Managing nematodes in potatoes

The root-knot nematode is one of the most aggressive in potato cultivation, in tropical, temperate and subtropical conditions, with losses in production and the capacity to make commercialization unfeasible due to the depreciation of the tubers. Its management requires the integration of several measures, from pre-planting to harvest.

In Brazil, the main form of potato consumption is in nature. Therefore, the appearance of the tubers to be sold is very important, where any type of deformation or visual change makes them unviable for the market and consumption. Phytosanitary problems cause direct damage to the production or quality of potatoes, posing serious risks to the crop in practically all regions where it is grown. Among the pests that affect crops worldwide, phytonematodes represent average annual losses of 12%, and can even compromise entire production. In the country, several phytoparasite genera are found affecting the development of the crop, including the root-knot nematode (Meloidogyne spp.) and the lesion nematode  (Pratylenchus spp.) the main ones.

The root-knot nematode is considered one of the most aggressive to potatoes in tropical, temperate and subtropical conditions. These organisms are microscopic worms that penetrate the roots of potato plants, and induce the formation of galls (thickenings) on the roots, thus affecting the absorption of water and nutrients and, subsequently, causing “popcorn” in the tubers. Furthermore, plants weakened by the parasitism of this nematode can become vulnerable to secondary infections by fungal and bacterial pathogens that develop into wilting and/or rot.

even though M. javanica being the most common species of root-knot nematode in the different Brazilian regions where potatoes are grown, the occurrence of M. unexplained, M. arenaria e M.hapla, the first three being more adapted to temperatures with wide variability, and the last to milder climates.

Lifecycle

After hatching, the root-knot nematode develops its entire life cycle inside the plant root. Its life cycle involves four juvenile stages until reaching the adult stage (males and females) and can vary from 20 days to more than 60 days, depending on climatic conditions, the nematode species and the plant involved. This nematode can complete up to three cycles, and subsequently invade the tubers, making their sale unviable. Therefore, knowledge of the life cycle is important to make decisions to control this pest, as in different regions of the country cultivars are used that have both short cycles and longer vegetative cycles. However, more precise studies regarding the root-knot nematode cycle associated with genetic resistance are still incipient in our conditions.

Symptomatology

The main symptoms caused by gender Meloidogyne are characterized by the formation of galls on the roots of potato plants infected by the worm. When the attack is intense, plants wilt during the hottest hours of the day, which becomes irreversible over time. The appearance of “popcorn” may also occur, which generally appears when potato tubers come from growing areas with high infestation, which affects their appearance and subsequent marketing. Furthermore, infected tubers favor the spread of the nematode in new areas, if these tubers are used as seed potatoes, and it also contributes to the increase in the population in the area since some producers still prefer to leave the tuber in the ground rather than bear the costs. harvest costs, as they are not suitable for commercialization.

Nematode management

In order to reduce the damage caused by nematodes in potato crops, the cultivar, the planting time and the level of infestation of the soil in which the planting will be carried out must be considered. From these aspects, the most recommended measures to control nematodes in crops, under Brazilian conditions, are the planting of healthy seed tubers in areas without the presence of the pathogen and crop rotation with bad host plant species. The use of nematicides in crops requires caution in application.

The use of genetic resistance is considered one of the most desired control practices because it is economically viable and accessible to producers, and does not pose risks to human health and the environment. However, there are few genetic materials resistant to Meloidogyne spp. available on the Brazilian market. A similar situation occurs in relation to the lesion nematode, as even though it occurs in different potato producing regions in Brazil, little is known about the level of resistance of the cultivars sold in the country. Pratylenchus spp. Therefore, it is clear that for nematode control to be effective, there must be the integration of several measures, which range from choosing the planting area and seed potatoes to harvesting.

Research in progress

Currently, a series of studies related to the prospecting of sources of resistance to Meloidogyne spp. has been carried out by Embrapa, whose results relate resistance of some genotypes to certain species of root-knot nematode. However, there is still no commercial material with any resistance to M. javanica, being one of the points to be focused on by culture improvement programs. Likewise, work related to the pest's economic damage threshold, cultivation period and the quality of potato tubers destined for industrial processing has been conducted in partnership with the Federal University of Pelotas (UFPel) in the search for viable alternatives in management. from areas infested by root-knot nematode.

Jaqueline Tavares Schafer, Israel Lima Medina, UFPel; Cesar Bauer Gomes, Embrapa Temperate Climate.

Article published in issue 80 of Cultivar Hortaliças e Frutas