Nematode management care

The choice of crops for rotation or succession must take into account the presence of soil pests, such as root lesion nematodes. Pratylenchus brachyurus. The use of susceptible plants, throughout each agricultural year, could significantly contribute to the population increase in the area, in addition to favoring interactions with other parasitic microorganisms.

Currently, new technologies used in agriculture have contributed significantly to the increase in food production. This scenario is due to the numerous investments made by companies from various agricultural segments that insistently seek to generate solutions applicable to the main problems existing in the field, related to the occurrence of pests and diseases, which put production at risk. In this context, problems that occur in the seed, roots and aerial part of plants can be grouped.

If only organisms that can attack plant roots are analyzed, there is already cause for concern, as the solutions to these problems generally involve joint measures of extreme synchronization. In recent years, the incidence of nematodes has been increasing, which increases problems with the incidence of other soil pathogens, such as fungi, resulting in frequent losses of different magnitudes every year. As the symptoms can be varied, depending on the complexity of the interaction between phytonematode species and crops, several observed problems end up, wrongly, attributed to other factors, minimizing something that actually has worrying dimensions. A very clear example of this dimension is the incidence of root lesion nematodes Pratylenchus brachyurus which, according to recent studies, is widely spread across several producing states. Biotrophic microorganism (depends exclusively on plant roots to complete its biological cycle) has a high degree of polyphagy, (capacity to parasitize a vast number of plants from different botanical families), linked to its parasitism habit (migratory endoparasite). It feeds, in the initial stages of development, on the seedlings, causing numerous lesions that serve as an entry point for parasitic fungi in the soil, concomitantly infecting the root cells and ending up compromising the development of the seedlings and the initial stand. This process, in general, causes interference with the plant's physiological processes, compromises the absorption and translocation of nutrients and subsequently reduces productivity. Care in crop rotation or succession must be carefully analyzed, as it is an extremely polyphagous microorganism that is strictly dependent on the plant for its development. Sequencing, without due care, could increase the increase in this soil pest over the years.

Although this problem has been warned by many researchers and research institutions, the reflection of this is the countless cases, where the productive potential depends on good coexistence with this soil pest. It is worth remembering that its eradication or elimination, when established in any cultivation areas at levels of damage, is practically impossible, mainly due to costs or operational time.

To better understand the population dynamics of root lesion nematode, Pratylenchus brachyurus in different crops, the Phytus Institute, at its headquarters located in the municipality of Planaltina, Federal District, monitored a commercial grain cultivation crop (latitude 15°39'39.5"S, longitude 47°20'24.2"W and average altitude of 875m), with a history of the occurrence of this nematode since 2014. The aim of the work is to observe the population behavior of this nematode, in different crops throughout each year. Soil and roots were collected during the years 2014 and 2015. The points chosen for sampling were parts of the crop, expressing the typical symptoms of attack by this nematode, such as “borders” on the bean crop. These points were duly marked using geographic coordinates. Once collected, the samples were sent to the laboratory of the Experimental Station of the Phytus Institute, in the Federal District, where extraction and quantification of the population present in the soil and roots were carried out in 2014 and 2015 (Figure 1). 

The counts carried out in the nematology laboratory at the Phytus Institute showed a gradual increase in the population of P. brachyurus at the end of each agricultural year. Taking an average of the population values ​​in the five sampled points in 2014, the number of 374 juveniles and 393 eggs evolved to 2776 juveniles and 1156 eggs in 2015 (Graph 1). 

Analyzing the cultivation sequence implemented by the producer in 2014, it was observed that all crop or plant options used (soybeans, beans and corn) were susceptible to the root lesion nematode P. brachyurus, thus favoring its population growth. in the soil, which explains the high value diagnosed in 2015. 

It is also worth highlighting that, in 2015, the symptoms in all plants collected at the relevant sampling points presented a slightly more severe picture of symptoms than in the previous year, observing a marked yellowing in the aerial part of the plants, followed by strong underdevelopment . As a result, a laboratory analysis was carried out on the root and stem tissues of the plants, where the presence of the soil fungus was identified. Fusarium solani f. sp phaseoli. This fungus causes dry root rot, which is of great importance in bean cultivation and occurs in practically all producing regions in Brazil. After installed in culture, presents resistance structures on the surface or buried in the soil and enable survival in the cultural remains of host plants, making their control and management difficult. The symptom of dry root rot is the appearance of reddish-brown or necrotic lesions, with well-defined edges on the roots, leading to rapid deterioration of tissues located below soil level.

It is known that most plant parasitic nematodes can predispose plants, even if they are resistant to the action of phytopathogenic fungi that inhabit the soil. This interaction, although complex from a diagnostic point of view, must be somewhat common in areas where both pathogens are present, as in most of these cases, the damage is attributed to only one of the infectious agents. 

Crop rotation or succession has several benefits. However, the choice of crops used must consider the presence of this soil pest. The use of susceptible plants, throughout each agricultural year, could contribute significantly to the population increase in the area, with chances of also favoring interactions with other soil parasitic microorganisms.  

Janyne Moura dos Santos, Paulo Sergio dos Santos, Jéssika K. F. M. Lima, Iago Pereira Xavier, Instituto Phytus; Nédio Rodrigo Tormen, Univ. Federal District of Brasilia        

Article published in issue 210 of Cultivar Grandes Culturas.