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Real-Time Quantitative RT-PCR of Defense-Associated Gene Transcripts of Rhizoctonia solani-Infected Bean Seedlings in Response to Inoculation with a Nonpathogenic Binucleate Rhizoctonia Isolate

First, second, and fourth authors: Plant Science Department, Macdonald Campus of McGill University, 21111 Lakeshore Rd., Sainte-Anne-de-Bellevue, Québec, H9X 3V9, Canada; and third author: Institut de Recherche en Biologie Végétale, Université de Montréal, and Jardin Botanique de Montréal, 4101, rue Sherbrooke est, Montréal, Québec, H1X 2B2, Canada

Certain isolates of nonpathogenic binucleate Rhizoctonia spp. (np-BNR) are effective biocontrol agents against seedling root rot and damping-off. Inoculation of bean seed with np-BNR strain 232-CG at sowing reduced disease symptoms in bean (Phaseolus vulgaris) seedlings caused by R. solani. Molecular analyses of the spatial expression of three defense-associated genes were carried out using real-time quantitative reverse transcription-polymerase chain reaction (QRT-PCR) assays. This method allowed accurate quantitative evaluation of transcript levels of pG101 encoding for 1,3-β-D-glucanase, gPAL1 encoding for phenylalanine ammonia lyase, and CHS17 encoding for chalcone synthase in 1- and 2-week-old bean seedlings that were inoculated simultaneously with np-BNR and infected with R. solani, and in seedlings that were singly inoculated with either fungi or not inoculated. In the seedlings that were infected with R. solani only, results revealed that, following infection, activation of all defense-associated gene transcripts was achieved with significant increases ranging from 7- to 40-fold greater than the control, depending on the defense gene and tissue analyzed. Seedlings that were treated with np-BNR and infected with R. solani had expression similar to those that were treated with np-BNR only, but the levels were significantly down-regulated compared with those that were infected with R. solani only. These findings indicate that disease suppression by np-BNR isolate is not correlated to pG101, gPAL1, and CHS17 gene activation.

Additional keywords: biological control , induced systemic resistance , plant defense response .