Plant-parasitic nematodes are a major biotic factor limiting crop productivity and ultimately crop production. Besides inflicting direct losses in crop yields, plant-parasitic nematodes also play an important role in disease complexes involving other pathogens. The expression of damage in crop plants due to nematodes often goes unnoticed for want of diagnostic symptoms. The estimation of crop losses due to nematodes is also cumbersome, and precise techniques for the same still remain elusive. Nevertheless, several reports are available on this aspect; the most widely quoted is the one by Sasser and Freckman [1]. According to them, plant-parasitic nematodes cause on an average 12.3% losses annually in 40 major crops at a global level; the losses are more in developing countries (14.6%) than in developed nations (8.8%). Based on this comprehensive survey on a global scale, the annual economic crop yield losses due to plant-parasitic nematodes in major crops have been estimated to be USD 173 billion [2].

All India Coordinated Research Project (AICRP) on Nematodes is a discipline-oriented project that aims to develop nematode management technologies for economically important nematodes in major crops through multi-locational trials in different agro-climatic regions of India. Under the aegis of this project, loss estimations due to nematodes in different crops are a continuous program operating at 18 centers of the project across the country. Field trials on loss estimations employing t tests are conducted regularly in various crops in different seasons using nematicidal product (carbofuran) at varying initial nematode populations (> economic threshold level). The details of methodology employed for conducting loss estimation trials under AICRP (Nematodes) are available in [3]. The enormous data generated under this program have been compiled in a technical bulletin [4]. Expression of crop losses in monetary terms is essential for project formulations and helps in showcasing, convincing and seeking research support from policy planners. This exercise has to be done periodically to offset the inherent aberrations due to temporal parameters such as crop production, areas under crop production and fluctuations in minimum support price (MSP).

The information generated up to 2004–2005 under the aegis of AICRP on Nematodes has been compiled previously [5]. According to this, the yield losses in 24 different crops amounted to Rs. 21,068.73 million annually; rice alone suffered losses to the extent of Rs. 4779 million. We have attempted to update the information on current basis, and the same is presented in this note.

Data on area, production, yield of principal crops, and MSP of various agricultural commodities have been obtained from most reliable sources [6,7,8]. Barring a few crops such as ginger, turmeric [9], sunflower [10] and papaya [11], the data generated by AICRP on Nematodes have been used for assessment of yield losses. Loss estimations varied for each crop according to locations, seasons and years; therefore, data obtained from different centers were averaged for calculations. Out of total area for a particular crop, only 10% has been considered as nematode infested and the same has been used for calculations of yield losses.

A perusal of data presented in Table 1 reveals that overall economic losses in 30 crops amount to Rs. 102,039.79 million annually; the losses in 19 horticultural crops were assessed at Rs. 50,224.98 million, while for 11 field crops it was estimated at Rs. 51,814.81 million. The mean percent losses were higher in horticultural crops, i.e., 23.03% (fruits 25.5%, vegetables 19.6%, spices 29.5%) than in field crops, i.e., 18.23% (cereals 18.8%, pulses 23%, oilseeds 11.8%, fiber crops 19.75%). The economic losses in rice due to rice root-knot nematode, Meloidogyne graminicola, alone were maximum (Rs. 23,272.32 million) among all the crops and nematodes considered. In wheat, avoidable losses due to cereal cyst nematode, Heterodera avenae, in Rajasthan and Haryana (the major molya disease affected states) were calculated at Rs. 8967.52 million. Wheat seed gall nematode, Anguina tritici, has been excluded from this study, since it has already been eradicated from Punjab, Haryana and western UP and only sporadic incidences are reported from other wheat growing areas of the country. Citrus (Rs. 9828.22 million), banana (Rs. 9710.46 million) among fruit crops; and tomato (Rs. 6035.2 million), brinjal (Rs. 3499.12 million) and okra (2480.86 million) among the vegetable crops suffered comparatively more losses that is partly attributable to areas of production in respect of these crops. Potato cyst nematode, Globodera rostochiensis and Globodera pallida are restricted but widespread in the Nilgiri Hills of south India. As per current information, potato crop is grown in about 1440 ha in the Nilgiris [12] and the same has been considered for loss assessment that amounts to Rs. 127.04 million.

Table 1 Estimated losses due to economically important plant-parasitic nematodes to various crop in India (2014–2015)
Full size table

It is clearly discernible from the data in Table 1 that root-knot nematodes (Meloidogyne spp.) alone are responsible for Rs. 77,373.87 million losses in different crops that constitutes about 75.83% of the total estimated losses, thus proving to be the economically most important of all the plant-parasitic nematodes.

Some more interesting facts can be deduced when this data as compared with that reported earlier [5]. First is an overall increase of 4.84 times in economic losses since 2007 that is attributable to escalation in MSP, increase in area under cultivation, and additional crops included in the study, etc. Second is the emergence of M. graminicola as most important and national problem of rice relegating Aphelenchoides besseyi, Ditylenchus angustus and Hirschmanniella spp.; however, A. besseyi is certainly important in some states (Assam, West Bengal, Odisha, Madhya Pradesh, Gujarat and Chhattisgarh). Third is a relatively more shift toward horticulture, and therefore, nematode problems in these cropping systems.

It is emphasized here that the figures presented in this note pertain to quantitative losses only. The qualitative losses such as forking in carrots, infection in underground edible plant parts like tubers in potato, rhizomes in turmeric, ginger, etc., often result in non-acceptability of produce at the level of consumers; such parameters have not been taken into account while assessing losses due to nematodes. Furthermore, the information on nutritional quality parameters in crop produce due to nematodes is totally lacking. Nevertheless, the information compiled and presented in this paper would serve as an important tool to consider research investments for public/private sectors vis-à-vis monetary losses. Besides, private sector engaged in production of chemical and biological products for nematode management may find it useful for planning appropriate inputs in different crops and areas.

The methods employed for estimation of crop losses due to pests and diseases in general, and plant-parasitic nematodes in particular, are often subjected to criticism for want of precision. The debate on role of “other pests and pathogens” prevalent under field conditions (other than the target pest) is justified. However, the product used in treated plots (carbofuran in this case) is most appropriate for the purpose where only target nematode is the major pest (hot spot for nematode). The impact of other pests and diseases is uniform across the treated and untreated plots. Conducting such trials in “closed environments” involving only the target pest may be unrealistic because the nematode effects are liable to be influenced by prevailing biotic and abiotic stresses under field conditions.

This note depicts significance of plant-parasitic nematodes in Indian agriculture. In a recent report, the annual overall losses to crops considering all pests and diseases in India were projected at Rs. 500 billion [13]; the relative proportion attributable to plant-parasitic nematodes as per this study amounts to approximately 20.4 percent that is fairly accurate assessment. Further, in a recent feedback from various centers of AICRP (Nematodes) in India, the adoption rate of nematode management technologies is meager 28 percent. Considering the overall losses projected in this study (Rs. 102,039.79 million = USD 1.58 billion), the monetary benefits accrued by adoption of nematode management technologies work out to Rs. 28,571.14 million. The information generated through this study will help in focusing on nematodes as a serious constraint in Indian agriculture scenario, as well as to fix research priorities.