Nematode management in spices: The key issues

It is no secret that spices are important components of many global cuisines and cultures, making them highly marketable. India produces, consumes, and exports the most spices. Spices rank third in terms of value in the agricultural export basket after marine products and rice. However, compared to other crops, they only occupy 2.3% of the GCA (gross cropped area). Among the 65 notified spices, cumin, chilli, and coriander occupy the largest amount of land, but these same three have experienced the highest levels of abuse when it comes to pesticide use (43%). 

Crops in this sector are afflicted by a range of problems, but one of them is nematodes! These worms eat plant roots, resulting in reduced crop yields and inferior quality. Root knot nematodes (RKNs), which are generally widespread and particularly hard to eliminate, may wreak extensive crop damage and even endanger the food supply. Burrowing nematode (Radopholus similis) is a nematode that is more localised in its distribution, but which can still create significant harm. Lesion nematodes (Pratylenchus spp.), one of the most significant nematode problems in ginger and turmeric production nowadays, have become increasingly difficult to control. These pests are difficult to detect and contain numerous symptoms in addition to their common nematode species. As a result, it is difficult to accurately identify and combat them. In addition, a fungal infection can result from the plants’ predisposition to disease, which complicates treatment procedures.

We take a look at the problems caused by nematodes in crop production systems as well as why they are so damaging to spice crops in this blog post. We will discuss some technological alternatives that might help reduce nematode danger in crop production systems, as well as some measures farmers and policy makers can take to handle this issue properly.

Nematode Control in Spices – A Challenging Task

If you’re a spice grower, nematode management is a tricky task. It is a challenging task due to the complex interactions between nematodes, fungi and viruses. Integrated pest management (IPM) strategies like crop rotation, amendment of soil with organic material, use of resistant varieties and biocontrol agents are widely employed for reducing damage caused by nematodes. Chemical control with synthetic nematicides is generally used as a last resort but is often not effective due to rapid development of resistance in nematode populations. These unique ecosystems are often perennial, with many spices being vegetatively propagated. It can be hard to diagnose nematode-related problems, and crop rotation or soil solarisation may not be feasible. To keep your crop safe, repeated applications of pesticide may be necessary – an ongoing battle against pests that could get out of hand if left unchecked.

Vegetative propagation: Crops such as black pepper, cardamom, ginger, turmeric and all the tree spices are vegetatively propagated through clonal propagation. However, this will accelerate spread of endogenous pathogens. It will lead to reduced genetic diversity which makes plants vulnerable to pests and diseases. Additionally, it also results in modified root architecture favourable for nematodes and crowding of uniform planting materials which further reinforces the spread of pests and diseases. Therefore, it is important to develop novel forms of crop propagation in these crops in order to reduce the risk posed by them.

Perennial crops: It is important for growers to understand the unique ecological niche that perennials require in order to protect their plants from nematode damage. In order for perennials to thrive, they must have a combination of high humidity, high temperature, high rainfall and dense vegetation present in the soil. A presence of multiple hosts in close proximity can further increase the population of nematodes and pose an even greater threat. 

Diagnosis is not easy: The effects of nematode damage are often not visible until the later stages when it is too late to take corrective measures. This makes it all the more important for growers to be aware of these conditions and take preventive steps such as crop rotation or addition of beneficial organisms that can help keep a check on the population build-up.

Non availability of pesticides/resistant lines: To make matters worse, there is no curative measure in place for spices; none of the available nematicides have  label claims for spices, there are no Maximum Residue Levels (MRLs) and a majority of the recommended nematicides have been removed. Additionally, use of appropriate pesticides should also be employed if necessary under proper guidance from an expert consultant or agriculture department personnel. On the other hand, the availability of nematode resistant lines remains inadequate; only a few root-knot nematode resistant or tolerant lines exist and not one against migratory endoparasites.

