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Agriculture

Natural combat on cultivated land

Fungi that are predators of worms harmful to several crops can be mass produced

A cocktail of five fungi may shortly become an important ally in fighting one of the most harmful pests for the cultivation of flowers and fruit and vegetables: root-knot nematodes (Meloidogyne spp.), worm-like animals similar to earthworms, but much smaller, measuring between 0.5 millimeters in their juvenile phase and 1 millimeter in the adult phase. They settle themselves in the roots of plants and cause visible alterations in the form of knots called galls that reduce the absorption and transport of water and nutrients by the plant, which jeopardizes or, in extreme cases, makes cultivation impracticable.

Agronomist Jaime Maia dos Santos, from the School of Agrarian and Veterinary Sciences of the São Paulo State University (Unesp) in Jaboticabal, proved that some fungi, normally found in the soil and harmless to crops, if grown in a special preparation of rice, are transformed into a powerful natural predator of this kind of nematode. “With the cocktail, we can think about carrying out a biological control of these pests, without turning to chemical products to kill off the nematodes”, comments Santos; if he finds a commercial partner, he will move on to mass produce his preparation of nematophagous fungi, with his eyes on the growing organic farming market.

The researcher believes that there is a demand for a cheap and ecological product like his mixture of fungi against nematodes. “I don’t know how much exactly the treatment with the cocktail would cost, but I can guarantee that it is very reasonable”, says the agronomist. Besides being expensive, chemical nematode killers can be harmful to the environment. To complicate the farmer’s life even the other options used to combat these worms – like, or using varieties of plants that are resistant to this farm pest – are little disseminated or out of the reach of the man in the country.

It is true that one still cannot say that the cocktail is the salvation of the crops, in terms of fighting the root-knot nematodes. They attack everything from plants like the bean plant to the rubber tree. The biggest losses are caused in the species of plants that take about 90 to 100 days to grow and to produce, the so-called short cycle crops, such as tomatoes, lettuce, cucumbers, melons and flowers in general. This is because, for the time being, the product has proved to be efficient only when applied in places where the crops are grown in greenhouses. “In open air plantations, where the temperature and the humidity vary a lot, the cocktail has not performed well”, says Santos, whose research was financed by FAPESP in two projects.

Flowers and greens
Another restriction, a temporary one, in the view of the scientists: up until now, the preparation against the nematodes has only been completely successful with crops of chrysanthemums (Dendranthema grandiflora). Experiments carried out with crops of cotton and oranges, which are usually attacked by species of worms similar to the root-knot nematode, indicate that the cocktail has not yet attained the effect that was hoped for. “But we believe that biological control is going to work with ornamental plants and greens in general”, says the agronomist. “So much so that we have started testing in greenhouses and in the open air with other species of flowers and with tomatoes”.

Santos’s enthusiasm over the fungus cocktail comes from the excellent results recently obtained in tests carried out at one of the great national centers of floriculture, the São Paulo municipality of Holambra. Tests done during the summer in hothouses on a property in the region, the Pedra Branca farm, showed that a variety of white colored chrysanthemum called Calabria responds positively to the biological control of nematodes. The productivity of flowerbeds highly contaminated by nematodes, where the soil, before the seedlings were planted, was given the fungus mixture was at least 30% better than the yield from equally infested beds that had not been through to biological control.

Innovation in the environment
Another benefit of the cocktail: the area treated with the fungus yielded flowers with stems of better quality, and larger in size and diameter. “This treatment is one of the main innovations in recent years, both in the technological aspect and in the environmental one as well”, reckons agronomist Jaime Motos, from Flortec, a company in Holambra that offers technical consultancy to producers from the region and took part in the experiments.

In the field research, the agronomists found that the ecological nematode killer can be applied to the hothouse soil before the flowers are planted, or in the substrate itself that is going to receive the seedling. Studies have also proved that the use of the cocktail, with its five fungi – Paecilomyces lilacinus, Arthrobotrys musiformis, Arthrobotrys oligospora, Dactylella leptospora and Monacrosporium robustum, this latter a species recorded for the first time in Brazil by Professor Arlete Silveira, a former member of Santos’s team – is more efficient for fighting the root-knot nematodes than the isolated use of just one or two species of these microorganisms.

