Newswise — February 8, 2016 – Tall fescue, a grass important to the southeastern United States, has a fungal partner that is known to help it grow better and tolerate a harsh climate. But there is a catch: Some of these fungal endophytes produce chemical compounds that can be toxic to livestock. Many studies have explored the relationship between the grass and the fungus, but a recent paper in Crop Science is among the first to investigate the future of the association with regard to climate change.
The symbiosis between tall fescue (Schedonorus arundinaceus) and the fungal endophyte (Epichloë coenophiala), found mostly in tall fescue’s leaves and stems, was once thought to be relatively straightforward. But researchers at the University of Kentucky are learning that it’s not so clear cut. In particular, genetics can complicate the mutualistic partnership, says the study’s lead author, Marie Bourguignon.
“There is a tradeoff because the endophyte allows tall fescue to grow better in hot and dry environments, but because it produces alkaloids toxic to livestock, [cattle] cannot graze it all that much,” explains Bourguignon, now a doctoral student at Iowa State University. “We explored plant and endophyte genetics because preliminary results showed that sometimes the endophyte does not make the plant more resistant to stressful environmental conditions.”
This led the researchers to hypothesize that the plant–fungal symbiosis might behave differently in different climates depending on the genotype of the endophyte and plant. Bourguignon says they were interested in many things. “We know central Kentucky is going to be getting hotter but how will the endophyte and plant respond to the change?” she asks. “Is there a limit where it becomes unbeneficial? Or does it become more so?”
Additionally, she says researchers recently found endophyte genotypes that do not produce the livestock toxin. They apparently give the same benefits to the plant as the toxic one without poisoning the livestock, but she wanted to know if these so-called “novel” symbioses would respond the same to a changing climate.
The results showed that, indeed, the genetics of the grass and endophyte play a huge role in determining fescue’s response to warming. The team arrived at this answer by performing an experiment with four different tall fescue genotypes and four different endophyte genotypes, with two of the endophytes being non-toxic to livestock and two being toxic. Additionally, a set of four plants was left uninfected to serve as controls, making eight plants total per replicate field plot.
A set of these eight plants was then put into four different climate change treatments: one experiencing natural rainfall and temperature, a second that was 3C warmer, a third with 30% more precipitation, and a final group that experienced both the higher temperature and rainfall.
Infected plants were generally more resilient to the climate treatments than those not infected. However, a close examination of the results showed many nuances.
“The biggest thing we found is the important variability in response to environmental changes among all of those genotypes,” Bourguignon says. “In general, the endophyte brings benefits to the grass under future climatic conditions, but the degree of benefit varies across the tested genotypes. For example, endophyte presence stimulated biomass and tiller production especially after hot and dry conditions. But the magnitude of this effect depended on the plant-endophyte genotype.” Additionally, plants in the hotter treatments with the toxic strains of endophyte produced more of the harmful alkaloid. But again, this response varied across tested grass-fungal genotypes. Overall, Bourguignon says, the results confirm their hypothesis that an infected plant does not always perform better than uninfected counterparts. In reality, it depends on the plant’s genetics, the endophyte’s genetics, the interaction between them, and the environmental conditions they are responding to. Bourguignon notes that a limitation of the study is that it doesn’t isolate the effect of plant versus endophyte genotype. Rather, it evaluates four different symbiotic responses to the altered environmental conditions, but more research could get at this idea. While it would be great to be able to tell a farmer exactly what tall fescue and endophyte genotypes they need to sustain pasture production in the future, being aware of the complexity of the plant-fungal symbiosis is still helpful, Bourguignon says. “If you think planting a nontoxic endophyte-infected fescue will protect your livestock, it is possible that this endophyte will not help the plant persist well enough under our changing climatic conditions,” she says. “On the other hand, a toxic endophyte could become more toxic as temperatures increases. It is all very complicated, but if we continue studying these genotypes, maybe we can find an ideal combination. Few people have looked at all of these interactions: the plant, the endophyte, the environment, and genetics.”
View the journal article online www.dx.doi.org/doi:10.2135/cropsci2015.01.0020
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