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A chemical that South American frogs excrete from their skin could protect potatoes and other crops from a range of diseases, according to biotechnologists in Canada.

Researchers at the University of Victoria inserted a modified frog gene into potato plants to make them produce the chemical.

The genetically modified (GM) potatoes showed resistance to infection by a broad range of disease-causing fungi and bacteria, including those responsible for diseases such as dry rot, late blight and pink rot.

Different species of frog produce different sets of chemicals, including some called dermaseptins, from their skin depending on the environment they inhabit. The chemicals help protect frogs from bacteria and other 'pathogens'.

The most potent dermaseptin, known as B1, has been isolated from the skin of tree frogs called Phyllomedusa bicolor that live in the rainforests of South America, where the hot and humid conditions mean fungi and bacteria thrive.

The Canadian team showed that a synthetic version of dermaseptin B1 inhibited the growth of "an exceptionally broad range" of fungi that cause plant diseases, as well as the bacterium Erwinia carotovora, which causes blackleg in potato plants in the field and soft rot of tubers in storage.

The researchers genetically modified potatoes to produce the chemical and exposed the GM plants to the same organisms. The inserted gene gave "unusually broad-spectrum and powerful resistance to infection", according to the team's research, which the journal Theoretical and Applied Genetics published online in June.

Santosh Misra, who led the work, told SciDev.Net the approach could help farmers in developing countries to reduce pesticide use, increase yields and reduce losses of crops stored after harvest.

Fungal and bacterial infections can cause heavy losses of potato crops. The standard approach has, in recent decades, been to spray crops with pesticides, but this can be damaging to the environment and farmers' health, and encourages the fungi and bacteria to develop pesticide-resistance.

Misra's team says that because their GM potatoes could resist so many types of disease-causing organism, the same gene could be used to protect other crops such as wheat, barley and sugar.

The researchers say that the preliminary results of studies to show the safety of dermaseptin B1 "are positive". They add that the GM plants showed no ill effects of having been genetically modified.

Eric Messens, professor of plant molecular genetics at Flanders Interuniversity Institute for Biotechnology at Ghent University, Belgium, says the research into the safety of GM crop using genes that produce toxins should precede the main research, not follow it.

Messons told SciDev.Net that it was important to test if dermaseptin B1 is toxic to people and animals, as well as study whether the chemical gets broken down or builds up in the body.

"Long-term effects must be taken into consideration because even though the authors claim that the amount of dermaseptin is low, the accumulation effect can not be ignored," said Messons.

For example, said Messons, long-term consumption of peas called Lathyrus sativus can cause paralysis if a toxin in the peas accumulates in people, as has happened in Bangladesh and India.

Messons suggests that safety could be improved by ensuring that GM potatoes only produce dermaseptin B1 when they become infected, and then only in the skin of the potato, which could then be removed by peeling.

Genetic modification of potato against microbial diseases: in vitro and in planta activity of a dermaseptin B1 derivative, MsrA2
Milan Osusky, Lubica Osuska, William Kay and Santosh Misra
Department of Biochemistry and Microbiology, University of Victoria, Victoria, B.C., V8W 3P6, Canada
Received: 30 November 2004 Accepted: 25 April 2005 Published online: 10 June 2005

Abstract
Dermaseptin B1 is a potent cationic antimicrobial peptide found in skin secretions of the arboreal frog Phyllomedusa bicolor. A synthetic derivative of dermaseptin B1, MsrA2 (N-Met-dermaseptin B1), elicited strong antimicrobial activities against various phytopathogenic fungi and bacteria in vitro. To assess its potential for plant protection, MsrA2 was expressed at low levels (1–5 mgr

g/g of fresh tissue) in the transgenic potato (Solanum tuberosum L.) cv. Desiree. Stringent challenges of these transgenic potato plants with a variety of highly virulent fungal phytopathogens—Alternaria, Cercospora, Fusarium, Phytophthora, Pythium, Rhizoctonia and Verticillium species—and with the bacterial pathogen Erwinia carotovora demonstrated that the plants had an unusually broad-spectrum and powerful resistance to infection. MsrA2 profoundly protected both plants and tubers from diseases such as late blight, dry rot and pink rot and markedly extended the storage life of tubers. Due to these properties in planta, MsrA2 is proposed as an ideal antimicrobial peptide candidate to significantly increase resistance to phytopathogens and improve quality in a variety of crops worldwide with the potential to obviate fungicides and facilitate storage under difficult conditions.