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Information: key in the fight against blight

For many plant diseases, despite researchers' best efforts, a 'cure' may prove elusive. Meanwhile, farmers need to know about the latest control measures, and how and where to implement them. Accessing timely information can be a challenge in developing countries, but web-based communication tools are proving successful against some age-old enemies, including potato late blight.

A tale of two islands

Potatoes affected by late blight (CIP)
Potatoes affected by late blight

When the first symptoms appeared on their potato plants farmers, who had never experienced late blight, did not recognise the ominous signs of the disease. But within just a few days, many were facing the devastating loss of their entire potato crop. The fungus-like pathogen, Phytophthora infestans, spread rapidly through fields and across hillsides, encouraged by the cool damp weather and encountering only susceptible potato varieties. In a matter of weeks, the island's potato harvest was destroyed and smallholder farmers bore the brunt, many losing the main source of their livelihood.

Surprisingly perhaps this is not the story of Ireland in the mid-nineteenth century, but of Papua New Guinea in 2003. Almost two hundred years later, late blight continues to wreak havoc in potatoes, the world's fourth major crop, which is widely grown and consumed on all continents. Yet, despite being one of the most intensively studied plant diseases (plant pathology labs around the world have late blight research programme) the disease is still the most serious threat to the world's potatoes. And in the few corners of the world so far unaffected by the disease, its arrival heralds the same shocking destruction first seen outside its area of origin (Mexico's Toluca valley) in the 1840s.

An intertwined history

Plant pathology and potato late blight have an intertwined history stretching over 150 years. As the Irish potato famine took hold, scientists struggling to understand the disease finally made the connection between a pathogenic micro-organism and its effects, and the discipline of plant pathology was born. Over the years, development of a variety of control options have held potato late blight at bay, at times for many years. But the pathogen has fought back, evolving into more virulent strains that prove resistant to chemical intervention.

But fungicides are not the only option. "While we haven't found a definitive answer to potato late blight, we certainly do have some effective control measures," says Greg Forbes, researcher at the International Potato Center (CIP) in Lima, Peru. "Our current strategy includes an emphasis on exchange of knowledge and information, so that these control measures are available to the farmers who need them, when they need them."

A global initiative

Potato sellers in an Andean market (CIP)
Potato sellers in an Andean market

Forbes coordinates the Global Initiative on Late Blight (GILB), which he describes as a network of researchers, technology developers and agricultural knowledge agents that serves as a platform to exchange ideas and opinions, and facilitates communication and access to information. In practice, this involves making extensive information available via the GILB website, hosting online discussion fora, regular meetings of regional groups, and periodic international conferences. The focus is on developing countries, though researchers worldwide participate.

"Planting resistant varieties is one of the best ways to avoid damage by late blight," says Forbes. "Quite a few varieties are available, some with high levels of resistance." Recent research has shown that, in some of the most popular varieties, this resistance is stable and robust across different locations around the world. And now, as developing countries expand their potato production, Forbes sees a window of opportunity. "Variety change is easier in less developed economies. As markets become more specialised, the window closes. CIP and its partners are trying to facilitate participatory breeding and selection programmes to ensure that the best varieties are in place."

Fungicide use is the most widely used control method for potato late blight, but costs are high, and not only financial. Without clear guidance on application of chemicals, worried farmers often spray their crop too frequently or with higher dosages than necessary. Their health, and the environment, suffer. "We want to help farmers optimise fungicide use," explains Forbes. "Most resource-poor farmers lack knowledge about the 'what, when, how and how much' of fungicide spraying. Optimisation usually results in a reduction of fungicide used, or a greater disease control efficacy."

Scientists are continuing the battle against late blight in the lab. The molecular biology of the pathogen has recently come under scrutiny, and holds promise for new ways to control the disease in the future. But in the meantime, spreading the word on resistant varieties and optimum fungicide use may be enough to hold potato late blight in check.

Written by: Anne Moorhead

Date published: September 2005


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