Monday, 24 September 2018
There are over 100 varieties of Fusarium spp. with symptoms varying greatly according to host and pathogen species. Some symptoms commonly seen include yellowing of lower leaves, wilting, leaf chlorosis and vein clearing, stunted growth and red to brown discolouration of vascular tissue. Stem or cutting rot (but not always) appear as a soft, mushy rot at the base of a cutting or rooted plant, frequently with a purplish-reddish margin.
Sometimes bright red, globular fruiting bodies may form on stem bases in the case of advanced infection. Leaf spots often appear on immature leaves, are irregularly-shaped and tan-reddish brown in colour, sometimes surrounded by a chlorotic halo. Under wet conditions, creamy orange spore masses may be produced in lesions. Bulb rots often start at wounds or through cuts formed at harvest. The basal plate, scales and roots become brown-black, and the rot is generally dry and firm. Foliage turns yellow or brown and dies prematurely.
Many Fusarium spp. are host specific so check symptoms to the host to determine infection.
Fusarium spp. are a soil-borne fungal disease that can persist in infected soils or on decaying roots for long periods due to the production of resilient chlamydospores. Rain and irrigation water splash, or wind and/or insects (e.g. fungus gnats etc.) can disperse the pathogen short distances. Infested soil, dust, soil-less mixtures, trays/pots and cutting knives are common sources of inoculum. Long distance spread of Fusarium spp. can occur via movement of infested seed, seedling plugs, rooted cuttings and other plant material.
Fusarium wilts are usually most severe under warm conditions, but some host specific strains are favoured by cooler temperatures. Prolonged wet humid conditions encourage sporulation on infected tissue and promotes infection of stems and leaves. Stem rot of cuttings commonly occur during mist propagation.
Several varieties or races of Fusarium are host specific, but most Fusarium spp. affect a very wide range of crops. These include several fruit and vegetable crops such as lettuce, beans, grape, onion, garlic, shallots, curcubits, asparagus, banana, passionfruit, and strawberry. Also, many ornamental crops such as Dianthus, Callistephus, Chrysanthemum, Cyclamen, Dahlia, Delphinium, Euphorbia, Gerbera, Gladiolus, Hibiscus, Iris, Narcissus, Rhododendron, Rosa, Viola are affected by some form of Fusarium.
An initiative of the Nursery Levy funded National Nursery Industry Biosecurity Program (NY15004) and ‘Building the resilience and on-farm biosecurity capacity of the Australian production nursery industry’ Project (NY15002).