The Hindu Business Line : Popular wheat strain faces threat from rust fungus

Under attack
Rust pathogens cause yield losses of up to 20-39 per cent in wheat.
78S84 race is similar to `Yr-27 virulence' that hit Pakistain's crop in recent times.
The Yr-9 resistance gene in PBW-343 protected the variety against yellow rust attacks.
Now, the fungus is making a re-appearance in the form of 78S84.

New Delhi , Sept. 17

The country's most widely grown wheat variety, PBW-343, is facing threat from a new race of yellow rust fungus.

The origin of this virulent strain, called `78S84', is not known, but scientists confirm its occurrence and the potential damage posed to PBW-343, which is cultivated in over six million hectares or roughly 80 per cent of the wheat area of Punjab, Haryana and western Uttar Pradesh.

"We first detected the new race in 2001 and this year particularly on PBW-343 in many fields. Right now, it seems to be occurring late in the season towards end-March and so the infestation is low. The problem could be worse if it strikes in February or early-March and we have to be prepared for this in the next two years," said Dr Arun Kumar Sharma, Principal Scientist (Crop Protection) at the Directorate of Wheat Research, Karnal (DWR).

Back in new forms

In case of early stage infestation, rust pathogens are known to cause yield losses of up to 20-30 per cent in wheat. PBW-343's newfound susceptibility to the `78S84' race is similar to the `Yr-27 virulence' yellow rust epidemic that has hit Pakistan's workhorse wheat variety, Inquilab-91, in recent times.

All this is indicative of the fact that yellow rust, which was said to be a tale of the past, is back in the sub-continent in new virulent forms.

When it was introduced in 1995, PBW-343 was seen to confer resistance to a deadly `46S119' race of yellow rust, which came into India via Iran, Afghanistan and Pakistan during the early nineties.

The Yr-9 resistance gene in PBW-343 protected the variety against yellow rust attacks throughout the decade and after.

But now, the fungus is making a re-appearance in the form of `78S84'.

New variety

The good news, however, is that the DWR has come out with a new variety, DWR-17, which is claimed to be resistant to the new rust race.

"It has shown resistance to 78S84 at the adult plant stage and also gives 1.2 quintals per hectare more grain than PBW-343. This should be good enough for the short-term, though we need to breed resistance at the seedling stage as well," noted Dr Jag Shoran, Principal Scientist (Crop Improvement) at DWR.

DWR-17, slated for commercial release next month, may over time replace PBW-343 as the most prolific wheat variety.

Black rust

Meanwhile, there is a new black rust pathotype, `Ug99', first identified in Uganda and spreading in east Africa towards the sub-continent. Most wheat varieties in India are said to be susceptible to this race, as they all contain the `Sr-31' gene on which it is virulent.

"We have not found this race yet anywhere in the country. But we have already in place Ug99 resistant genetic stocks that can be deployed against any potential threat," Dr Sharma added.