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Agriculture

Another victim of the Xylella

Evidence is building up of the bacterium infestation in coffee trees

Now it has been confirmed: the bacterium Xylella fastidiosa, cause of the yellowing blight in orange plantations in São Paulo, also infects coffee plantations – and in the whole of Brazil. The contamination of the coffee trees may even be older. It is likely that the Xylella passed from coffee to citrus trees”, says the phytopathologist Osvaldo Paradela Filho, of the Campinas Agronomical Institute (IAC). In his opinion, only this could explain the occurrence of the disease in coffee plantations in Minas Gerais, Paraná and Bahia for at least 30 years, according to field surveys and reports he has gathered. This theory gains strength from two factors: the cicada (the insect that transmits the bacteria) flies only a short distance and there are practically no orange plantations outside the State of São Paulo.

“Every coffee plantation more than five years old is infected by the Xylella, to a greater or lesser degree”, says the researcher. In 1995, he proved the presence of the bacteria in coffee plants. At the Experimental Center of the Biological Institute in Campinas, the bacteriologist Luis Otávio Saggion Beriam prepares the experiments with a controlled infestation, to understand better the development of the disease known as atrophy of the branch of the coffee plant. Caused by zinc deficiency, induced by the presence of the bacterium, it becomes more powerful when the plant is submitted to a shortage of water. It impairs the growth of the coffee trees, shortens the internode (the space between the nodes) to a third of the normal size and reduces the size of the fruit. The consequence: productivity falls. Currently, Brazil produces 25 million 60-kg sacks, with exports worth around US$ 3.1 billion. The country’s share of the world market, which was 80% at the beginning of the century, nowadays is only 20%.

In Araraquara, the agronomist Li Wenbin, researcher at the Citriculture Protection Fund (Fundecitrus), proved the opposite: the Xylella can also move from orange to coffee plantations. In the greenhouse, Wenbin infected a hundred coffee seedlings with the citrus variety of Xylella and observed that the symptoms appeared. Now he will try natural transmission through cicadas, to confirm that the coffee Xylella develops in citrus fruit. There is more than a year’s work ahead, but there are signs that, theoretically, an infected orange plantation can infect a healthy coffee plantation. The good news is that there is 85% homology (similarity) between the genetic material of the varieties of Xylella that infest both plants.

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