Parasitic Nematodes of Irrigated Rice in Brazil

Author and photos: Dr. Cristiano Bellé 

Coordinator of Nematology Research - Staphyt Brasil- Itaara/RS

Which nematodes affect rice crops in Brazil?

Many phytoparasitic nematodes are found in association with irrigated rice culture, affecting plant development and production. Among the most frequent in the crop are the genera Meloidogyne, Aphelenchoides, Pratylenchus, Hirschmanniella, Criconemella, Helicotylenchus, among others. The gall nematodes, genus Meloidogyne, form the group of greatest economic importance in agriculture. In irrigated rice, they attack the roots from which they extract nutrients for growth and development. As a result of root parasitism by these nematodes there is the formation of small swellings at the tips, called galls, whose presence hinders the absorption of water and nutrients needed for good plant development.

Among the species of the gall nematode that affect irrigated rice, Meloidogyne graminicola is considered the main cause of damage (Figure 1 and 2 ). Other species such as M. hainanensis, M. lini, M. incognita , M. javanica, M. arenaria, M. oryzae, M. salasi, M. sasseri, M. triticoryzae and M. ottersoni have also been reported parasitizing rice roots in the world. Rice plants attacked by Meloidogyne (gall nematode) show a large number of galls on the roots. The appearance of the roots resembles small umbrella handles. In addition, Meloidogyne can cause leaf yellowing in the aerial part, slow growth and reduced size, resulting in reduced production. Depending on the level of infestation, there is early flowering and wilting of the plants, sometimes leading to their death. In field conditions, there are spots in clusters containing smaller plants, associated or not with the symptoms described above (Figure 3). The damage caused by the root knot nematode varies according to the degree of resistance of the plants, its population density in the soil and water management in the irrigated area. Although rice is parasitized by at least eleven species of the genus Meloidogyne, M. graminicola has been the most studied species in irrigated crops. In Asian countries, in irrigated rice-growing areas, production losses due to M. graminicola attack vary between 20% and 80%.

Figure 1: Aspect of roots attacked by Meloidogyne graminicola. (Image credit: Staphyt)

Figure 2: Aspect of roots attacked by Meloidogyne graminicola. (Image credit: Staphyt)

Figure 3: Symptoms of rice plants in areas with the presence of the pinworm. (Image credit: Staphyt)

Although in Brazil in the state of Rio Grande do Sul, there have been reports of the occurrence of the gall nematode in irrigated rice since the 1980s in relation to the species, only in the 1990s was the presence of M. graminicola reported in the crop. In a recent survey, the presence of the species M. graminicola, M. oryzae, M. ottersoni and M. javanica, as well as three other nematodes with atypical esterase phenotypes, was reported in rice-growing regions of Rio Grande do Sul and Santa Catarina, causing damage to crops. In Paraná, a complex of species was also detected, predominantly M. graminicola and M. ottersoni. The identification of these Meloidogyne species by means of morphological, biochemical and molecular characteristics would be the first step for the future implementation of management techniques, such as the use of genetic resistance and crop rotation, which are essential for the maintenance or increase of national rice production.

Besides irrigated rice, other crops host M. graminicola such as black oats, barley, wheat, soybean, tomato, pepper and onion. Another factor that deserves attention are the weeds present in irrigated rice crops because, besides competing with crops for water, light and nutrients, they can be hosts for other pests, increasing future damage to the productive potential of the crop. Various weeds may harbor the nematode, including Echinochloa colonum, Echinochloa crusgalli, Eleusine indica, Fimbristylis miliacea, Cyperus difformis, Panicum spp. (Figure 4).

Figure 4: Weeds that host M. graminicola  (Image credit: Staphyt)

Development cycle of nematodes and risk of dissemination

The nematode survives and reproduces in the off-season, in fallow fields, contributing to an increase in population density in the soil, and then parasitizing the rice crop in the following season. However, weeds are often neglected by producers due to the lack of visible symptoms in the aerial part of the plants. In Brazil, this species has been found parasitizing roots of Echinochloa crusgalli, Cyperus difformis, Cyperus rotundus, Cyperus iria and Juncus microcephalus and has also been detected on Hordeum vulgare. In addition to this species surviving on alternative host plants, there is a danger of dissemination through water movement, contaminated farm equipment and utensils. Special attention should be given to irrigation water management in infested areas.

How to fight against nematodes? 

In order to reduce the losses caused by the root knot nematode it is necessary to reliably diagnose its presence in the area together with the correct identification of the species(s) associated with the crop. Among the control measures, the use of resistant varieties, crop rotation and the use of nematicides are more effective and economically feasible in the control of Meloidogyne spp. However, for the management of M. graminicola, there are no resistant varieties available in the Brazilian market, nor are there chemical products registered for rice culture in the country. Only four Bacillus-based products have been registered for M. graminicola management.

Biological nematicides applied via seed treatment and total area show a reduction in the population of these pathogens in the soil and roots of rice plants and with direct impact on productivity. This direct effect is linked to the mode of action of this management tool, which, by protecting the initial roots, guarantees the establishment of the plants by interfering directly in the process of infection of this nematode in the roots. When applied, it culminates in direct damage from its feeding in the root tissues and indirectly by opening the entrance door for other soil pathogens (Figure 5).

Figure 5: Plot treated with biological product on the left and untreated plot on the right, in an area naturally infested by M. graminicola. 

Because it is a group of difficult control and eradication is practically impossible, adding technologies that interfere in the interaction nematode-plant is essential for efficient structuring of the production environment, since these technologies have direct influence on the reproduction rate of the nematode in rice roots. In this regard, it is of paramount importance to reduce the population density of this nematode in the soil for the next crops.

Therefore, the producer should be careful in his choices when cultivating in soils with the presence of M. graminicola, seeking to use cultivars with low reproduction factor and associate this with the use of biological nematicides, in addition to intercropping rotation or succession of crops with non-host plants, in order to reduce the initial population from one crop to another, allowing the coexistence with these microorganisms.

How can Staphyt help you regarding Nematodes research in Brazil?

Staphyt laboratory based in Brazil (Conchal) is specialized in analysis of soil and plant materials for nematodes, with descriptions of species, population and race (SCN) levels.The research is focused on the mapping of phytonematodes, efficacy tests and development of molecules, chemical and biological, for the management of nematodes in different crops.

Staphyt can help with:

• Efficacy tests and development of chemical and biological products for the management of nematodes in different crops.

• Nematode mapping and diagnosis.
  

• Reproduction factor (FR) in different crops.
  

• Studies of cover crops in association with chemical and biological products in nematodes management;
  

• Positioning of nematicide/bionematicide
  

For further information do not hesitate to contact Staphyt: contact@staphyt.com

This article was initially published in AgroPages' '2023 Seed Treatment Special' magazine.

If you would like to share your company's story. Please contact Christina Xie at christina@agropages.com

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