Researchers to study how climate change affects leaf scorch


With more than a month-and-a-half until the official start of fall, some leaves are already withering on the campus of Saint Joseph’s University in Philadelphia, Pa. But it’s not the unusually intense summer heat that is shriveling the campus’s green foliage. It is the plant bacteria Xylella fastidiosa (Xf), which causes the disease known as leaf scorch.

Xf is a systemic disease that only occurs in the water-conducting vessels, or xylem of a plant, says biology major Will Puetz. He is researching the bacteria afflicting oaks on the campus as part of a University Summer Scholars research project.

“It affects trees on campus, and has gotten to the point where someone who can’t recognize the tell-tale signs of leaf scorch can still see that something is wrong with them,” Puetz says.

This research can have real applications on our campus

Saint Joseph’s Summer Scholars Program (SSP) gives students the opportunity to work with faculty mentors on research projects. Scholars are required to write about their work and present it publicly later in the school year.

The most notable symptom of Xf is the chlorosis, or scorching of the leaves, caused by bacteria blocking water channels. Because the disease is systemic, once a plant is infected it will eventually die. Spread by an insect called a leafhopper, Xf is not unique to Pennsylvania, and affects woody plants and trees worldwide. The bacteria can also be found in citrus groves and grape vines, resulting in a substantial loss of agricultural productivity.

“It hasn’t gotten a lot of attention, but it’s important enough that it is one of the first bacteria to have its genome fully sequenced so that we can understand the genetics of this disease,” says Assistant Professor of Biology Clint Springer, Ph.D., who is overseeing the research.

Puetz and biology graduate student Celia Del Cid are working to isolate the bacteria from infected trees and culture it, so that they can later test its effects on oak seedlings in a controlled lab environment. The duo will then be studying the bacteria with varying concentrations of carbon dioxide, which Puetz says can be used to simulate future environments, factoring in climate change.

“There’s a lot of research on this bacteria, but there’s very little information on the mechanism of stress it induces on the plant and how this disease will interact with climate change issues such as differences in water availability, changes in air temperature or changes in atmospheric CO2 concentrations,” says Springer.

Both Springer and Puetz say that the research could provide a clearer understanding of what to expect from the bacteria in relation to climate change. They will test whether elevated atmospheric carbon dioxide levels will help plants with the disease survive for longer periods, though Springer doubts they will be able to overcome the bacteria completely.

Puetz will also build on the research of Susan Jackson, M.S. \’07, whose work involved mapping infected oaks at Saint Joseph\’s. Puetz and Del Cid will track the bacteria’s progression since Jackson’s evaluations, hoping to better understand the rate at which it spreads.