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

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

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. Vari ...

''. It was described scientifically by Mexican-born Galician microbiologist Juan Rodríguez Sardiña in 1929.

Symptoms

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

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

, stems and

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

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 reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

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 (; : sclerotia () 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 u ...

in the soil or on crop stubble and residues. It can also be introduced by the use of infected seed. The sclerotia germinate and conidiophores 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 flowering plant, angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the sp ...

, small

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

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. 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, encompasses the countries of Africa situated in and around the Red Sea. The region is intermediate between North Africa and East Africa, and encompasses ...

and

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

, 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 Fungus species