Biological control yet to take off: The potential of biological control for the protection of spices has been growing over the past decade. This can be seen through the introduction of novel delivery systems and formulations, many of which have been patented by research institutes. In nurseries, biological control measures are usually quite successful. However, in plantations there is more uncertainty with varying results from application to application and repeated applications needed over time due to the challenge posed by humid tropical environments. 

We need new strategies

The plague of plant-destroying nematodes has been an ongoing battle between farmers and the pests for centuries. As agricultural technologies become more advanced, the fight against nematodes must evolve as well.

Thrust to be on production of nematode-free planting materials: Our strategy should focus on creating spice nurseries that can produce healthy, nematode-free plantlets. Up front, it is necessary to prevent nematode damage in spices by implementing best practices in nurseries. This includes preventing the spread of nematodes during large-scale multiplication processes as well as introducing resistant/tolerant plant lines through genetic manipulation techniques. This will lead to healthier plantations, with the following advantages: less pesticide use due to the reduced need for pest control; efficient pesticide delivery; minimal pesticide contamination; and a lower nematode load. To further ensure successful and sustainable plantations, we must also identify gaps in our current processes such as introducing soil-less propagation methods, improved fumigation methods and nursery certification. We must also conserve fragile ecosystems that are home to these spices by avoiding activities that could destabilise the environment or soil and water resources during control measures. 

Need for effective bioagents: To make spice protection more effective in plantation environments, better strains need to be developed that offer a stable formulae and efficient delivery systems. A new approach may be to take advantage of spectrum of green molecules produced by either plants or microorganisms that could then be scaled up as novel nematicides – a concept yet to be explored fully but worthy of further consideration from pesticide companies, instead of relying on harsh chemicals that are damaging to both crops and ecosystems alike. 

Introduce Hi-tech technologies: One such strategy is to use precision agriculture and AI-based tools for diagnosis and mapping of nematode populations. This would allow farmers to accurately identify areas with high concentrations of pests, enabling them to apply targeted treatments instead of blanket applications that harm not just the crop but also the environment.

Use of genomics tools: Another potential solution is gene silencing and gene editing technologies which allow us to precisely modify a crop’s genetic makeup in order to confer resistance against certain pest species. Already there have been a few successful experiments that have demonstrated potential success when it comes to combating plant-destroying pests through genetic engineering techniques – although public opinion on GM crops may need more time before they become widely accepted by society at large. 

Importance of Sustainable Agriculture

As the focus shifts away from conventional farming methods of IPM and INM, sustainable agriculture has become the mantra in the spice industry today. Whether it’s by importing countries calling the shots or by exporters launching initiatives such as Sustainable Spice Initiative and IndGAP for spices, it’s clear that something needs to be done to benefit both farmers and consumers. Climate change and deteriorating ecosystems pose a huge threat to spice cultivation, so initiatives such as these are more important than ever. Now, traceability is being insisted upon in order for spice producers to move ahead of COO (Country of Origin). Single-origin farms have started becoming more common too! Sustainable agricultural models are essential for keeping pace with global demand for quality spices while also protecting our environment and ecosystems. We must continue pushing forward with initiatives that prioritise sustainability in all aspects of the spice industry so we can reap the rewards now and long into the future!

However, successful spice management is not only about prevention but also requires a participatory approach with all stakeholders involved in the effort: farmers should be informed about pest issues while research institutions should provide up-to-date technologies; finally, industry players need to ensure adequate remuneration for farmers via strong supply chains. Lastly, policy changes such as nursery certification standards, label claims related to pest problems or food safety regulations need to be considered at all times when addressing pest issues related to spices production. 

Conclusion

In conclusion, much progress has been made over recent years in terms of finding new ways to combat plant pests including those caused by nematodes. As technology advances further still, so too will our ability combat these insidious invaders – leading us towards a future where spice cultivation will be much safer from deadly infestations!

[Invited talk presented in the National Conference on Plant Parasitic Nematodes, 16-18 January 2023, Bengaluru, India organised by Bayer CropScience Ltd.]