Apple scab

Of the approximately 100 varieties of local Navarre apple trees analysed, twenty-two showed that they were especially resistant to fire blight and apple scab, two of the most damaging and economically harmful diseases affecting crops. This is one of the results of the research undertaken in Navarre and in which researchers Jesús Murillo Martínez, Alejandro Martínez Bilbao and Amaya Ortiz Barredo from the Public University of Navarre took part, together with Emilio Montesinos, from the Agricultural Food Technology Institute at the University of Girona.

The results of the research, led by Jesús Murillo, professor of Plant Production and lead researcher of the Crop Protection team at the Public University of Navarre (UPNA), were recently published in the Euphytica scientific journal, seventh in its category in impact factor. The research was initiated with 103 varieties of local Navarre apple trees, from a collection of 253 maintained by the Navarre Technical Institute for Agricultural Management (ITGA) in Sartaguda and Santesteban and included in UPNA’s apple tree germplasm bank. The first stage involved researching the incidence of fire blight and then work was focused on finding out about resistance to the different varieties of apple scab.

Fire blight, caused by the Erwinia amylovora bacteria, is a plague that causes important losses when it attacks apple or pear crops, given that the only solution to date is the drastic pruning of the trees or their complete elimination. As regards the apple scab, this is caused by the Venturia inaequalis fungus; it is one of the most important diseases of the apple tree and affects leaves and fruit.

According to researcher Alejandro Martínez-Bilbao, “we found 22 varieties that were particularly interesting for their resistance to the two diseases. The 22 are not very sensitive to fire blight and show varied resistance to the fungus causing the apple scab and, of these 22 varieties, five were outstanding for their agricultural qualities”. In concrete, these five varieties of apple for cider making are known as “Erremedio”, “Merealiña”, “Xarpaxar”, “Peaugon-Monsur” (origin Echauri) and “3.1.50” (origin Puente La Reina/Gares).

Avoid use of fungicides

The research overall took eight years to complete, two for experimentation and six for observation in the field at the ITGA experimental plantation station in Santesteban. The principal objective was to find out the resistance capabilities of the cider apple trees to these plagues, especially to apple scab. “It has to be taken into account that the usual treatment is the use of fungicides — pointed out the researcher—, but in commercial crop varieties it is essential to carry out a number of treatments for the tree to be completely free of disease and the fruit thereof to be commercially viable; moreover, the drop in production also results in the fruit being aesthetically less attractive”.

As a result, the field of applications is open: for example, with cider production, an organic type of production could be implemented and where fungicides are not used; or an integrated type of production, with more resistant varieties, the use of fungicides and phytosanitary products being in general less.

Another perspective points to the genetic enhancement of the varieties, using those that have proved to be more resistant to disease. “This will be more long term”, pointed out Alejandro Martínez, “because it is essential to undertake further research and see how these varieties can be implemented in order to carry out a programme of genetic enhancement through the crossing or cloning of these genes”. In this vein, “there are genes which, for 50 years now, have been used for making apple trees more resistant, but the pathogen changes and overcomes this resistance. One of the advantages that we have found now is that the resistances shown by these varieties, and now identified, are different from those that have been overcome by the pathogen”.

Of the 103 varieties analysed initially for fire blight, 48 turned out not to be very sensitive to the disease, meaning better resistance, and so do not have to be cut down. Then 92 varieties of apple tree were analysed in vitro, including the 48 previous ones. Of these, 22 turned out to be not only more resistant to fire blight, but also to apple scab.

* Elhuyar translation, published in www.basqueresearch.com

References

Martínez-Bilbao A, Murillo J (2005) Six strains of Venturia inaequalis are found causing apple scab in Spain. Plant Dis 89:908 (http://apsjournals.apsnet.org/doi/abs/10.1094/PD-89-0908A)

Martínez-Bilbao A, Ortiz-Barredo A, Montesinos E, Murillo J (2009) Evaluation of a cider apple germplasm collection of local cultivars from Spain for resistance to fire blight (Erwinia amylovora) using a combination of inoculation assays on leaves and shoots. HortScience 44:1223–1227 (http://hortsci.ashspublications.org/content/44/5/1223.full)

Martínez-Bilbao, A., A. Ortiz Barredo, E. Montesinos, and J. Murillo. 2012 Venturia inaequalis resistance in local Spanish cider apple cultivars under controlled and field conditions. Euphytica, doi: 10.1007/s10681-012-0723-z (http://www.springerlink.com/content/h58337m0071035x5/)