Glucose found to play a major role in blight on Valencia peanut

Valencia peanut plants growing in a field in Clovis, New Mexico

The fungus Sclerotinia sclerotiorum is a pathogen that attacks a wide range of food and non-food crops. The fungus causes a disease called Sclerotinia — a blight that rapidly rots various parts of the plant, including the fruit. Normally, this fungus has a white cottony appearance when growing on food sources containing a mixture of potato and agar under laboratory conditions. However, the fungus was shown to have a dark colour when it was sampled from Valencia peanut in eastern New Mexico and western Texas.

Read this paper in the Canadian Journal of Plant Science.

Sclerotinia sclerotiorum fungus showing a black structure called sclerotium, which allows the fungus to survive in the soil for many years. Two cup-like structures (brownish) called apothecia are visible on the sclerotium. The apothecia will produce spores which are carried by wind onto peanut plants for infection.

In a previous study, the dark colour in the fungus was suppressed by using a compound that prevents the production of melanin, a pigment responsible for dark colouration. The dark-coloured fungus was able to cause disease in Valencia peanuts, whereas the fungus in which the melanin was suppressed was not able to cause the disease.

The current study was conducted to further evaluate the differences between the dark-coloured fungus containing melanin and the lighter-coloured one that had melanin production suppressed.

The fungus with the dark-coloured variant was found to cause disease because it produces a compound called oxalic acid that allows the fungus to infect the peanut plant, and oxalic acid was not produced by the fungus in which melanin production was suppressed. However, when grown on food sources containing the compound glucose, oxalic acid was produced by the fungus that had melanin production suppressed, and the fungus was able to cause disease in peanut plants.

This study indicates that the compound glucose plays a major role in the production of oxalic acid and in the ability of S. sclerotiorum to cause disease in Valencia peanut.

Read the full paper — The role of carbon sources in relation to pathogenicity of Sclerotinia sclerotiorum on Valencia peanut by Phillip Lujan, Barry Dungan, Omar Holguin, Soum Sanogo, Naveen Puppala, and Jennifer Randall.