Barley mild mosaic virus

Barley mild mosaic virus (BaMMV) is a significant viral pathogen within the Bymovirus genus of the Potyviridae family. It primarily infects winter barley, causing stunted growth and substantial yield losses in temperate regions across the world.

The primary symptoms include light green or yellow mosaics, stripes, and mottling on the leaves, usually visible during the early spring. Infected plants exhibit severe dwarfing, reduced tillering, and an overall loss of vigor, which prevents them from reaching full physiological maturity.

The biological cycle of BaMMV is unique as it is soil-borne, transmitted by the plasmodiophorid fungus Polymyxa graminis. The virus persists in the resting spores of the fungus within the soil, allowing it to survive for many years even in the absence of a host crop.

The spread of the disease is favored by cool and wet conditions during the autumn, which align with the winter barley planting season. The infection process begins when the motile zoospores of the fungus infect the roots of the young barley seedlings, injecting the virus directly into the host cells.

Managing BaMMV relies heavily on the use of resistant barley varieties, which is the most sustainable approach. Cultural practices such as adjusting sowing dates and employing proper crop rotation help reduce the pressure of Polymyxa graminis, although complete eradication from infested fields is extremely difficult.