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Transgenically Enhanced Expression of Indole-3-Acetic Acid Confers Hypervirulence to Plant Pathogens

June 2002 , Volume 92 , Number  6
Pages  590 - 596

Barry A. Cohen , Ziva Amsellem , Rudy Maor , Amir Sharon , and Jonathan Gressel

First, second, and fifth authors: Department of Plant Sciences, Weizmann Institute of Science, Rehovot IL-76100, Israel; and third and fourth authors: Department of Plant Sciences, Tel Aviv University, IL-69978 Tel Aviv, Israel

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Accepted for publication 14 January 2002.

Fusarium oxysporum and F. arthrosporioides, pathogenic on Orobanche aegyptiaca, were transformed with two genes of the indole-3-acetamide (IAM) pathway leading to indole-3-acetic acid (IAA) to attempt to enhance virulence. Transgenic F. oxysporum lines containing both the tryptophan-2-monooxyngenase (iaaM) and indole-3-acetamide hydrolase (iaaH) genes produced significantly more IAA than the wild type. IAM accumulated in culture extracts of F. oxysporum containing iaaM alone. F. arthrosporioides containing only iaaM accumulated IAM and an unidentified indole. Some transformants of F. oxysporum expressing only the iaaM gene also produced more IAA than the wild type. Sub-threshold levels (that barely infect Orobanche) of transgenic F. oxysporum expressing both genes and of F. arthrosporioides expressing iaaM were more effective in suppressing the number and size of Orobanche shoots than the wild type on tomato plants grown in soil mixed with Orobanche seed. Stimulating an auxin imbalance enhanced pathogen virulence by affecting the host in a manner similar to low doses of auxin herbicides such as 2,4-dichlorophenoxy acetic acid.

Additional keywords: formulation, polymerase chain reaction, transformation.

© 2002 The American Phytopathological Society