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Abstract
Leptosphaeria maculans causes blackleg disease of canola (Brassica napus L.). Bacteria isolated from soil, canola stubble and plant parts were assayed for suppression of blackleg. In plate assays, the bacteria isolated from canola stubble had the highest agar-diffusible antifungal activity (75%), which was fungitoxic. In plant cotyledon assays, endophytes had the highest disease suppression. Bacteria with the highest disease suppression in cotyledon assays also had significant disease suppression at the three- to four-leaf stage. PCR screening for bacterial biosynthetic genes, commonly thought to be involved in plant disease suppression, revealed 22 bacteria to be positive for pyrrolnitrin. Pseudomonas chlororaphis and P. aurantiaca isolates contained the phenazine biosynthetic gene. Three Bacillus cereus isolates had the zmaR resistance gene. This study generated a novel set of primers specific to the zwittermicin A biosynthetic cluster. The PCR screening has confirmed the presence of genes encoding pyrrolnitrin (55%), phenazine (10%), zwittermicin A biosynthesis (7.5%) and zwittermicin A resistance (7.5%) from the canola phyllosphere and rhizosphere, which seems more widely distributed than genes for 2,4-diacetylphloroglucinol and pyoluteorin.
Acknowledgments
We thank the Natural Sciences and Engineering Research Council for funding this project. We are very thankful to Dr Linda Thomashow, Dr Joyce Loper, Dr Caroline Press and Dr Jo Handelsman for their help in providing bacteria, to be used as positive controls, and some primers for the PCR-screening. The technical support of Paula Parks is greatly appreciated. We are also very thankful to Dr Teresa De Kievit for proof reading this manuscript and for the valuable suggestions.