A plethora of viruses as well as insect vectors and pests pose an emerging threat to the tomato belt of Maharashtra; it is a wake-up call to stakeholders to adopt good agricultural practices
Currently, as the second wave of the novel coronavirus disease (COVID-19) continues across India, the tomato virus is back, wreaking havoc in Ahmednagar, Satara, Nashik and Pune districts of Maharashtra.
Farmers have alleged their otherwise red, juicy tomatoes have turned into yellow and spongy, plastic-textured fruits. This, despite their adopting the recommended guidelines of testing seeds and pest control provided by the public and private sectors.
In June last year, multiple viruses had attacked tomato crops in this region. Samples examined from Satara and Ahmednagar were found to be infected with Cucumber Mosaic Virus (CMV), Groundnut Bud Necrosis Virus (GBNV) and Tomato Chlorosis Virus.
“One of the factors for the extensive spread could be a change in climate and cultivation time,” the Indian Institute of Horticultural Research-Bengaluru had maintained.
Viral diseases are a serious threat to profitable tomato cultivation. In the absence of any recognised or recommended antiviral products, management strategies chiefly rely on genetic resistance, hygienic practices or the eradication of diseased crops to prevent virus spread.
The ever-increasing international trade in seeds and fruits has enhanced the risks manifold. Coupled with the changing climate, the consequent spread of invasive viruses and their associated insect vectors is a potential threat.
People, profession and profit
Maharashtra farmers start growing the summer tomato crop in February and the first harvest commences from late April and continues to cater to the market demand till July. Last year, farmers in the Pune, Satara, Ahmednagar and Nashik districts compalined of early ripening and substantial yield loss.
Hyperactive media house made it viral news. This problem propped up again this year in the Rabi tomato crop. Rabi is the most preferred season in these irrigated areas, often dominated by tomato hybrids (more than 90 per cent). It meets export demand, which is essential for realising maximum profit and thus filling the pockets of peasants.
The past decade has witnessed spectacular hybrid seed-driven growth in vegetables, which has almost doubled within three-four years (from 2016 to 2019). In the past three years, tomato hybrids have come to account for almost a 10 per cent share of total vegetable seed values. The major players in seed sales in India are Syngenta India Pvt Ltd, Bayer Crop Science AG, BASF SE, East West Seed Company, UPL Ltd (Advanta Seeds) and others.
About 1,000 acres of area has been affected by this malady in the Narayangaon belt itself. This belt lies in Junnar, Pune. A case study on price fluctuation in the last five months carried out in Narayangaon mandi revealed the crashing of the tomato price to Rs 2 to Rs 3 per kg. Obviously, tomato farmers prefer to throw the produce on the roads, rather than harvest and sell.
Indian Agricultural Research Institute-Regional Station, Pune (IARI-RS, Pune) tested a few samples of virus-infested tomato from the Kolwadi and Alandi areas of Pune district last year. Viruses including CMV, GBNV, Tomato Mosaic Virus, Pepper Mottle Virus and Potato Virus Y were detected.
This year, virologists of the station tested samples from affected areas collected in the second fortnight of May. Five viruses were detected: CMV, Groundnut Necrosis Virus or GBNC, Capsicum Chlorosis Virus, PVX or Potato Virus Y and the Poty virus group.
In recent years, several viral diseases, including Tomato Leaf Curl Virus or ToLCV, Pepino Mosaic Virus and Tomato Brown Rugose Fruit Virus have emerged in greenhouses and open cultivated tomato crops and are presently impacting fresh-market tomato production worldwide.
Two major strains (New Delhi and Bangalore) exist in case of ToLCV, causing leaf curling in tomato plants. Viruses may undergo alteration to inhabit in a newly-introduced niche. The CMV is also an increasing threat to tomato plants.
Tomato Brown Rugose Fruit Virus (ToBRFV) is considered as “the pandemic of the tomato” globally. Till date, this virus has not been not reported / detected in India. But, it is high time to be alert and accelerate our efforts to detect it and take precautionary measures.
