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Localized the gene for resistance to powdery mildew in peach trees

Nectarina en desarrollo con síntomas del oídio (manchas blancas). Crédito: CRAG-IRTA.

Researchers from CRAG and IRTA precisely identify the region of the genome where resistance to powdery mildew is found in peach trees, a knowledge that is being used to reduce the use of fungicides in the field

Researchers from CRAG and the Institute of Agrifood Research and Technology (IRTA) have located the gene for resistance to powdery mildew in peach trees, a disease that causes great economic losses and a notable environmental impact due to the fungicides used to control it. The study, published in the scientific journal Horticulture Research, also provides new molecular tools that are already being used to develop and identify resistant peach varieties and thus achieve a decrease in the application of fungicides during production.

The peach is an important crop especially in temperate regions, where in 2018 more than 24 million tons were produced worldwide, with Spain being the fourth largest producer country. Commercial peach crops are susceptible to powdery mildew disease, caused by a fungus that infects fruits, leaves and shoots, directly affecting the quality of the fruit and the production capacity of the tree.

The fungus that causes powdery mildew, called Podosphaera pannosa, can be preventatively controlled by fungicides, but the application of these products is very expensive and harmful to the environment. An ecological safe alternative to fungicides is the development of resistant peach varieties through plant breeding, and the results of the new work developed at CRAG provide valuable information for achieving an integrated and more sustainable management of this disease.

Looking for the resistance gene

“Before this study, and thanks to the use of interspecific crosses, we had been able to locate a gene for resistance to Podosphaera pannosa from the almond tree, a species genetically very similar to the peach tree. Now, thanks to the use of genomic tools such as massive sequencing, we know with much more precision the position of this gene and what its function could be”, explains Iban Eduardo, IRTA researcher at CRAG and leader of the work.

Given the genetic similarity between the almond tree and the peach tree, fertile hybrids can be obtained between these two species, a fact that the research team had used to discover resistance to powdery mildew in previous studies. In order to more precisely locate the resistance gene, in the present work they analysed the DNA of more than 700 hybrids and identified those that contained recombination and, therefore, provided useful information. Resistance to the fungus was evaluated in these selected hybrids, which led to a list of 27 candidate genes for which the differences between almond and peach were studied, and their expression in the leaves of the hybrids during fungus infection was examined. By using all these techniques, the gene called RGA2 is the one that presented the most evidence to be the gene responsible for resistance to powdery mildew.

From almond to peach

Once the powdery mildew resistance gene from the almond tree has been located, it can be introduced into commercial peach varieties through targeted crosses and its subsequent selection through the use of molecular markers. Currently, researchers have already initiated the crosses in the IRTA peach breeding programme, and they are working to develop new resistant varieties, with all the economic and environmental advantages that they represent.

“The molecular markers that we have described in this study are helping us select resistant peach trees among all the plants resulting from the crosses. We also propose to use these breeding programmes to combine different genes for resistance to pests and diseases and thus increase the durability of resistance and the sustainability of crops”, concludes Neus Marimon, first author of the article.