Biological Control Strategies for the Top 10 Plant Nematodes

The plant nematodes are small roundworms that also occur in the soil. Several types of nematodes are beneficial to plants. However, this paper focuses on types harmful to agriculture. This blog elaborates on various nematode parasites and their effects on crops. Understanding the significance of sustainability and biological control is essential. Identifying harmful nematodes helps in implementing effective management strategies.

Sustainable practices reduce the reliance on chemical pesticides. Biological control offers environmentally friendly solutions for managing nematode infestations. Integrating these practices improves overall agricultural health and productivity. Farmers can benefit from adopting sustainable and biological control methods. Effective nematode management ensures healthier crops and higher yields.

Root-Knot plant Nematodes

Meloidogyne spp. are among the most pathogenic species of plant-parasitic nematodes infesting a wide range of crops worldwide. These very small parasitic worms burrow into plant roots, inducing the formation of galls or “knots.” The galls interfere with the plant’s absorption of food and water from the soil. This interference significantly reduces the plant’s health and productivity. The nematodes’ activity can ultimately kill the plant. Farmers need effective strategies to manage Meloidogyne infestations. Crop rotation and resistant varieties can help control these nematodes. Regular monitoring and early detection are crucial for effective management. Integrated pest management practices are essential for sustainable control. Maintaining healthy soil conditions can reduce nematode populations.

Root knot nematode symptoms

This is not the kind of physical harm directly associated with root knot nematode damage due to exposure to root-knot nematodes. These nematodes impair the overall plant development making it to be under various stresses which include drought stress and nutrition starvation stress. Also, the damaged root system serves as a favorable platform for more infections from other pathogens. Such plants normally show decreased vigor and affected productivity in the form of stunted or dwarf plants, yellowing of leaves, and wilting of leaves in the infected parts.

Impact on Specific Crops

• Sugar Beets: Some of the most dangerous pests include root-knot plant nematodes that affect sugar beet cyst nematod. The nematodes pierce the root system and form galls that prevent the plant nutrients from such nutrients from plant roots. Furthermore, this reduces the sugar content of the crop and dramatically reduces the crop to cut back on yield as well.
• Cucumbers: The cucurbit root-knot nematode affects the development of cucumber fruits and the yield. The impact on economic returns: The fruits are small in size and therefore lower in the market prices reducing the economic returns to farmers.

Impact on the sugar Industry in Europe.

Root knot nematode is of great concern in the European sugar industry because of its effect on sugar beet. These nematodes have been reported to cause huge financial losses when they infest crops. Tangerine root galls form on the roots that prevent the movement of water and nutrients throughout the plants which leads to reduced crop production as well as low sugar content in the fruits.

It is important to note that any loss in sugar beet production in quantity and quality impacts all the stakeholders along the supply chain from farmers to processors and eventually the consumers. This is assuming because the sugar beet cyst nematode production in such highly affected regions and therefore control of the root knot nematodes is very crucial for the sustainability of the economically as well as the quality of the sugar produced.

Cyst Nematodes 

Heterodera and Globodera, known as cyst nematodes, form their bodies on the roots of host plants. They create sacs encasing their eggs, which can remain alive and fertile in the soil for up to ten years. In some cases, these eggs stay viable for several decades. This dormancy ability makes cyst nematodes persistent and difficult to control. They can inhabit soil for long periods, surviving adverse conditions and crop rotations. Cyst nematodes wait until the right host plant emerges. When the host plant appears, they hatch and reinitiate their life cycle. Effective management strategies are necessary to control these pests. Understanding their dormancy and lifecycle is crucial for effective control.

Soybean cyst nematode damage

This means that the prevention of cyst nematodes from inhabiting the soil adversely affects the roots of plants. The effect of the infection is that the nematodes colonize the root tissues, forming the feeding sites around the root tissues which disrupt the ability of the plant to uptake water and nutrients. This disruption results in manifestations, which include retarded growth of plants, yellowing the leaves and declining health of the plant. It more or less has reduced the efficiency of the root system Therefore, plant growth and development are greatly affected, leading to deficient crop production and quality.

