Fusarium Head Blight of Barley: A Plant Pathologist's Perspective

Andy Tekauz. Agriculture and Agri Food Canada, Winnipeg, Manitoba, Canada. Presented at the 1999 Canadian Barley Symposium and reprinted from the Proceedings with permisssion.

Abstract
Fusarium head blight (FHB) is the most important disease of barley in Manitoba, Canada. This also applies to Minnesota and North Dakota, making FHB of regional and international concern. Since FHB was practically absent in barley as recently as five years ago, its current predominance here represents an extraordinary transformation. The contemporary 'epidemic' of FHB in cereal crops in Manitoba, and which now may include parts of Saskatchewan and Alberta, can be traced to 1984, That year, two grain samples of wheat from the southern Red River Valley were found to contain 'tombstone' kernels and detectable levels of 'vomitoxin' -both are diagnostic for FH13 (Clear and Ambramson, 1986). Today, these 'symptoms' are usually referred to as 'FDK' (fusarium damaged kernels), and 'DON' (deoxynivalenol). Systematic field surveys for FHB in cereal crops in Manitoba were initiated in 1986 and have continued since. The results are published annually in the Canadian Plant Disease Survey. It is intriguing that while FHB has been detected in wheat, since 1984, it wasn't observed in barley until 1993, and did not occur at appreciable levels until 1994. In 1998, after only five years, FH13 was found in every barley field surveyed in Manitoba and damage was as high as in wheat. Clearly, barley initially was not the favored host for the FH13 pathogen, but now is as vulnerable as wheat. This may reflect a fundamental change in the pathogen population, or in the conditions promoting development of disease. Fusarium head blight affects cereal crops in several ways. Infection results in small or thin, shriveled and discolored kernels replacing normal ones. The smallest infected kernels usually are lost during harvest, contributing to yield reduction. Others retained in the grain may contain DON, toxic to humans and livestock at higher concentrations, and contribute to grade/quality loss as FDK. Such kernels, and those otherwise normal in appearance but infested by Fusarium, if subsequently used as seed, may fail to germinate or the germinated seedlings may not emerge from soil (Gilbert and Tekauz, 1995). Furthermore, the integrity and reputation of the region and its crops will be compromised. The effects of FHB are additive and, during severe epidemics, can be devastating. Because FHB was essentially a 'new' disease to barley in Western Canada, it presented a unique opportunity to deploy the range of disciplines comprising 'plant pathology.' These include: epidemiology, mycology, symptom expression, inoculation and rating protocols, host reaction, resistance sources (and crossing of these into adapted cultivars), biotechnology, surveys and disease management. More often, pathologists' research has a narrow focus, and the chance to employ a broad approach is seldom presented. Much of the research on FHB done in Western Canada in the past 10 years was made possible by support from the Western Grains Research Foundation. This support has been both timely and visionary, as it began ca. 1988, FHB's 'early years.' A brief summary of findings relating to FHB in barley follows.
Keywords: Fusarium Fusarium head blight DON Deoxynivalenol vomitoxin  

Sintesis