BENZOTHIADIAZOLE ACTIVATES SYSTEMIC ACQUIRED RESISTANCE GENE EXPRESSION AND DISEASE RESISTANCE IN BARLEY
Y TOKUNAGA1, JPR KEON2 and JA HARGREAVES2
1UBE Industries Ltd, 1978-5 Kogushi, Ube, Yamaguchi, Japan; 2IACR-Long Ashton Research Station, University of Bristol, Long Ashton, Bristol BS18 9AF, UK
Background and objectives
Systemic acquired resistance is an inducible defence mechanism in plants that has the potential to provide broad-spectrum and long-lasting disease control. The recent finding that the plant defence activator benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) induces acquired resistance and the accumulation of defence-related gene transcripts in wheat  has attracted a great deal of interest in this form of resistance for controlling cereal diseases. In this study, we examine the relationship between defence-related gene activation in BTH-treated barley seedlings and resistance against powdery mildew (Erysiphe graminis f. sp. hordei).
Materials and methods
2-week-old barley (cv. Golden Promise) seedlings (growth stage 1.5) were treated with a range of concentrations of BTH (Bion, CGA245704, Novartis). The compound, formulated as water-soluble granules (50% a.i.), was suspended in water and sprayed onto plants until run-off. Leaves were harvested at appropriate time intervals after treatment and total RNA prepared for transcripts analysis. Defence-related genes, including leaf-specific thionins and lipoxygenase, were monitored following BTH treatment by reverse transcription PCR and/or by Northern blot analysis. For disease assessment tests, plants were inoculated with E. graminis spores 3 days after treatment with BTH, and disease symptoms (percentage infected leaf area) were assessed 7 days later.
Results and conclusions
BTH was found to induce the accumulation of two barley defence-related gene transcripts at low rates of application and very soon after treatment. One of these induced resistance genes encoded a methyl jasmonate-inducible lipoxygenase which was detected using a DNA probe recovered by reverse-transcription PCR using oligonucleotide primers based on the known gene sequence (GeneBank accession number U56406). The other gene encoded leaf-specific thionin  and was identified using cloned cDNA (pHvDB4, a gift from Dr H Bohlmann) as a hybridization probe. Treatment of barley seedlings with BTH led to ca 43% reduction in disease symptoms, and reduced disease severity was correlated to the appearance of defence gene transcripts.
1. Ryals J, Kessmann H et al., 1996. Plant Cell 8, 629-643.
2. Bohlmann H, Apel K, 1987. Molecular and General Genetics 207, 446-454.