Impact on Specific Crops

• Soybeans: The soybean cyst nematode is a major pest to soybean production worldwide Heterodera glycines. The cyst nematode symptoms include invading the roots and establishing facultative haustoria, which result in the formation of characteristic cysts on the roots, reducing the yield by 40 to 80 percent. Suffering soybean plants usually exhibit symptoms including nutrient deficiency, retarded growth and reduced pod production.
• Beets: Heterodera schachtii affects beets and is currently seen as a regional threat. It causes beet root necrosis by feeding on the plant roots, restricting the uptake of nutrients and water. This nematode affects plant health and reduces its yield significantly. Loss of up to 80 percent in beet quality may occur. Yellow leaves and wilting are common symptoms of nematode infestation. The quality of the roots also deteriorates and becomes less marketable. Effective management practices are essential to control nematode damage. Regular monitoring and early detection can help mitigate the impact. Implementing crop rotation and resistant varieties can reduce nematode populations. Farmers need to adopt integrated pest management strategies for control. Maintaining healthy soil conditions can minimize nematode infestations.

Another serious problem that should be addressed is how to control cyst nematodes; this needs to be done through crop rotation, the use of resistant varieties and biological controls. It is very important to study their biology, as well as their behavior, because they are significant pests for agriculture.

Root Rot Nematodes

Pratylenchus species are migratory endoparasites that infect the roots of various plants, causing significant damage. These nematodes are highly pathogenic with devastating effects on plant health. They are very motile and mobile, moving through soil and plants. As they travel, they cause tremendous damage to the plants. Their feeding activity leads to necrosis and decay of roots. Root necrosis significantly affects the health of the affected crop. These nematodes’ activity reduces the yield of infested crops. Farmers need effective strategies to manage Pratylenchus infestations. Proper control measures can minimize the impact on plant health. Understanding their behavior is crucial for effective management.

Damage 

• Meloidogyne root-knot nematode is among the severe constraints of a large number of crops. They also cause root lesions that are an entry for any secondary pathogens that may originate from the rhizosphere. This acts as double root knot nematode damage and leads to decay and degradation of the roots disabling them from absorbing water and other nutrients.
  For this reason, plants exhibit poor vigor and slow growth, while yields are significantly affected. Confusing root rot nematode infestation symptoms with nutrient deficiency or other root diseases hinders proper management. Effective and appropriate management of infestations requires accurate symptom identification. Properly addressing the issue improves plant health and yield.

Impact on Specific Crops 

• Tomatoes: Identify plants infected with root rot nematodes by symptoms like root decay and degeneration, including black and dead spots on the roots. This infection commonly affects the roots, causing the plant’s health to deteriorate. Tomato plants may develop diseases that affect their health, leading to yellowing, wilting, shriveling, and stunted growth.
• It has a strangled root system that is unable to provide sufficient energy for fruit development, resulting in low quality and low productivity of the fruits. The economic effect of tomato viruses on tomato growers is huge since it also reduces the amount of high quality tomato fruits or tomatoes.
• Other Crops: Meanwhile, root rot nematodes also attack a diverse section of other crops such as potatoes, carrots, and cereals. In each case, the symptoms are similar: root rot disease, poor nutrient absorption, and the general decline of the health status of the plant.

Biological control of plant nematodes

Integrated, innovative, and sustainable control strategies for the management of root rot nematodes include cultural practices, resistant varieties, and biological control. Polyculture with non-host plants can further be used to minimize nematode pressure in the soils. On the same note, the cultivation of nematode-resistant plants can also offer some degree of protection against infestations. Organic biopesticides, including beneficial fungi and bacteria, can supplement nematodes’ feeding on root rot nematode. This approach sustains the environment compared to using conventional pesticides. Farmers need to understand how root rot nematodes cause significant damage.

Knowledge of nematode behavior helps prevent future destruction. Implementing organic biopesticides reduces reliance on harmful chemicals. Beneficial fungi and bacteria offer a natural solution to nematode control. Sustainable practices ensure long-term soil health and productivity. Educating farmers on these methods promotes environmental conservation. Effective nematode management leads to healthier crops and higher yields. Integrated pest management practices are essential for sustainable agriculture.

Banana plant Nematodes

Radopholus similis (commonly known as the burrowing nematode) is one of such important pest that greatly threatens banana cultivating countries in the world. These nematode infection in bananas can be very dangerous to the banana crops by damaging both the quantity and quality of the banana fruits making production ineffective.

Causes and Damage

Nematode symptoms in banana include attacking the parenchyma of the root system of the banana and setting up feeding sites from which they start tunneling through the roots as they feed. This burrowing activity leads to the lesion of the root system i. e. the area where new tissues do not develop and old tissues decay. 

