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Brazil develops varieties resistant to the main rice disease in Asia

The first Brazilian strains of rice resistant to the bacterium Xanthomonas oryzae pv. Have just been validated in Panama. Oryzae, the main pathogen that plagues the culture in several Asian and American countries. The disease has not yet been registered in Brazil. The new materials were developed by means of preventive genetic improvement, which studies the diseases and pests of the main agricultural species before they reach the country. , Under the Embrapa Labex-USA Program of the Secretariat of International Relations (SRI), and was supported by a partnership with the Agricultural Research Institute of Panama (IDIAP).

With this achievement, if the disease is detected in Brazil, farmers will already be able to rely on resistant plants of both irrigated rice, planted mainly in Rio Grande do Sul and dryland, grown in several other Brazilian states. The cultivars developed are adapted to the planting conditions of Brazil. "Many consider Xanthomonas the main threat of rice cultivation. The bacterium has already been introduced in countries close to Brazil such as Ecuador, Colombia and Venezuela and can enter the country at any time, "says the researcher responsible for the work, Márcio Elias Ferreira, Embrapa Labex-USA program and packed at the Beltsville Agricultural Research Center , In the state of Maryland, United States.


To develop the new materials, the researchers accessed the Embrapa Rice and Bean Germplasm Bank, home to 27,000 varieties of rice collected around the world. They identified three accesses, each containing a disease resistance gene. "We selected three broad spectrum resistance genes, that is, genes that promote simultaneous resistance to various 'races' of Xanthomonas. The genes were introduced in the same variety to develop plants resistant to various races of Xanthomonas, "says researcher Márcio Elias.


One of the advantages of studying preventively a quarantine pathogen is to know it in advance to know how to fight it if it is introduced in the country. "When a high-risk disease enters a country, the immedi- ate economic impact is very high. It usually takes a lot of time to develop symptom assessment protocols, to know the biology of the organism, to identify the resistance genes of the plants, to perform adequate crosses, to select resistant plants and to develop new cultivars. There are several steps that require a lot of time. Working preventively reduces costs and increases the efficiency of the process, "said the researcher, noting that even confirmation of the identity of the quarantine body can be time consuming. "We often have to send samples of plants infected with the new disease to specialists in the subject in another country so that we are sure that it is the same organism found for the first time in Brazil," he explains.


With the new varieties developed, in addition to anticipating a less costly solution to a future problem of Brazilian agriculture, preventive breeding also has the important role of enabling scientists to work with the disease or pest in advance. This leaves national agriculture much more prepared to face the problem when it finally crosses borders.


Paulo Hideo Rangel, Embrapa rice and rice grower and responsible for the project, stresses the importance of developing materials resistant to pests and diseases, adapted to the country's planting conditions. "It is often sought to combat an illness by importing a variety Developed by another country. As a rule, these varieties do not adapt to Brazilian conditions and are not very productive under our conditions, "says the researcher, stressing that the new cultivars developed by Embrapa are adapted to Brazil and present high productivity. Rangel, who is the coordinator of the Rice Germplasm Bank, also stresses the importance of conserving varieties of this cereal for the future. "Preventive improvement begins at the Germplasm Bank. The genes we are looking for are conserved in the thousands of varieties we store for present and future use in plant breeding, "he says.


Next steps


The resistance tests carried out in Panama were coordinated by the breeder Ismael Camargo and phytopathologist Felipe González, IDIAP researchers. They used isolates from the bacteria that are common in rice farms in that country. After the positive results obtained in Central America, the project team intends to test the materials also in Colombia through a partnership with the Colombian Corporation of Agricultural Research (Corpoica). "We know that our plants are resistant to the races of the bacteria that are in Panama, now we will see if they present similar performance compared to those present in Colombia. We want to offer the Brazilian producer a material with great chances of resisting a wide range of breeds of the pathogen, in case the disease is detected in the country, "says Márcio Elias.
The development of bacterial resistant rice varieties is done by the backcrossing technique based on DNA analysis. The scientists followed the genes transferred from three sources of resistance to rice varieties adapted to Brazil by analyzing the DNA of the seeds produced in several generations of the breeding program. The new strains possess the genes of resistance to Xanthomonas and, at the same time, they are very similar genetically to varieties that already are used in the Brazilian farms. "DNA analysis facilitates and makes the selection of characteristics already present in rice varieties planted by our farmers quicker and more efficient, with the addition of resistance genes to the bacteria," says Márcio Elias.


International partner is key


Making preventive genetic improvement with a focus on a quarantine disease requires international partnership, according to the researcher at Embrapa. In order to test, develop the materials and even study the disease requires collaboration with scientists from a country where the pathogen is already present. "There is no way to make preventive genetic improvement without the collaboration of scientists from other countries. Quarantine agencies are overseas and subject matter experts as well. Therefore, one of the first actions in the work of resistance to Xanthomonas was to sign a cooperation agreement between Embrapa and IDIAP of Panama. Recently, we signed a specific agreement for scientific collaboration in preventive breeding with the United States Agricultural Research Service (ARS-USDA) to conduct similar research with other agricultural species, such as beans, soybeans and vine, "says Márcio Elias.


Márcio Elias Ferreira is now dedicated to developing new varieties of black bean and carioca beans resistant to quarantine bacteria Pseudomonas syringae pv. Phaseolicola, an important bean disease in several countries. The work has identified three candidate genes for the control of the nine known breeds of the pathogen. This phase of the research should last two years and involves collaboration between several Brazilian and US researchers. The same approach is being applied to develop aphid-resistant soybean varieties Aphis glycines, a pest that plagues plantations in the United States and which fortunately has not yet been detected in Brazil.


Generating solutions for pests and diseases that have not yet arrived in the country is the most effective and economical way to combat these problems, according to the researcher. "When soybean rust arrived in Brazil in 2001, the country had not prepared for the disease. In the first year alone, more than $ 3.5 billion was spent on control measures, including the use of fungicides. It is estimated that 25 billion dollars have been spent since the introduction of rust in Brazil. Preventive measures, such as preventive genetic improvement, as well as reducing economic impact also limit environmental impact by minimizing the application of chemicals to fight disease or pests, "he concludes.