New species of root-knot nematode found in Brazil

Date:05-03-2021

Researchers from the Brazilian Association of Cotton Producers (Abapa), Embrapa Cotton and Bahia Foundation are observing a new species of root-knot nematode in Brazil which was discovered around 2012, in North Carolina (USA), but found in crops in Minas Gerais last year.

They measure 0.3 to 3 millimeters, look unattractive, and the damage they do is uglier. Phytomatomatoids, which in the agribusiness are simply called nematodes, are worms that attack the roots of plants and cause great damage to productivity, in crops such as cotton, soybeans and corn. Three native species from the cerrado attack cotton in particular. In order of occurrence, Pratylenchus brachyurus, also known as root lesion nematode, with 85% occurrence in Western Bahia; Meloidogyne incognita, called root-knot nematode, with 37%, and the species Reniform (Rotylenchulus reniformis), which has got this name because, when in adulthood, it gets the shape of a kidney. It occupies third place in the incidence podium in the productive areas, with 14%.

Although very common, Pratylenchus is not the nematode that causes the most damage. The root-knot nematode, on the other hand, is a huge headache, due to its potential for inflicting damage. As if that were not enough, now, the technicians of the Phytosanitary Program, in partnership with Embrapa Cotton and the Bahia Foundation, are eyeing another species of root-knot nematode, which, until then, was unknown in Brazil, and was discovered around 2012, in North Carolina (USA). Last year, the parasite was also found in crops in Minas Gerais.

According to Fabiano Perina, a phytopathologist and a researcher at Embrapa based in Luís Eduardo Magalhães, and a member of the Embrapa-Abapa-Bahia Foundation agreement, “What we want to find out is whether the worm is also present in the lands of the Cerrado in Bahia and not whether they migrated here via any vector. The discovery that they already existed is not known for how long, but they were unknown.”

The mining find happened because, in many farms, where the resistant root-knot nematode variety, the IMA 5801 B2RF, was used, the problem continued to occur. Now, researchers are checking the areas that use this variety, to see how they are developing. If they are not doing the job, it could be a sign that other populations of this - supposedly new - nematode species are present there. The technology has therefore become a “sentinel”.

Galls caused by nematodes are deformities that resemble tumors in the roots of plants and compromise their development. “It was deduced, then, that it was not the IMA5801 that was no longer effective, but another type of parasite, of the same genus, that escaped the eye of technology unscathed,” Perina said.

According to Antonio Carlos Araújo, coordinator of the Phytosanitary Program at Abapa, of the 18 members of the Fito Program team, formed by agronomists and agricultural technicians, 16 are dedicated to nematological research at this time. They collect soil samples, which are then analyzed by the Bahia Foundation. 

“With that, it is possible to make the diagnosis during the harvest, a job that is only possible thanks to the collaboration of farmers, who, proactively, open their farms for scientific research. Today, there is a special concern to discover evidence of this new root-knot nematode here in the Bahian savannah,” Araújo said.

Preventing nematodes

Once the infestation occurs, zeroing in on it is practically impossible. “What we can do is invest in a controlled coexistence with the disease, as a patient with blood pressure problems or diabetes does. He must always monitor and adopt measures to keep the indexes under control,” Perina stated.

These measures, according to the phytopathologist, are a combination of chemical, biological, genetic and cultural methods. The chemicals and biologicals are made through nematicides, whether they are active molecular principles, applied in industrial seed treatment or directly in the soil, or, in the case of biologicals, fungi and bacteria. Genetic methods refer to the use of resistant plants, and cultural methods refer to agronomic practices. 

“The more simplified the production matrix is, the worse. There needs to be diversity in the system. For this reason, crop rotation is essential especially when alternating cover crops, such as certain types of Crotalaria or Brachiaria, which are poor hosts or antagonists to nematodes,” Fabiano Perina explained.

The cultural aspect of integrated pest management includes the producer's decisions about the areas to be cultivated and, mainly, the cleaning of the machines. “There are at least three species of nematodes that are native and frequent in the cerrado, and here in the region, at least one attacks soy. They came here by hitchhiking on agricultural machines from other states. The machines are vehicles of contamination and dissemination also between the farms, or even between the different plots of the same rural property. Therefore, it is very important to clean it before use. A simple and effective measure,” Perina concludes.