Feeding and reproduction by these nematodes cause further expansion of these lesions to the extent that the whole root is diseased and affected by root rot. Water and nutrients for the plant will no longer be properly absorbed because its root system is greatly affected.

The root knot nematode damage caused by banana nematodes manifests in several ways:The damage caused by banana nematodes manifests in several ways: 

• Root Rot: Once the initial lesions are established they develop into root rot with masses of the root system decomposing and dying. It is a root rot that affects the root system and makes it weak and more vulnerable to current wind especially in areas where there are extreme weather conditions.
• Reduced Nutrient Uptake: As the damaged root system provides the plant with necessary nutrients and water, the supply amount increases massively. As a result, the plants will not have a balanced intake of nutrients and this will be in the form of chlorosis; yellowing of the leaves, poor plant growth and overall a general decline of the plant. 
• Reduced Plant Vigor: The banana plants’ health and vitality degrade with time as the nematode infection worsens. It affects both the quality and quantity of bananas in production making the crop produce very few and smaller bunches of bananas. 
• Economic Impact: The impact of banana nematode infestations on the economic conditions can be immense. Lastly, decreased revenue will translate into lowered income for banana farmers and the high cost of nematode management in terms of either nematicides or soil treatment resulting to increase losses.

Stem and Bulb plant Nematodes

Potato rot nematodes, Dithlenchus dipsaci, damage stems and bulbs of various plants. These nematodes are serious pest organisms affecting many crops. Root knot and needle nematodes are particularly harmful to potato crops. These pests also plague many other vegetables and ornamental plants. Nematodes cause serious damage to the crops they infest. Farmers and gardeners face significant threats from these harmful nematodes. Effective management strategies are crucial to control nematode infestations. Nematode infestations can lead to substantial crop losses. Implementing preventive measures helps protect crops from nematode damage. Understanding nematode behavior is key to effective pest control.

Biological control of plant nematodes

Stem and bulb nematodes begin the attack by infecting the plants through stomata and wounds. They enter the crop field and pass into the plant stems and bulbs, creating a feeding site. These secrete enzymes into plant cells to digest the plant matter. They later digest the plant matter they release through enzyme activity. This feeding leads to several damaging effects on the plants. The plants suffer stunted growth and weakened structural integrity. Nutrient uptake becomes severely impaired due to nematode feeding. Plant cells experience extensive damage and reduced functionality. Yield losses are significant due to nematode infestation.

• Swelling and Distortion: Some of the first symptoms of stem and bulb nematode infestation on banana crop include swelling and deformity of both plant organs. This manifests itself in potatoes by causing deformation of stems and tubers. Nematodes’ action affects the cell cycle and growth of cells: the dissolution of membranes causes cell swelling and cells’ counterproductive growth.
• Rotting of Stems and Bulbs: The nematodes continue to feed hence more destruction of the stems and bulbs as usually leading to rotting of the stems and bulbs. Deteriorating tissue present from nematode grazing habits enhances the development of fungal or bacterial rot initiated upon nematode feeding. Potatoes may even become affected with soft rot in the tubers and turn unfit for marketing.
• Wilting and Yellowing: Plants commonly infected by the disease also experience wilting and yellowing due to inadequate water or nutrient translocation. The wounded stems and bulbs are unable to transfer water and food effectively to the rest of the plant and gradually leading to the decline of the whole plants.

Reniform plant Nematodes

Reniform nematodes is an important soil borne pest which passes its field stage in the form of nematodes living in the soil and in the field stage in the form of nematode parasitic in the roots of the host plant. These Nematodes are named reniform because of their kidney shaped appearance. They are particularly harmful in the tropical regions where there is a high humidity factor that aids their survival and damage to a wide array of crops; among the crops that are affected by the bollworms is the cotton.

Symptoms and Damage

Reniform nematodes inflict considerable damage on cotton plants, which manifests in several ways:Reniform nematodes inflict considerable damage on cotton plants, which manifests in several ways:

• Stunted Growth: Stunted plant growth becomes one of the main causes of renal nematode infestations. While attacking these plants’ roots, and then feeding on these organs, nematodes disrupt the process of water and nutrient uptake of plants. This means that the plants are unable to receive the amount they need to facilitate their normal growth leading to smaller and weaker plants.
• Yellowing of Leaves: Most infected cottons have indicators of chlorosis where the leaves become yellow. This is due to the fact that the plant can no longer uptake and convey its nutrients to the various component parts of the plant as a result of the root knot nematode damage on the roots. It is normally at the basal or bottom leaves of the plant hence progressing gradually upwards as the infestation intensifies.
• Wilting: It is also possible to find cotton plants infected with reniform nematodes having their leaves wilted even if soil moisture was sufficient. The feeding effect of the nematodes leaves the plant with most of their roots damaged hence making them unproductive in their performance in terms of water uptake in the plant as well as the transport within this plant. This leads to leaves of the plant drying under heat stress or when water in the soil is required.

