Historical Information on Karnal Bunt

Dubin has worked on small grains diseases for the past 21 years and was previously posted as Regional Pathologist/Breeder for South Asia, based in Nepal.

Based on recent emails and questions it is obvious and correct that scientists are concerned about the potential spread of KB in the USA and whether it can establish and cause significant damage in the principal wheat growing areas.

I think that we can give some information based on empirical and anecdotal evidence over many years in the Indian sub-continent that may be of use. But first, it is very important to say that epidemiological research has been insufficient and thus the data to make informed conclusions are inadequate. It is imperative to fund in depth research on KB with special emphasis on epidemiology and control, especially resistance. Further, we must differentiate the effects of KB related to quality and yield loss and quarantine considerations.

KB appears to have caused significant quality or yield damage in areas that are ecologically similar to its place of origin in Karnal, India, i.e., it seems narrowly adapted. These are areas such as Punjab, western Uttar Pradesh, Haryana, in India; northern plains of Pakistan: parts of Afghanistan; and parts of northwestern Mexico. They are where spring wheats are planted in the fall, the winters are mild with rain or high humidity at flowering, and the crop is highly fertilized and irrigated. Observations over the years have failed to show its importance in eastern or southern India, Bangladesh or the Nepal terai. These are areas that are similar but hotter than the traditional KB areas. Seed from the northern areas of India have moved south for decades without causing disease, as far as is known. Similarly, seed has moved to the mountains without reported occurrences.

In relation to resistance KB was historically important, at times, on the old tall cultivars that apparently had little resistance. With the advent of the semi-dwarf wheats the two cultivars that covered large hectarage, Sonalika and Kalyansona were modestly resistant and the disease was not considered particularly important. However, when one high yielding but highly susceptible cultivar, WL711, was released (1979) it subsequently covered large hectarage in the north of India, and within several years KB became epidemic in these areas. When the KB problem became more acute the researchers responded and moderately resistant cultivars were released over the last decade or so. KB has, once again, became of less concern. Besides release of highly susceptible cultivars, the crop ecology changed with the coming of the semi-dwarfs, increased irrigation, denser canopies, and higher fertilizer use may have contributed to the KB increase in the absence of resistance. Concerted breeding efforts in India and Mexico have produced high yielding, resistant cultivars in both countries.

The above are historical observations and the behavior of the pathogen could, of course, change.

From the point of view of quality and yield loss KB has not been one of the most important wheat diseases. The quarantine considerations are certainly quite different.