Biological warfare: Combating the new wheat rust disease

A veritable battlefield exists on the fields as the wheat crop faced by as many as fifty biological threats.

Besides poor policies for storage and marketing at harvesting, wheat production is constrained by many biotic and abiotic factors. Among biotic factors insects, pests and diseases are a significant threat that reduce the yield and grain quality. While no significant occurrence and damage by insect pests is reported nevertheless wheat crop is damaged by more than fifty diseases of fungal, viral, plant parasitic nematode, bacterial, phytoplasmal and parasitic higher plant origin.

Among all diseases rusts are widespread in almost all wheat growing areas of the country. The rusts damaging the wheat are leaf or orange rust, black stem rust, and yellow or stripe rust and differ from each other on the mode of infection and pathogen type. However, these days a new wheat disease Ug99 stem rust is putting the farmers and researchers across the country on high alert. Recently it has been predicted by United State Department of Agriculture, Foreign Agricultural Service that the disease could reach Pakistan within two to three years since its discovery in Iran in March 2008. Still the disease has not been detected in country‘s 2008-09 wheat crop.

The new wheat rust strain (Puccinia graminis) of this unbeaten champion Ug99 started its journey from Uganda since its discovery in 1999 and then has spread throughout Kenya and Ethiopia and after crossing the Red Sea has reached Iran. And 19 per cent of global wheat is produced and grown in the migration path of this new rust strain, and if this entire zone comes under attack then we are looking the destruction of millions of tones of grains worth billions of dollars. This can potentially cause a global famine and threatens the future food security in our country.

Moreover, the pathogen of this disease produces clouds of fungal spores which number in the billions and can blow hundreds of miles in the wind and if conditions are favourable to the disease then it can destroy 50-70 per cent of the wheat crop in an area. It attacks the above-ground part of plants and unlike other strains, can cause 100% crop loss. And the mode of fungus spores invasion is also interesting in that the spores permeate through the plant stomata from where gases exchange takes place from the atmosphere, and pierce its tentacles like haustoria into the wheat’s cells and extract nutrients from these infectious cells.

Although disease spread can be prevented by growing resistant wheat varieties but still limited success has been achieved against this wheat rust. Conventional breeding for resistant varieties has been said to be the best method and research activity to prevent the crop from diseases in the long-term. But the cultivated bread wheat which is mostly grown for yield has a limited gene pool and it is difficult to find the genes with variation to such an extent that may offer resistance.

And the only way forward for researchers when a new fungal strain triumphs over the resistant genes is to find wild relatives so that can be introduced to the new one by cross breeding. Therefore researchers are trying out to explore how this fungus rust invades the plant cells so that they might be able to engineer resistant proteins from wild relatives. Switching to genetic engineering can unravel the problem of incorporating large chromosome segments that reduce yield along with the resistant genes.

Researchers are using the flax plant and its rust as a model with their focus on the substances secreted by the rust before it gets entrance to host cells in the hope of controlling their metabolism - substances that plant would be able to recognise as the first signs of the rust and once any success is worked out it will enable bioengineers to identify and transmit effective resistant genes. And certainly such an advance would bring success in the war against rusts.

The time is now, to take steps and continue efforts by the researchers, agricultural research institutes like Parc to develop wheat varieties resistance to the deadly disease. The government should allocate a separate budget for the National Wheat Breeding Programme to work on this new rust strain which is a threat to the domestic wheat crop. The researcher should get training from the international institute to fight with this challenge. Breeding strategies such as a DNA-marker assisted selection should be practiced to incorporate diverse genetic resistance to Ug99. Because of socioeconomic implications of stem rust on food security alternative crops and livelihood systems should also be taken into account. The seed multiplication agencies such as Punjab Seed Corporation and local organisations should be encouraged to produce commercial seed of newly developed stem rust resistant varieties with the condition that farmers and other stakeholders play a leading role. This role will include supporting of breeding programmes, the maintenance and multiplication of breeders and ensuring that foundation seed and commercial seed is readily available to farmers; and on-farm demonstrations of selected varieties should be done.

The current infrastructure should be strengthened by restoration of greenhouses and essential field facilities; pathology and molecular laboratories, irrigation systems should be upgraded and communications capacity, especially internet and transport facilities should be improved.

The agricultural extension department should launch a campaign among the farming community to raise and maintain awareness of the wheat stem rust problem. And the campaign should also  advise farmers to adopt management strategies in case of other types of rusts such as avoiding late and thick wheat sowing, excessive nitrogenous fertilisers and possibly apply light irrigation with long intervals. They should treat their seeds with chemicals several times to protect their crops. The disease mostly spreads and occurs by growing susceptible cultivar; therefore the cultivation of such varieties should be discouraged. These strategies can help to lessen the rust incidence and keep us on track in fight against hunger in the country.

Published in The Express Tribune, February 21^st, 2011.