Downy Mildew (Plasmopara viticola) is a well characterized plant pathogen which is known to infect a large number of grape cultivars (Vitis spp.). Downy mildew affects all parts of the plant, including leaves, shoots, buds, stems and fruit, leading to significant decreases in crop quality and on occasions complete loss of yield. This study investigates the ability of three bio-elicitors namely; Trichoderma harzianum, Streptomyces plicatus and Pseudomonas fluorescens to induce elevated levels of resistance in cv. Tifey cultivars in the face of P. viticola infection. In addition the study will explore some of the specific biochemical changes occurring within the plant in response to treatment with particular bio-elicitors with particular focus on changes in protein expression and levels of photosynthetic pigments. Enzyme activities such as peroxidise, polyphenoloxidase, chitinase and β-l, 3 glucanase were determined using spectroscopic methods, photosynthetic pigment level were determined in a similar manner. Protein expression patterns were analysed by polyacrylamide gel electrophoresis (SDS PAGE). The greatest reduction for disease severity was observed in response to treatment with T. harzianum at 1x10-6 spore mL-1 and followed by S. plicatus at 1x10-8 CFU mL-1. Both chlorophyll and carotene levels were increased in response to treatment with T. harzianum followed by P. fluorescens when compared to an infected untreated control. Significant diversity was observed in terms of enzyme activity depending on the type of elicitor employed. SDS PAGE analysis for grape seedlings showed considerable diversity in protein expression levels between biotic treatments. Pearson cluster analysis showed that protein expression patterns for treatments with S. plicatus and P. fluorescence treatment were highly similar (95.76%), T. harzianum (94.25%) clustered separately to S. plicatus and P. fluorescence indicating a possible differential response to fungal and bacterial elicitors. This study suggests that the use of bio-elicitors may provide an effective alternative to fungicides in the quest to control downy mildew disease in grapes.
Medhat A. El-Naggar, Muneera D.F. Alkahtani, Mohamed A. Yassin and Kadry M. Morsy, 2012. New Approach to Acquired Resistance Enhancement Against Plasmopara viticola Using Different Biotic Inducers. Journal of Plant Sciences, 7: 67-77.