Spot blotch is a barley disease caused by a fungus called Bipolaris sorokiniana. This disease impacts barley grown in locations with higher humidity and moderate temperatures. Under epidemic conditions, it can cause serious losses to barley yield due to decreased photosynthesis in leaves that have been compromised by spots. As spots grow in size, they eventually join together, which results in complete blockage of nutrients reaching the leaf tips. This impact is most severe when the fungus reaches the upper plant canopy, which is critical for maximizing the capture of sunshine that plants use for ‘food’. As a result, barley kernels are not filled completely which reduces the plumpness of harvested kernels.
Farmers get paid by the weight of their barley, so thinner kernels equate to a thinner wallet. More importantly, spot blotch can result in crops being downgraded from malt barley to feed barley, thereby losing out on valuable cash premiums.
Infected kernels impact the quality of malt and result in lowered malt extract (the amount of alcohol that can be produced per unit of malt), altered protein content, and non-uniform kernel germination. The fungus can also produce off-flavours that are highly undesirable in malt-based beverages, such as beer.
Pesticides are available to control the fungus, but they are costly to barley farmers and are not considered a sustainable farming practice due to potential impacts on the environment. In Canada, scientists have worked very hard over the past few decades to develop malting barley varieties that can naturally fight off the spot blotch-producing pathogen.
In the current study, scientists studied 200 different types of barley, primarily adapted to be grown in the Canadian environment. These were tested in Manitoba and Saskatchewan within disease nurseries. Scientists used biotechnological tools (gene chips) to find specific genetic markers associated with disease resistance. The best Canadian barley varieties were found to carry gene versions (alleles) that made them spot blotch resistant. These markers were part of what has been previously termed the Midwest Six-rowed Durable Resistant Haplotypes (MSDRH) found at certain locations within their genome (on chromosomes 1H, 3H, and 7H). It turns out, that the 3H allele of the genome was underrepresented in Canadian barley and thus future resistance can be enhanced to continue the fight against spot blotch. They also found other helpful markers on chromosomes 1H, 2H, and 4H that could be used in breeding spot blotch resistant barley.
Genome-wide association study of adult plant resistance to spot blotch in an elite Canadian two-row barley germplasm collection
TITLE IMAGE: Spot blotch is a barley leaf disease
