''Botrytis fabae'' is a plant pathogen, a

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

that causes chocolate spot disease of broad or fava bean plants, ''

Vicia faba ''Vicia faba'', commonly known as the broad bean, fava bean, or faba bean, is a species of vetch, a flowering plant in the pea and bean family Fabaceae. It is widely cultivated as a crop for human consumption, and also as a cover crop. Variet ...

''. It was described scientifically by Mexican-born Galician microbiologist

Juan Rodríguez Sardiña ''Juan'' is a given name, the Spanish and Manx versions of ''John''. It is very common in Spain and in other Spanish-speaking communities around the world and in the Philippines, and also (pronounced differently) in the Isle of Man. In Spanish, t ...

in 1929.

Symptoms

Chocolate spot disease caused by ''Botrytis fabae'' manifests itself as small red-brown spots on

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

, stems and

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

s of broad bean plants. These enlarge and develop a grey, dead centre with a reddish-brown margin.

Spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s form on the dead tissue and spread the infection to other plants. In severe infections leaves and flowers may fall and badly affected stems may keel over.Government of Western Australia

Life cycle

The pathogen survives as

sclerotia A sclerotium (; (), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favor ...

in the soil or on crop stubble and residues. It can also be introduced by the use of infected seed. The sclerotia germinate and condiophores are formed, the conidia (asexual spores) are dispersed by air currents and deposited by rain on susceptible young plants. When the conidia

germinate Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...

, small

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

s are formed on previously healthy leaves. As the crop grows and within four or five days of infection, conidiophores are produced and secondary inoculum is produced. The conidia are liberated from dead or dying leaves and flowers, usually those that have fallen to the ground, and are spread to other plants in the vicinity by wind and splashes of water. This secondary spread of infection proceeds most rapidly under cool, humid conditions, the optimum conditions being a temperature between 15 °C and 22 °C and a relative humidity of at least 90%.Department of Primary Industries, Victoria, Australia
/ref> Under dry conditions the pathogen remains within the limits of the chocolate-coloured spots but under wet conditions the lesions expands aggressively. Alternating wet and dry conditions may lead to spots with a series of concentric growth rings, however during longer periods of wet weather the fungus thrives and the leaf is killed.Royal Horticultural Society
/ref> After harvest the fungus remains in a semi-dormant state in plant debris until the next growing season. Infected seed may be stored with healthy seed and infect a new crop.

Control

Infection can be minimised by the destruction of plant debris at the end of the season, the avoidance of sites recently used for faba bean crops and the selection of cultivars with a high level of resistance to the disease. Fungicides can be used but for best results the crop should be carefully monitored, the pathogen should be accurately identified and the crop sprayed with the correct product at the optimum time. The greatest impact of chocolate spot disease is through the loss of flowers and spraying during the flowering period is likely to achieve the greatest increase in yield.

Distribution

The fungus is widely distributed, having been reported from south-east Asia, Australia,

Northeast Africa Northeast Africa, or ''Northeastern Africa'' or Northern East Africa as it was known in the past, is a geographic regional term used to refer to the countries of Africa situated in and around the Red Sea. The region is intermediate between North ...

and

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

, Europe, the Middle East, North America, and South America.

References

{{Taxonbar, from=Q10433893 Fungi described in 1929 Fungi of Africa Fungi of Asia Fungi of Australia Fungi of Europe Fungi of North America Fungi of South America Fungal plant pathogens and diseases Sclerotiniaceae