«Xylella has a wide range of host plants, so the transmission returns if adequate phytosanitary measures are not established»

Interview with Manuel Barrera, Project Manager from the Sociedade Agricola da Herdade do Charqueirao, partners of the LIFE Resilience project.

Although its impact on the olive tree is better known, Xylella fastidiosa also affects other crops such as almond. What risk are these crops in Spain and in other European countries?

The risk cannot be quantitatively assessed in terms of data on affected plantations because it is not generalized in any area of ​​the Iberian Peninsula for now, but it can be assessed as a maximum risk because the only means of control is “no expansion” of the bacteria, since, today, there are no curative measures. That is why control through research on the improvement of resistance to this pathogen is vital.

It is true that its impact on the cultivation of the olive tree is best known, but precisely in the eastern part of Spain there are affected almond plantations, in which the appropriate measures for its control have been established. Given the boom in almond tree cultivation in recent years, the intensification of these and what is the exchange of plant material from one area to another, even within the peninsula, makes the risk of propagation multiply exponentially. In addition, it influences that Xyllela has a wide range of host plants so the transmission is again in question if the appropriate phytosanitary measures are not established.

At the SAHC farm, the Life Resilience project tests are carried out on almond trees, what do they consist of?

The tests consist of finding responses of plants (in this case almond trees) to different alternatives proposed, working mainly on the possibilities of adaptation through crop management to favor its resistance to disease. From treatments applied through microorganisms, to deficit irrigation application, through plant cover implantation. The essays have three distinct pillars:

1. Pose the response of the plant to the planting of different seeds of plant cover. In this case, the planting of the vegetation cover with different seeds has been carried out, making repetitions to test the results and compare them with the result with bare soil and with the native adventitious natural vegetation cover of the area. The purpose of this test is to find vegetation whose host vector is not the same as the one used by the bacteria, even predator of these in a way that hinders the spread. Basically cover the soil of plants that house beneficial insects and repel Xylella vectors.

2. The application of deficit irrigation in the crop is based on establishing different zones with different irrigation doses, always less than the irrigation established for the crop as maximum irrigation. In this way, an attempt is made to seek an improvement in the resistance of the plant to stress situations and assess whether it would be extrapolated to improvements in the situations of phytopathological defenses. Obviously, only the experience of the trials will address practical results since it is not a quantifiable parameter.

3. Work with «microorganisms»: Avoid the application of current phytosanitary products, move away from the promotion of resistance of pathogens to the repetition of active materials and especially the commitment to the environment makes testing the planting with different natural treatments based on Microorganism is a priority point in this project. Plants develop different defense mechanisms against pathogen attack. After recognition of the pathogen, responses are activated that include the expression of genes associated with defense, one of them is the induced systematic resistance. The application of treatments with different microorganisms, at different doses and at different times of the year try to find positive answers for this study. These treatments are always applied to the soil and not by foliar route, and its foundation is based on improving and adapting the environment for the plant available when you need it.

What results do you expect to get?

The purpose is to differentiate positive effects on the plantation based on the different alternatives that are proposed, determine that the improved factors allow a synergy towards the resistance of the crop against the bacteria and raise patterns in crop management that reduce all variants that favor the development of the disease, such as the presence of vectors.

Obviously the trial is based on three well-differentiated variables, and we sincerely believe that in all three cases positive data can be obtained to a greater or lesser degree:

1. The improvement of the soil cover that allows to maintain biodiversity, but within it to be able to select the most appropriate to the most beneficial insects.

2. That the reduction of water consumption allows to stimulate the resistance of the plant to some pathogens such as Xylella.

3. The reduction of phytosanitary products and the development of more natural measures is a challenge with a lot of projection and from which really positive results are expected in the short term. To survive diseases caused by various pathogens, plants develop induced resistance mechanisms based on pathogen recognition and an immediate signaling response to activate defenses.

What is the importance of almond trees in the fight against climate change?

As in the rest of the crops in the Mediterranean area it is of vital importance, the decompensation of the phenological development due to temperature variations, the lack of rainfall and the rise in the average temperature affects the crop very negatively.

The latest planting trends mean that the number of hectares is constantly increasing, especially in irrigated areas where yields are so optimal. However, the more traditional almond tree plantations are in dry land where climate change is perceived with much more intensity, so that it can disappear. This opinion is extrapolated to many other crops of the Iberian Peninsula, since although climate change is present and global, there are some areas such as southern Spain where it is at the limit of being considered with almost desert climate. The periods of increasingly frequent droughts and, in addition, more and more wide they make change the conception of agriculture, development and type of exploitation of many plantations.