When it comes to chestnut ink disease, comparisons between the European chestnut and the Japanese chestnut are inevitable. The first one produces larger and more commercially valuable nuts, but the second shows resistance to the disease in question. And it was this clue that led Susana Serrazina, a researcher at the Faculty of Sciences of the University of Lisbon and the Institute of Biosystems and Integrative Sciences (BioISI), followed, together with another team of scientists from various institutions, until she arrived at a solution with the potential to pave the way for chestnut varieties resistant to the disease, new treatments, or even methods for diagnosing an ailment that usually only becomes apparent when it reaches the trunk and “there is nothing left to be done”. Part of the research developed in the last years was revealed in a scientific article published in January by the BMC Genomics Journal.
BioISI is helping to develop a potential solution for chestnut ink disease
Susana Serrazina points out that there are genes which are activated by the Japanese chestnut tree but which are not activated, or are activated much later, by the European chestnut tree
“In the laboratory, we infected plants of the European and Japanese species and observed which genes each of these plants activated to resist the infection. “We have found that there is a set of genes that are activated by the Japanese chestnut tree but are not activated, or are activated much later, by the European chestnut tree,” explains Susana Serrazina.
Both the failure to activate and the delayed activation of genes ultimately limit the production of a protein similar to ginkbilobin, which has the ability to halt or mitigate the spread of ink disease in European chestnut trees. In contrast, in Japanese chestnut trees, the expression of genes that produce the protein increases significantly; consequently, ink disease is halted due to the secretion of a protein similar to ginkbilobin.
“Most likely, this protein will bind to the microorganism causing the disease and prevent it from spreading. “We know that a similar protein exists in the Ginkgo biloba species, and everything suggests that it is also produced in the quantities needed to halt ink disease in the Japanese chestnut tree,” explains Susana Serrazina.
'Flooding creates unfavourable conditions for the plant whilst at the same time creating favourable conditions for the Phytophthora cinnamomi'
Phytophthora cinnamomi is the name of the underground microorganism responsible for the disease that is the bane of farmers in Trás-os-Montes and other European regions that specialise in chestnut production. Scientists know it as an oomycete – and it is certainly no stranger.
The research into chestnut trees followed on from other studies involving cork oaks and holm oaks, which had yielded promising results using the same methodology, which focuses on the gene that may inhibit the oomycete Phytophthora cinnamomi. In addition to Susana Serrazina, who has been working at BioISI’s Laboratory for Research into Plant Stress & Signalling Lab, the research carried out on chestnut trees involved the participation of Elena Corredoira, of the Biological Mission of Galicia of the Spanish National Research Council (MBG-CSIC), (Santiago de Compostela), Rita Lourenço Costa, of the National Institute for Agrarian and Veterinary Research , IP (INIAV), and Marta Berrocal-Lobo, of the Centro de I+DI+ para la Conservacion de la Biodiversidad y el Desarrollo Sostenible (CBDS) of the Technical University of de Madrid (UPM), among other researchers.
“Flooding creates unfavourable conditions for the plant whilst at the same time creating favourable conditions for the Phytophthora cinnamomi”, adds the BioISI researcher, going on to provide further details: “Micro-organisms that lie dormant in the soil are activated by chemical signals produced by chestnut trees in response to root damage or waterlogged conditions, and produce motile spores in waterlogged conditions.”
Image of a chestnut tree with ink disease - Josemiriarte
What follows is more like a pirate ship’s boarding party, but in an underground version: the spores of Phytophthora cinnamomi are sent out with the aim of attaching themselves to the roots via tubes which, in turn, allow the intrusion and subsequent spread of the disease, eventually leading to the development of a network that feeds on the cells and will ultimately cause the tree’s death.
To date, there are no known effective chemical treatments, and ink disease is known to rot the roots of chestnut trees without humans ever suspecting it, until the tree shows signs of leaf desiccation and a darkened trunk, and the invasion by the disease-causing microorganisms has already irrevocably reached the plant’s vascular system.However, the researchers who authored the article in the BMC Genomics Journal admit to having found a potential solution, using genetic engineering techniques based on chestnut embryonic cells and bacteria. “We followed a similar approach to that of a vaccine,” says Susana Serrazina.
In the experiments carried out by the research consortium, a bacterium was used as a vector for Japanese chestnut genes, which infects the embryonic cells of European chestnut trees. As a result of this infection, the cells of the European chestnut tree come to incorporate the gene responsible for producing a protein similar to ginkgobilin. Given that these embryonic cells can give rise to future trees, this process will be sufficient to pave the way for new varieties of European chestnut trees, which have a genome that is suitably equipped to combat the Phytophthora cinnamomi.
‘If we have a suitable molecular marker, we can determine whether a particular tree is resistant to ink disease or not, and thus we are in a position to select the parent trees for breeding new varieties’
Genetic modification techniques were used during the trials, but Susana Serrazina admits that, in the future, the development of European chestnut trees that are resistant to the oomycete Phytophthora cinnamomi may undergo gene-editing techniques, which are more sophisticated and target only the specific genes. Given this level of precision, gene editing may be less subject to the regulatory restrictions applied to the production of genetically modified plants in the EU.
In addition to producing specimens that are more resistant to ink disease in the laboratory, modifying the gene for the ginkbilobin-like protein could prove useful for developing injectable treatments for diseased trees, or for using the gene that encodes it as a molecular marker to indicate a specimen’s resistance to ink disease.
“Crossbreeding between wild chestnut trees and domesticated chestnut trees is a natural occurrence. This means that we can find a great deal of genetic variation in the wild. “If we have a suitable molecular marker, we can determine whether a particular tree is resistant to ink disease or not, and so we are able to select, through simple tests, the parent trees for breeding new varieties of European chestnut trees that are resistant,” adds Susana Serrazina. At least in the laboratories, the campaign against the oomycete Phytophthora cinnamomi has already begun to take shape.