The study was conducted to evaluate the potential of induced resistance to infestation of sunflower (Helianthus annuus L.) by the parasitic weed Orobanche cumana Wallr. Treatment of sunflower seeds with 40 ppm of benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) for 36 h completely prevented infection in root chambers. In pot studies using 2.86 x 10(-4) g of Orobanche seeds per gram of soil as inoculum, the total number of O. cumana shoots was reduced by 84 and 95% in the 60-ppm BTH treatment in the first and second trial, respectively. Evaluation of the disease incidences revealed that attachment of O. cumana at the sunflower root and the stage of early penetration was reduced in the BTH-treated plants. Chemical analysis of root extracts revealed synthesis of the phytoalexin scopoletin and of hydrogen peroxide in the BTH-treated sunflower roots, but no increase in lignification. Western blot analysis demonstrated accumulation of the pathogenesis-related protein chitinase in roots and stems of induced resistant plants. These results show that the phenomenon of induced resistance is not restricted to viral, bacterial, and fungal disease and demonstrate the great potential of this protection strategy as an effective component of future plant production systems.

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Nitrogen (N) fertilization and fungicide applications are still subject to discussion concerning the influence on Fusarium head blight (FHB) and related mycotoxin accumulation. Field studies were made in 2000-2001 and 2001-2002 to investigate the effect of two N-rates and 11 plant protection treatments on FHB severity and the content of FHB-related mycotoxins, namely deoxynivalenol (DON) and zearalenone (ZEA) under conditions of natural infection. The treatments applied can be summarized as (i) an integrated approach using a decision support system, (ii) the use of two plant strengtheners, Bion Ò (benzo [1,2,3]thiadiazole-7-carbothioic acid S-methyl-ester, BTH) and a compound based on the biomass of the cyanobacterium Spirulina platensis, (iii) the use of plant strengtheners in combination with a broad-spectrum fungicide and (iv) common fungicide strategies against foliar diseases. Fusarium infections as well as the analysed mycotoxins were observed at low levels in both years. Disease severity was significantly increased by conventional N-fertilization only in 2001. Neither FHB severity nor mycotoxin accumulation was significantly influenced by any of the treatments, although treatments without fungicides appeared to lead to lower disease severities. In 2002, there was a tendency towards higher disease severities when common fungicide strategies were applied. Mycotoxin contamination was found in grain samples from both years. In 2001 DON was mainly traceable, whereas in 2002 ZEA was also detected. Mycotoxin contamination was influenced by N-fertilization rather than by the treatments. In 2001, the DON content was significantly increased due to the conventional N-supply. Our results indicate that less intensive fungicide strategies, including plant strengtheners, are no worse than common fungicide strategies under conditions of low FHB severity and mycotoxin accumulation. Immoderate N-fertilization however, can increase mycotoxin levels significantly even under conditions unfavourable for Fusarium spp.www.blackwell-synergy.com

The systemic acquired resistance (SAR) was studied in barley to find out specific molecular markers for this type of resistance. Such markers may serve as diagnostic tools to indicate the defense‐status of a plant and, additionally, may be used to identify new resistance‐inducing compounds in broad screening experiments. Upon treatment of barley leaves with the resistance‐inducing compound 2,6‐dichloroisomicotinic acid (INA) we found, in addition to a yet unidentified basic protein of 45 kDa (designated BIR‐1) induction of a specific 6kDa polypeptide. Using Northern‐and Western blot analysis this small polypeptide was identified as JIP‐6, a known member of the jasmonate‐induced protein (JIP)‐family of barley that was previously demonstrated to be a leaf thionin (ANDRESEN et al. 1992).