The Federation of Seed Industry of India (FSII) wrote to the advisor and director (plant protection), Government of India. It requested the declaration of India as free from specified pathogens for ToBRFV. The FSII asked for this as quarantine requirement for the export of capsicum and tomato seeds to the United States and European Union.
In our last article for Down To Earth, we had anticipated this virus. The reports of EPPO (European and Mediterranean Plant Protection Organization) recorded ToBRFV-contaminated seeds in tomato and chili from India being imported to Italy and the Czech Republic.
This virus was categorised as a quarantine pathogen by EPPO in November 2019. Obviously, many countries might have not done the same in their quarantine system. The virus first emerged in Israel in 2014.
It has spread subsequently to fields and greenhouses across West Asia, Europe, Mexico, North America, China and other parts of the world. ToBRFV transmits mostly by people and equipment coming in contact with plants and also by wind or insects and can survive for years together in soil.
The highly transmittable ToBRFV poses a serious threat to tomato in India. As of now, we are not sure of its presence. However, disease symptoms of ToBRFV including deformation, uneven ripening, yellow / brown spotting / blotching and rugosity, which are also caused by other tomato viruses, were observed in fields in the last two years.
Sap-sucking insect aphids, whiteflies and thrips spread many virulent viruses to crops. Cultivation practices are continually changing in India. In Maharashtra in particular, more acreage is being dedicated to protected (polyhouse) cultivation.
This has led to intensified insecticidal treatments, often unilateral and injudicious pesticide utilisation as advised by pesticide dealers and agro-consultants. International trade and travel has compounded the vector problem, with new species, strains / biotypes / genetic groups emerging.
Many of the viruses transmitted by aphids stay in stylets (mouthparts) of the insects for a short span and their short probe / feeding is sufficient to spread the disease. This makes most of the insecticidal treatments useless.
However, though private companies conduct several training programmes for tomato farmers in affected areas, they seldom cite this cause. Their primary motto is maximising business. It is high time farmers recognise this hard fact.
The reason behind the suggestion of planting tall barrier crops like maize around the tomato crop is based on some science. The aphid vectors landing on barrier plants lose their viral load from their stylets, before they move on to target the tomato crop. IARI-RS, Pune, Pune as well as IIHR-Bengaluru advocate barrier crops.
Maharashtra is witnessing emerging threats in the form of the Solanum whitefly (Aleurothrixus trachoides) in tomatoes, potatoes and bell peppers and an exotic whitefly (Paraleyrodes minei) infestation in several fruit tree crops. Clearly, climate change is causing the shifting of the pest spectrum. This demands more research.
There is no cure for viral diseases. Hence, prevention is the best policy. Seed-borne viruses must be given due attention. Quality seeds from reputed sources must be procured. Resistant / tolerant varieties must be adopted if available.
Unfortunately, the recent cases of multiple virus invasions make the task more difficult to get resistant / tolerant stock. We must revisit the possibility of seed-borne mode of viruses in tomato viruses like CMV.
Scientists and policy makers must make efforts to inform the public, in particular farmers, about tomato viruses. We suggest conducting suitable surveys and surveillance at regular intervals.
We suggest appropriate funding in multl-institutional project mode to multi-disciplinary scientists stationed in Maharashtra state to bridge the research gap. Local conventional varieties, botanicals and bio-pesticides and adjusting of planting time should be given due priority in insect vector management.
Plant growth regulators and hormones only improve plant immunity, but are not a panacea for viruses. The virus syndrome seems to be showing season-specific recurrence in the region. The relationship between viruses and temperature and rainfall (humidity) must be adequately understood by concerted researches.
We also suggest:
Farmers must return to their local / conventional varieties, with good agricultural practices (GAP), for at least two-three seasons in endemic areas. GAP essentially includes the records of crop practices, dates of plant protection applications undertaken with reliable and approved reasons.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.