Talent Vharachumu was an undergraduate intern who is originally from Zimbabwe and attends university in Costa Rica. She is studying agricultural sciences and has become particularly interested in plant physiology, especially due to her time at the lab. Along with the work Talent did for the physiology lab, as is typical for an intern, she sometimes participated in work with other labs as well. She enjoyed this because it allowed her to learn many different things and meet more people. She hopes to be able to return to the lab to complete her masters.
She enjoyed her work at the lab because she learned more about plant physiology. Our goal at the tree physiology lab is to improve general tree health and make strides in understanding tree physiology better and more completely. To accomplish this goal, we do research with a whole plant approach. One such experiment is on how different plants respond to and are affected by heat.
Talent primarily worked on that experiment. She would collect leaves from a variety of trees in a variety of genotypes and perform a procedure on them to test how they tolerate the different temperatures. To do the experiment she used a machine that punches a piece of the leaf out, then placed the piece on a black disk that went inside a Ziplock bag, which was then placed in a container of water for 30 minutes. Then she’d record the chlorophyll fluorescence (photosynthetic energy conversion) of the leaves, given from a machine called the Fluoremeter. She also worked on another project with an infrared gas analyzer (Li-6800) machine to measure photosynthesis, gas exchange, and chlorophyll fluorescence.
When I asked Talent why she believes this work is important and why she thinks people should care about it she explained that the data she’s gathering helps us better understand the way climate change is affecting the planet, different environments, and plants in general. People who work in agriculture can use the data about which plants tolerate heat better to determine which genotypes to grow, which hopefully will increase plant yield and agricultural efficiency as temperatures warm. Talent also said it “…can help them reduce losses from low production due to high temperatures that are being caused by global warming.” This is useful because it allows growers to make informed decisions about what kinds of crops to plant as the climate and planet continue to change. I asked specifically what she would say to people who think they don’t have a reason to care about plants and she said, “They don’t care about plants, but they care about eating.”
There has been discussion lately about how effective are antibiotics in citrus groves. In order for these to take down Las, the bacterium that causes greening, they need to be moved in the vascular system, particularly the phloem, where Las hangs out. So, are leaf-sprayed antibiotics moved systemically?
This is the question some colleagues and I asked in a recent paper. We were following up on some of Nian Wang’s research that showed how trunk-injected oxy-tetracycline (which we’ll affectionately call “oxytet”) moved around the citrus plant, eventually reaching all parts. We had a few questions:
When oxytetracycline is sprayed on the leaves, does it move to other parts of the plant? This question addressed whether there is systemic movement at all.
How much moves? If there is systemic movement, what proportion of what is sprayed is moved.
Does it matter whether you spray on old or young leaves? Some growers try to spray when there is new flush? New flush has thinner cuticle (the waxy layer on the outside of the leaf). We thought that applying to new flush would allow more oxytet to get into the leaf.
In the same study we looked at some of the effects of heat treatment, but today we’ll just look at oxytet delivery. These trees did not have HLB, this is because we wanted to look at oxytet movement, not efficacy against Las.
What did we find?
Oxytetracycline did move into leaves that did not receive the spray.
How much moved? In one trial we found between 0.36-0.63 of the concentration in the leaves that didn’t receive the application relative to the leaves that were sprayed. But in the next trial we found between 0.27 and 0.34. So, although we did find oxytet moved into leaves that weren’t sprayed, a portion of what was sprayed stayed in the original leaf. The portion that didn’t become systemic probably is useless against Las because it isn’t moving through the vascular system.
It doesn’t matter whether you spray old or young leaves. We found the same concentrations in the leaves regardless of which leaves were sprayed. At first we thought this contradicted some previous work that showed that there was a decrease in delivery of nitrogen as leaves aged. However, taking a closer look at that older work, it turns out that delivery decreases from when leaves emerge until about 6 weeks. However, after this point delivery begins to increase again. This is because, although there is more wax on the outside of the leaf, this wax ages and forms cracks, which probably allow more of whatever is sprayed in.
How did we find this?
Some plants we removed all new flush, some we removed all old flush, and some we left all the leaves. We covered about 1/4 of the canopy of small trees with impermeable plastic. Then we sprayed the rest of the canopy. After the spray had dried, we removed the plastic. About 3 weeks later we sampled both the leaves that were directly sprayed and those that weren’t. Then we tested each for oxytetracycline content.
Is it enough?
We still don’t know whether the concentrations that made it do the unsprayed leaves were enough to reduce the Las levels, because we actually don’t know how much oxytet it takes to bring Las down in the plant. This study didn’t address streptomycin, the other antibiotic that is labeled to use against Las, so we don’t know whether it would move similarly.
Kaolin particle films are having promising effects in managing Asian citrus psyllid, but they also have effects on photosynthesis. To help dig into this, a new member has joined our lab: Juanpablo Salvatierra Miranda, or “JP.” He’s 4 months into his first round of experiments, and he’s already made some important observations. He’s focusing on the how photosynthesis changes over the course of a day – “diurnal photosynthetic dynamics” – in response to kaolin particle films of different colors.
JP comes most recently from his native Chile, where he was working for a private agricultural research company. He has experience in horticulture of vegetables, wine grape, and citrus. His Master’s thesis will consider how different colored films affect growth and photosynthesis, as well as how these affect the development of huanglongbing symptoms in the field.