Xiphinema Plant Nematodes

Xiphinema spp., known as Dagger nematodes or Tylenchida nematodes, are vascular parasites capable of transmitting plant viruses. These nematodes have long, thin bodies and unique stylet structures. Their stylets have a tooth on one side and a hook on the other. They use the stylets to enter plant cells and suck the cell contents. Feeding on plant roots causes direct damage but is less dangerous. Their primary threat lies in harboring and transmitting various plant viruses. These viruses can be a significant menace to crops, impacting agricultural productivity.

Virus Transmission

Dagger nematodes are highly effective vectors for several economically damaging plant viruses. Their ability to transmit viruses arises from the preferred feeding method of these insects. Dagger is a stem-boring nematode that releases virus particles from an infected plant into the host feeding organ during feeding. The viruses are released by its particles into the saliva during feeding, following which the particles are transferred to new host plants.

False Root-Knot Plant Nematodes

Nacobbus aberrans, commonly known as false root-knot nematodes, is a member of plant-parasitic nematodes that show similar damages as Meloidogyne spp . However, different Nacobbus aberrans have some remarkable biological and life cycle properties that differentiate them. It is a bigger problem though in the agricultural regions in North and South America where they thrive in carrying out their parasitic activities on various significant products in the region.

Biological control of plant nematodes

The false root-knot nematode damages plants and affects almost all crop types by causing roots to develop galls. These galls differ from those caused by true root-knot nematodes in four ways. The galls are smaller and less organized compared to true root-knot nematode galls. They are not formed by true root-knot nematodes, distinguishing them further. The galls on roots indicate nematodes have found ideal feeding sites. Nematode infestation will significantly disrupt plant growth and development. The presence of galls is a strong sign of nematode activity. Infestation leads to compromised plant health and reduced yields. Effective management practices are necessary to control these nematodes.

Rice Stem Plant Nematodes

Rice stem nematodes, Ditylenchus angustus, significantly threaten rice in warm and humid climates. These nematodes cause extensive damage to rice plants. Their presence leads to stunted growth and substantial yield losses. Nematode infestations in rice farms can devastate the geo-eco system. They reduce rice production and can make rice farming nonviable. This impact poses serious social and economic hazards for affected regions. Effective management is essential to mitigate these threats.

Damage in Rice Production

Rice stem nematodes cause certain kinds of losses to a rice plant and the overall yield and quality of rice suffers as a result. The following are the primary ways in which these nematodes impact rice production:The following are the primary ways in which these nematodes impact rice production: 

• Stunted Growth: The most apparent effect on rice due to rice stem nematode is stunted growth of the stems. The parenchymatous tissues of the stem are engorged as the nematodes feeding within them disrupt the vascular system. This causes interruptions in the transport of water and other nutrients and thus hinders overall growth. Plants affected by insect pests are stunted and are less robust than the normal counterparts.
• Poor Grain Development: Intake behaviour of rice stem nematodes influences rice grain formation. Plants are affected by an infestation render few grains and the grains that are formed are poor filled and small in size. This reduces total grain weight and decreases marketable yield. The milling properties of grain for rice also determine the quality of the rice which reflects the values of the paying consumers.

The Need for Organic Nematode Treatment

Limitations of Chemical Control Methods
Nematicides are also organic and inorganic compounds that are used to control the infestation of nematodes in agricultural fields. However, their use comes with several significant drawbacks:However, their use comes with several significant drawbacks: 

• Environmental Harm: This form of chemicals can be very dangerous for the environment as it is the case with nematicides. They can disrupt soils and water sources to cause losses in ecosystems. There are other organisms such as the beneficial insects and the soil microbes as well as the organisms living in the aquatic ecosystems that might be affected by these chemicals.
•  Impact on Human Health: The use of chemical nematicides is dangerous both to the human environment. Occupational exposure may cause acute or chronic illnesses for the farm workers and the surrounding communities due to such harmful substances. Leaching from these into crops and other food sources can also harm consumers.
• Cost: The use of chemical nematicides however is very high and may be unrealistic for small-scale farmers. The cost of the purchase and application of such amounts of chemicals also increases the cost of production and thereby lowers the profits.

