( ded that the spread of P. infestans may...)Researchers find gene that may be at root of potato blight

P. infestans belongs to a group of destructive pathogens called oomycetes. Oomycetes aren't easy to categorize ?although they physically look like fungi, on a molecular level they more closely resemble algae.

Over the last 75 years, potato breeders have introduced at least a dozen late blight-resistant genes into the cultivated potato. The researchers looked at one of these genes, R3a.

Kamoun and his colleagues thought that if a potato plant contained R3a, that it could detect P. infestans manifestation by recognizing Avr3a and then ward off an impending disease. The R3a gene was discovered earlier this year by scientists at Wageningen University, The Netherlands.

In laboratory experiments on leaves from potato plants, the scientists found that the leaves containing the R3a gene successfully resisted late blight infection when exposed to P. infestans races that carried the Avr3a gene. However, some races of P. infestans with mutations in their Avr3a gene escaped the resistance response triggered by R3a.

Further laboratory analysis showed that when R3a detected Avr3a in a leaf cell, that plant cell died.

"This programmed cell death is how the plant keeps the pathogen from spreading to other cells," Kamoun said. "Only a few cells die. It's one mechanism of defense some plants have."

Until now, researchers knew little about P. infestans on the molecular level.

By studying Avr3a, R3a and similar genes, researchers may be able to determine what happens during the earliest stages of late blight infection.

"This study is a big step forward in late blight research," Kamoun said. "Current strategies for managing late blight in potato and tomato crops are unsustainable and costly. In the United States and other developed countries, the chronic use of chemicals to mana
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Source:Ohio State University