Fusarium is a group of soil-borne fungi with many different species. Fusarium is widespread and can infect a range of host crops. Many species are considered weak pathogens and can only infect wounded or stressed host plants.
Life cycle and appearance of Fusarium head blight or scab
Most Fusarium species only make asexual spores. Some also produce ascospores. In general, most Fusarium specieshave a similar life cycle. Fusarium overwinters for many years in the soil and on crop residues of infected plants as chlamydospores (thick walled mycelium cells) or mycelium. Survival is also possible on seed, greenhouse structures, tools and machinery. Primary infection is either seed-borne or takes place as infection of the roots at the root tip or in small wounds, for example where lateral roots branch off from the tap root.
Gibberella zeae (Fusarium graminearum) overwinters as chlamydospores and ascospores in crop residues. Primary infection is from this inoculum or from infected seed. Infected seed doesn’t germinate well and seedlings die, causing irregular crop density. The foot of the plant is infected, either because the seedling was infected or by direct infection of the foot by overwintering inoculum. On the infected foot, conidia are produced that further spread the disease. Gibberella zeae (Fusarium graminearum)primarily infects the older, lower leaves. The spores are dispersed upwards to the ears by splashing rain drops or wind. On the infected ears, the typical pink spores are produced which may further spread the disease. Ascospores of Gibberella zeae (Fusarium graminearum)germinate at temperatures between 4 and 35 °C, with an optimum between 25 and 28 °C. Germination only occurs at relative humidity (RH) above 80%. Warm (25-30 °C) and humid (RH above 85%) conditions increase chances of infection.
Fusarium fungi cause vascular wilt, root rot, foot and stem rot, leaf lesions, fruit rot, fusarium head blight in cereals, such as wheat (fusarium head blight wheat) and post-harvest decay.