These fungi are fast growing and have the ability to compete with other microorganisms in the soil. In addition, the fact that each fungus attacks the nematodes in a different way, and, at times, at different stages of the parasite’s life, may perhaps contribute to the success of this biological preparation. M. robustum, for example, pierces the eggs of the nematodes, which destroys them, a blow that helps to break the worm’s reproductive cycle. Some species of Arthrobotrys form rings in the pores in the soil through which the nematodes migrate. When these rings are penetrated by them, they contract and strangle the nematodes. A. oligospora produces sticky webs to capture the nematodes, break the body wall and consume the contents.

The stage for this battle is the soil close to the roots of the infested plant – and not in the insides of the plant. After the eggs have hatched, the worms leave the soil, penetrate into the roots of the host plants and remain there until the adult stage. There, they create the galls that lead to the rotting of the roots, jeopardizing the plant’s growth and its production. The estimate is that agricultural production may suffer a loss of over 10%, as a result of the activities of the nematodes.

A prodigy in the tests
Although the promising results of the fungus cocktail are still limited to one kind of flower and places with controlled growing (hothouses), the researcher from Unesp seems happy to know that his product is a viable alternative, at least, for protected crops. “The fungus is sometimes prodigious in the laboratory, but lets us down when we take it into the field”, Santos muses, having seen the effectiveness of these microorganisms in the fight against nematodes some five years ago, when he tried to control infestations by these worms in rubber plantations in Mato Grosso.

With a bit of luck and a lot of observation, the agronomists arrived at the nematophagous fungi. The researcher was not meeting with much success in controlling the pest, when he realized that, in an apparently spontaneous manner, without the help of any chemical product, some rubber trees got rid of the nematodes, while others had no such success. The fact intrigued him, and, after a number of analyses, Santos identified a great population of fungus in the earth, next to the roots of the trees that had gotten rid of the pest. That was how the idea arose of using the fungi found in the rubber plantations in Mato Grosso (also present in other parts of the country) as a biological control in other plants.

Nematodes in citrus
In another work carried out by a member of Santos’s team at Unesp in Jaboticabal, biologist Anderson Soares de Campos made a survey in the main orange-growing regions in the state of the occurrence of the so-called citrus nematode (Tylenchulus semipenetrans) and root lesion nematode (Pratylenchus spp.) in closed nurseries, in the open, and in commercial groves.

The results were worrying. A little over one third of the open air nurseries, besides three protected ones and three quarters of the commercial groves were infested with citrus nematodes, which act as parasites on the roots of the orange trees and lemon trees, and rob them of water and nutrients, which reduces the productivity of the crop by 14%, on average. In the same work, it was also found that a little less than 20 groves and at least seven open nurseries were infested by Pratylenchus jaehni, a new species, described in the scientific literature only last year by foreign researchers, with Santos’s participation.

To ascertain the incidence of nematodes in nurseries, Campos gathered 2,518 samples from 595 nurseries located in 99 municipalities of São Paulo. In the case of the commercial groves, the biologist analyzed 1,078 samples collected from groves in 86 municipalities. “In the orange plantations, the main form of infestation by nematodes is through the use of seedlings already infested by the worm”, says Santos. As of next year, it will be prohibited to produce, market and transport citrus seedlings produced in the open air, in the state of São Paulo. “Coupled with the fight against the disease in the orange groves, this measure should help to reduce the damage caused by nematodes”, Santos reckons. Support for putting this venture into practice is just one more battle embraced by the group from Jaboticabal, which hopes top make available to farmers, before long, the worm predator fungi.

The projects
1.
Morphological and Biochemical Characterization of Populations of Pratylenchus coffeae in Brazil (nº 99/09565-1); Modality Regular research benefit line; Coordinator Jaime Maia dos Santos – Unesp; Investment
R$ 44,463.93
2. Effectiveness of the Biological Control of Citrus Nematodes (Tylenchulus semipenetrans) with Nematodophagous Fungi (nº 00/15040-8); Modality
Regular research benefit line; Coordinator Jaime Maia dos Santos – Unesp; Investment R$ 46,485.00

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