''Botryosphaeria obtusa'' is a

plant pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

that causes frogeye

leaf spot A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions ...

black rot Black rot is a name used for various diseases of cultivated plants caused by fungi or bacteria, producing dark brown discoloration and decay in the leaves of fruit and vegetables: * A disease of the apple, pear and quince caused by a fungus ('' Botr ...

and

canker A plant canker is a small area of dead tissue, which grows slowly, often over years. Some cankers are of only minor consequence, but others are ultimately lethal and therefore can have major economic implications for agriculture and horticultur ...

s on many plant species. On the leaf it is referred to as frogeye leaf spot; this phase typically affects tree and shrubs. In fruit such as the

apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...

cranberry Cranberries are a group of evergreen dwarf shrubs or trailing vines in the subgenus ''Oxycoccus'' of the genus ''Vaccinium''. In Britain, cranberry may refer to the native species ''Vaccinium oxycoccos'', while in North America, cranberry ...

and

quince The quince (; ''Cydonia oblonga'') is the sole member of the genus ''Cydonia'' in the Malinae subtribe (which also contains apples and pears, among other fruits) of the Rosaceae family (biology), family. It is a deciduous tree that bears hard ...

, it is referred to as black rot, and in twigs and trunks it causes cankers.

Symptoms

Black rot ''Botryosphaeria obtusa'' enters the fruit through wounds. These can be made by insects, birds or growth cracks. At first a brown spot, near the calyx, appears on the fruit. The spot on the fruit then enlarges and black/brown rings appear on the fruit. The fruit holds its shape, however, unlike other fruit diseases. The fruit will then wither up and can remain on the tree for another year before falling off. During this time

pycnidia A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inve ...

appear on the surface of the rotted fruit. Frogeye leaf spot In

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 ...

the fungus begins by causing purple specks on infected leaves. These then enlarge to cause large spots on the leaf, developing a brown color. The spots appear to have rings of brown with a purple margin, thus giving it its frogeye appearance. The spots can then produce pycnidia which can separate this species of fungus from other possible leaf fungi. Canker On twigs, branches and trunks ''B. obtusa'' can infect where there has been a winter injury or fire blight cankers. Slightly sunken reddish/brown spots appear on the infected areas of bark. These then enlarge to form cankers, which can then enlarge slightly more each year. The bark usually dies and can, after time, be pulled away from the tree. In older cankers the pycnidia appear on the bark. Black dead arm disease of grapevine ''Botryosphaeria obtusa'' is the pathogen of black dead arm disease of

grapevine ''Vitis'' (grapevine) is a genus of 79 accepted species of vining plants in the flowering plant family Vitaceae. The genus is made up of species predominantly from the Northern Hemisphere. It is economically important as the source of grapes, b ...

. It has been shown to be able to oxidise wood δ-

resveratrol Resveratrol (3,5,4′-trihydroxy-''trans''-stilbene) is a stilbenoid, a type of natural phenol, and a phytoalexin produced by several plants in response to injury or when the plant is under attack by pathogens, such as bacteria or fungi. Sources ...

into

delta-viniferin δ-Viniferin is a resveratrol dehydrodimer. It is an isomer of epsilon-viniferin. It can be isolated from stressed grapevine (''Vitis vinifera'') leaves. It is also found in plant cell cultures and wine. It can also be found in ''Rheum maximowicz ...

.Identification of phytotoxins from Botryosphaeria obtusa, a pathogen of black dead arm disease of grapevine. Jules Désiré Djoukeng, Suzanna Polli, Philippe Larignon and Eliane Abou-Mansour, European Journal of Plant Pathology, Volume 124, Number 2, pages 303-308,

Treatment and control

The most effective treatment is to

prune A prune is a dried plum, most commonly from the European plum (''Prunus domestica''). Not all plum species or varieties can be dried into prunes. A prune is the firm-fleshed fruit (plum) of ''Prunus domestica'' varieties that have a high solu ...

out the infected areas on trees, to ensure transfer between trees does not occur. Fruit that is infected can stay on the tree for over a year, and therefore remaining fruit should be removed to avoid another source of inoculation for other trees. The trimmed branches or dead fruit should then be burned or disposed of immediately as the organism can survive on the dead tissue for a long period of time. Infection of leaves and fruit can be avoided by spraying them with a

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

. The treatment for the fungicide should be also kept up to date via the manufacturer's instructions.

References

External links

USDA ARS Fungal Database

Invasive.org - Image Gallery
{{Taxonbar, from=Q4948840 obtusa Fungi described in 1832 Fungal plant pathogens and diseases Apple tree diseases Grapevine trunk diseases Eudicot diseases Taxa named by Lewis David de Schweinitz