The sequenced one

Today started not much different from yesterday. That said, Moquegua is much nicer in morning rush hour than Arequipa, but as soon as we left the city we hit the desert. Everything was flat and sandy again for miles and miles. Like yesterday, the almost straight Panamerica Sur motorway only made a couple of turns when we were nearing one of the two rivers that had to be crossed. After about 1,5 hour, we made it to the 3rd river and the city of Tacna. From here we went back in the mountains. Just like yesterday, the first 20 kilometers were still too low and too sandy, but as soon as we gained elevation and the rocky riverbed came closer to the road, S chilense appeared as well. We drove up to 3500 m and then went down on the other site. What we saw there was quite unexpected. After so many day with mainly sand,we were suddenly looking into a valley where many parts were green.

We decided not to sample at all on the way up, but to drive for another two hours from Tacna to a town called Tarata. (To keep things simple, yesterdays furthert point was a town called Torata). Together with Aurelien Tellier and other collaborators, I have worked on the creation of a reference genome for S. chilense. The sequenced plant came from a population with number LA3111 and this population grows on the outskirts of Tacna. However, shortly before we reached Tarata, I realised that our fancy 4×4 had drunk a bit more Diesel on the way up than anticipated. Or differently said, if we continued like this, we would probably not get back to Tacna with this tank of fuel. Our good hope of finding a petrol station in Tarata vanished when we saw how small the village was. To be sure, we asked a police officer and he pointed out that we just passed a Rural Petrol Station. We backed up and realised that indeed the sign was clearly there. Inside we found a couple of barrels with either Diesel or Petrol and a small lady who would happily sell us half a bucket of the first one. We could borrow her funnel to make sure everything ended up in the petrol tank.

With some extra fuel, we drove on and it did not take long until we found a site, or basically two sites that were both equidistant from the estimated coordinates for LA3111. Based on the description, we decided that it must have been the site closest to town. About 5 plants were growing on the left side of the road on the slope overlooking the town and a few others preferred to rocks on the right side of the road. So behold: below the origin of the plant that provided the S chilense reference genome.

After this highlight, we drove a bit further and found that even at 3050 m the Peruvian love their potatoes. A neat little potato field was not far away from this site and on our way down we would realise that there were a few other potato fields not far from (or even very close to) some S. chilense plants. The potatoes appeared to have been sprayed, but there were also some symptoms of late blight visible, thus indicating that it is in the area and can grow well.

On the way back we made a lot of stops and collected as many samples as we could to process back in our hotel in Tacna. I am now debating whether we will change the plan for tomorrow. The original plan was to drive up in another valley to find more S. chilense, but we have a lot of mountain samples and we could also try our luck on the coast. There are no recorded S. chilense specimens on any of the databases, but they could grow there as well. Luckily I have still the whole night to think about this.

The south

After a fairly relaxing day in beautiful Arequipa, we went further southwards today. In this area we will be able to find three species. The most dominant one will be S. chilense, but we could also encounter S Peruvianum and S. Corneriomullerrii. The general area is extremely, and that means extremely dry. But There are a lot of valley were rivers flow all year round or in certain seasons. Besides that, the area experiences a lot of very heavy fog. We experienced such fog already on our first trip from Lima. This fog is so dense that in the car you will have to turn on your windscreen wipers. It looks like you drive through a light drizzle. This of course creates perfect infection conditions. For the next week, we got a different car. Driving will probably a bit more comfortable, but we don’t have the nice working space in the back anymore.

From Arequipa we drove to the coast. Not far outside the city we started to see the first plants. Unfortunately, we were right in morning traffic and driving on a main road (connecting the Peruvian coast with Brasil), so we had to skip a lot of samples, because we just could not stop. We knew we would get some others later and on next trips we can definitely find a way to collect here as well. When the road got a bit quieter, unfortunately, the landscape also got flatter and more importantly, it got drier, so the frequency of plants along the road decreased from one every several hundered meters to basically none for about 50 km. But as soon as the hills came back and there were signs of riverbeds, the first plants reappeared. It is incredible to see how these plants look so healthy in such dry regions. But, like I said before. Mist is a thing here and they really capture the humidity. The warning signs for the “Zona Neblina” were everywhere and we saw several net installations that are used to capture water from the air to drink or for agriculture.

From this point, I think we saw well over a thousand plants scattered along the roads. Sometimes single individuals, sometimes large groups of plants. Very interesting to see. The dry landscape was sometimes interrupted by some very lush fields and even grazing cows, but this was of course only very close to the rivers. Overall, the landscape was rugged and beautiful. Some tomatoes seemed to look completely healthy, not a single brown lesion, whereas others had some sign of infection. In many cases, there was also considerable drought stress, so some leaves would start to turn brown. Unfortunately, this browning can look very similar to infection symptoms, so picking the right plants took a bit longer than we expected. The views made up for it though.

The evening we spent in Moquegua. a quiet medium sized town in a fairly green valley. Unfortunately I didn’t have much time to see a lot of the town, because during the day, we did not manage to find a space to process the samples, so I had to set up a hotel room lab. Then again processing infected wild tomato samples is strangely gratifying.