport and our hotel near the CIP.
Today was definitely way more exciting. When Philippe went his way to check on his possible Ralstonia strains, I went to the Phytopthora lab to get updated. As with any research project and probably even more with these kind of exploring projects there was good and bad news.
Philippe had quite a meager score, only six or seven isolated bacteria from the samples. However, this makes sense in many ways. Many stem samples were quite dry and the plants were not wilted, so the bacteria are probably not very heavily present. It could also be that the methods used were not effective enough to extract the bacteria from the sometimes even woody sample and lastly it could very well be that these particular Ralstonia strains are viable but not culturable or maybe they are culturable, but on slightly different medium than the known Ralstonia from cultivated tomato. DNA test will now have to prove if and how many plants really contained Ralstonia and what these isolated samples exactly are. Pretty exciting!
I have learned that the isolation method with the sliced potatoes (which works well in the lab for Phytophthora strains from potato), does not seem to work at all. Nothing grew. This could be the way the potatoes had been handled and stored on our route. But, we cannot bring 18 degrees high humidity incubators during the trip, so unless some very different results come from this weeks samples, we don’t have to use this method again. Somehow that’s a shame, because carrying petri dishes around is way more hassle and also way more prone to contamination. One day last week, I had to throw half the petri dishes out, because they were contaminated during our travels. That meant that day, I could only use the potato method to store samples. Then again, P. infestans grows slow and there is still a chance that some mycelium appears on the tubers. But, I guess this is already a lesson learned: Bring more and cleaner petri dishes!
On the other hand, the technicians had seen actually numerous good looking symptoms on quite a lot of the leaves that we collected the beginning of last week. The bad news was that even though the symptoms were there, is was very hard for them to recover live Phytophthora from the leaves, because they were so dry. I think this is partly due to the used methods,which differ a lot from the methods we use in the lab. Here they wait for the leave to spontaneously sporulate and wash off the spores and sporangia and then look for them in the washed off watetr. This is highly diluted and often contaminated with other sores, so it’s not an easy task. In Freising we would force Phytophthora to grow directly on a plate with rich medium and only later we worry about how to get the isolate clean. This is something that I should have checked beforehand. These are not cultivated potatoes, so we might have fewer spores to start with and even with potato, they apparently have problems here every now and again, especially when it has been very dry. And it has been dryer than it should have been at this time of year.
Later in the day,I had a look at the some of the samples from the second half of last week and I’ve seen Phytophthora sporangia washed of from both S. pennelli and S. peruvianum. The samples from this week we only just brought in, so nothing can be said about them yet, so it’s looking quite well at in the end.
But the fact that so many samples from the first few days were negative, didn’t feel well to me. In my mind, rescuing Phytopthora from a leave shouldn’t be so hard and the symptoms were evident, so I was not really prepared to use molecular detection methods. Luckily, a few days ago, I came across a paper with a brand new DNA extraction method. This seemed like a good excuse to test this method and use molecular methods to detect the presence of Phytophthora in the leaves. We tried the method on 24 samples, including mycelium freshly scraped from a potato. By Monday we should have the results. If the results are negative, there are several other methods that we still can test and there is a whole batch of samples that have yet to be processed and I will also be bringing FTA samples with me to Germany.
To me, this trip was definitely a success. I have seen sporangia directly coming of samples from two different tomato species and sporangia from a third third species were prepared by the technicians and almost half of the samples are still waiting to be processed. The molecular results will tell us how much we might have missed. To be fully prepared for the next trips I will compare both isolation methods one on one when I’m back in Freising. I also have to work a bit on my route planning. Being almost without petrol or underestimating the driving time by about 4 hours are not very clever, but easy to solve!
I am fairly sure that most readers of this blog are predominantly here to look at the pictures of the tomatoes. So, I will not post any more updates on the results. If you are interested to hear more of my experiences and the outcomes, please do get in touch via email. If you want to see more pictures, I invite you to check this website again some time from February next year, when Philippe and I will go to the north of Peru to look for a few other tomato species in slightly wetter climates.