Biological Control of Nematodes

NEMA PRO
Listeriosis is a condition known to be controlled by beneficial nematodes known as NEMA PRO that is a commercial available product that specially targets harmful nematodes. 

These nematodes, from genera Steinernema and Heterorhabditis, are beneficial as they are entomopathogenic, parasitizing and killing pest nematodes. When applied, NEMA PRO nematodes hunt pest nematodes in the soil dynamically. They follow chemical trails released by pest nematodes to locate them. NEMA PRO’s effectiveness comes from the active search behavior of these beneficial nematodes. The life cycle of Steinernema and Heterorhabditis involves parasitizing pest nematodes. This parasitization effectively reduces pest nematode populations in treated areas. Applying NEMA PRO results in significant pest control benefits. Beneficial nematodes play a crucial role in sustainable agriculture practices.

These useful nematodes attack harmful ones until they find one to infect and destroy using their symbiotic intestinal bacteria. The bacteria, highly toxic to pest nematodes, multiply inside them, causing their death. The bacteria provide food for the second nematode, which also multiplies. The second nematode continues the infection process, attacking more pest nematodes. This symbiotic relationship ensures effective pest nematode control. Beneficial nematodes significantly reduce harmful nematode populations. This biological control method enhances sustainable pest management practices. Using beneficial nematodes helps protect crops from nematode damage. Farmers benefit from healthier, more productive crops. Effective nematode control improves overall soil health.

The advantages of using NEMA PRO include: 

•  Targeted Action: NEMA PRO nematodes have a high degree of host specificity that is targeted only to pest nematodes and do not harm other species or the environment.
• Safety: Considering that these nematodes are natural and not harmful to man, domestic animals and helpful insects such as wasps or bees; it is an environmentally friendly method of nematicides use replacement.
• Ease of Application: NEMA PRO can be applied using normal irrigation systems that are easily accessible to the farmers therefore, it is easily incorporated into normal crop management practices.
• Sustainability: Nematodes as Biopesticides are effective in promoting sustainable crop production by minimizing the use of chemical pesticides and instead, strengthening the natural pest control aspects of the soil.

 Purpureocillium lilacinum

 Paecilomyces lilacinus (a. k. a. Purpureocillium lilacinum) is an entomopathogenic fungus that serves as a biological control against plant-parasitic nematodes. This fungus eradicates nematodes by infecting and killing their eggs and juveniles in the soil, reducing nematode populations. As a biocontrol agent, PL establishes itself in infested soils as a fungal root endophyte. The fungus actively seeks out nematode eggs and juveniles within the soil. It enters the egg shell or juvenile cuticle and secretes enzymes. These enzymes infect and break down the nematode’s protective layer. The fungus’s activity significantly reduces nematode numbers in treated areas. Using PL as a biocontrol agent offers a sustainable pest management solution. Farmers benefit from reduced nematode damage in their crops. Effective nematode control improves overall crop health.

Key benefits of Purpureocillium lilacinum include:

• Effective Control: It is a very effective fungicide that has a broad spectrum of activity of various nematode species such as root-knot, cyst and reniform nematodes and this makes it an ideal candidate to be used for nematode management.
• Compatibility: The use of Purpureocillium lilacinum should be combined with other biological methods and integrated management techniques for a more effective and efficient control of nematodes.
• Environmental Safety: Unlike other substances, Purpureocillium lilacinum serves as a natural organism that is unlikely to be a threat to the environment, other biological organisms, and human beings. It does not deplete but enriches the soil ecosystem by selectively killing non-beneficial nematodes.

 Conclusion

 The identification of the various nematode species and the effect they have on crop plants will be important to ensure appropriate control plans and measures are implemented. Adoption of biological control methods would therefore decrease the use of synthetic chemicals which will considerably reduce the negative impacts of agriculture on the environment and on the soil.

References:

1. Jones, John T., et al. “Top 10 plant‐parasitic nematodes in molecular plant pathology.” Molecular plant pathology 14.9 (2013): 946-961.
2. Mesa-Valle, Concepción M., et al. “Global research on plant nematodes.” Agronomy 10.8 (2020): 1148.